biological evolution Flashcards

Question

what is the definition of population?

Answer 1

1. a group of individuals of the same species that live in a defined geographic area 2. individuals within a population are capable of interbreeding and producing fertile offspring 3. individuals within a population are considered as belonging to a sexually reproducing species, in which the individuals share a common gene pool. random mating occurs in the population and therefore genes of individuals are free to mix within the gene pool

Answer 2

1. the total collection of all genes of all breeding individuals in a population at any one time 2. the gene pool is dynamic, and each population has a gene pool

Answer 3

the relative proportion of the alleles of a gene present in a population

Answer 4

the relative proportion of a particular genotype present in a population

Answer 5

1. it states that the frequencies of alleles and genotypes in a population’s gene pool remain constant from generation to generation, provided that only mendelian segregation and recombination of alleles are at work 2. the model describes a gene pool whose various alleles frequencies are at equilibrium under certain conditions. for instance, the proportion of dominant and recessive alleles of a particular gene in a population always remains the same 3. the model predicts genetic equilibrium, and thus is only attainable in non-evolving populations

Answer 6

1. the population is large - changes in the gene frequencies of large populations are less likely to occur by chance. 2. random mating occurs - indicates that there is no tendency for certain genotypes to mate with other specific genotypes 3. no gene flow - the net movement of individuals between populations must not be extensive enough to change gene frequencies 4. no mutations occur - by introducing or removing gene from chromosomes or by changing one allele into antoher, mutations modify the gene pool 5. no natural selection occurs - all genotypes must be equally adaptive and reproduce equally well

Answer 7

1. in 1977, the G. fortis population on the island of daphne major was decimated by a long period of drought. of some 1200 birds, only 180 survived 2. during the drought, small, soft seeds were in short supply and the finches mostly fed on large, hard seeds that were more plentiful. as such, birds with larger and deeper beaks were better able to crack and eat these larger seeds, and they survived at a higher rate 3. the average beak depth in the next generation of G. fortis was greater than it had been in the pre-drought population, showing that the finch population had evolved by natural selection

Answer 8

1. natural selection 2. genetic drift 3. gene flow

Answer 9

1. random mutations within pre-existing genes are a source of new alleles that are new heritable variations on which other evolutionary processes can act. 2. the mutation from one allele to another can change the allele frequency in the gene pool of a population 3. mutations are rare and slow though, so they have little effect on the hardy-weinberg equilibrium

Answer 10

1. key potential source of variation are the duplication of genes due to errors in meiosis and slippage during DNA replication. duplications of large chromosome segments are often harmful, but the duplication of smaller pieces of DNA may not be 2. gene duplications can result in an expanded genome with new genes that may take on new functions 3. for example, the remote ancestors of mammals had a single gene for detecting odours that has since been duplicted many times, allowing for humans to develop 350 functional olfactory receptor genes.

Answer 11

1. the process by which certain individuals that are better adapted to an environment survive to reproduce 2. there is reproductive success of fitter individuals over those that are less fit, increasing the frequency of favourable genotypes in the gene pool, and the resultant population becomes adapted to its particular environment

Answer 12

1. directional selection favours one extreme of the phenotype range, and shifts the population mean for the selected character 2. it acts to eliminate the other extreme phenotype and the alleles promoting this extreme become less frequent in the popuation 3. this type of selection usually follows a changing environment

Answer 13

1. before industrialisation, almost 100% of moths were pale, and the black mutants were subjected to greater predation from birds as they were conspicuous against the light-coloured lichen covered trees 2. during industrialisation, the smoke, combustion and soot had destroyed the lichen and blackened the bark of tree trunks. the black peppered moths were well-camoflaged but the white peppered moths were visible and were predated upon by birds, leading to a higher frequency of black peppered moths 3. since pollution abatement, the light forms have been making a comeback, due to less soot present on the bark of trees

Answer 14

1. genetic variaties of this species, known as methicillin resistant S. aureus, are formidable pathogens. they are resistant to methicillin, able to colonise host cells, have increased gene exchange and present in virulent forms of MRSA such as clone USA300, a strain that can cause “flesh-eating disease” 2. in 1945, more than 20% of the S. aureus strains seen in hospitals were already resistant to penicillin, as they had penicillinase. therefore, methicillin was used instead, by deactivating a protein that bacteria use to synthesise their cell walls. however, S. aureus populations exhibited variations in how strongly their members were affected by the drug, as some were able to synthesise their cell walls using a different protein that was not affected by methicillin, reproducing at higher rates 2. these resistant individuals become increasingly common, leading to the spread of MRSA, where some strains are resistant to multiple antibiotics, because bacteria can exchange genes with members of their own and other species.

Answer 15

1. stabilising selection favours the existing mean and both extremes are selected against, leading to a reduction in variance and favouring intermediate phenotypes 2. this is typical of an unchanging environment where competition is not severe

Answer 16

1. infants with intermediate birth weight of between 7-8 pounds have the highest survival rate and are at a selective advantage. 2. both smaller and larger babies have a greater tendency to die than those around the most frequent weight

Answer 17

1. selection against one of the homozygotes. when one homozygous genotype has a lower fitness than the other two genotypes, the frequency of the deleterious allele will tend to decrease until it is completely eliminated 2. when both homozygous conditions have lower fitness than the heterozygote, this leads to heterozygote advantage and may result in the stable coexistence of both alleles in the population. heterozygote advantage favours individuals with copies of both alleles, and thus works to maintain both alleles in the population

Answer 18

1. the mutant allele, known has Hbs, produces a form of haemoglobin that differs from the normal form by just one amino acid from the beta-chain, but causes red blood cells containing mutated haemoglobin to alter their shape to become sickle cells which have a tendency to clump together and work less efficiently 2. however, the Hbs allele offers considerable protection against malaria, as sickle cells have low potassium levels, which causes plasmodium parasites inside these cells to die. this results in a heterozygous advantage, where the Hbs allele is present in moderately high frequencies in parts of africa and asia despite its harmful effects. 3. this is called a balanced lethal system because neither of the homozygotes produces a phenotype that survives, but the heterozygous is viable.

Answer 19

disruptive selection eliminates intermediate phenotypes and favours extreme phenotypes

Answer 20

1. data has shown that individuals with either very short or very long beaks survive best and that birds with intermediate phenotypes are at a disadvantage 2. birds with small beaks crack and eat small seeds efficiently, while birds with large beaks handle large seeds efficiently. birds with intermediate beaks have trouble with both, so alleles associated with medium-sized beaks are subject to purifying selection

Answer 21

1. if small-beaked seedcrackers begin mating with other small-beaked individuals, their offspring would tend to be small-beaked and would feed on small seeds. if large-beaked individuals chose only other large-beaked individuals as mats, they would tend to produce large-beaked offspring that would feed on large seeds 2. disruptive selection makes it possible that the gene pool may become split into two distinct gene pools, resulting in two distinct populations which may eventually form two new species

Answer 22

1. competition for resources is most intense among members of the same species, as they frequent the same districts, require the same food, and are expoed to the same dangers. 2. no two competing organisms have such similar requirements for survival as do two members of the same species, and so they compete to a lesser extent than do individuals within a species

Answer 23

1. coevolution between predators and prey is a sort of biologica arms race, with each side evolving new adaptations in respose to escalations by the other 2. for example, wolf predation selects against slow or careless deer, thus leaving more-alter and faster deer to reproduce and pass on these traits. the resulting alter, swift deer select against slow, clumsy wolves because such predators cannot acquire enough food

Answer 24

1. the random change of allele and genotype frequencies, as a result of chance alone 2. can differ from generation to generation in a small gene pool

Answer 25

1. genetic drift is significant in small populations - change events can cause an allele to be disproportionate over or underrepresented in the next generation, and alter allele frequencies substantially only in small populations 2. genetic drift causes random change of allele frequencies - an allele may increase in frequency one year, and then decrease the next. unlike natural selection, which in a given environment consistently favours some alleles over others, genetic drift causes allele frequencies to change at random over time 3. genetic drift can lead to loss of genetic variation within populations and creates genetic divergence between populations - by causing allele frequencies to fluctuate randomly over time, genetic drift can eliminate alleles from a population. because evolution depends on genetic variation, such losses can influence how effectively a population can adapt to a change in the environment 4. genetic drift can cause harmful alleles to become fixed - alleles can be lost or become fixed entirely by chance through genetic drift, and are as likely to be harmful to the organism as to be beneficial or of no effect. when drift leads to the fixation of harmful alleles, the survival of a small population can be threatened.

Answer 26

founder effect occurs when one or few individuals colonise a habitat isolated from their place of origin or new to that species. the alleles they carry will be a significant fraction of the gene pool

Answer 27

1. about 200 members of the amish religion migrated from switzerland to pennsylvania between 1720 and 1770. since that time, virtually all the pennsylvania amish moved to lancaster county and have remained reproductively isolated from non-amish americans. 2. it was discovered that they had an allele frequency for ellis-van creveld syndrom of about 0.07, compared with a frequency of less than 0.001 in the general population 3. one couple who immigrated in 1744 carried the allele and inbreeding among the amish passed the allele along to their descendants. additionally, by change, ellis-van creveld carriers had more children than the amish average, further increasing the allele frequency for genetic drift

Answer 28

1. it occurs when natural disasters, diseases or predators may kill large numbers of individuals, causing drastic short-term reductions of a population size. 2. this will result in the survivors representing a small random portion of original gene pool. alleles may be under-represented, over-represented and even eliminated 3. even when the population increases to its original size, a portion of its original genetic diversity remains lost. this leads to reduction and restriction in genetic variability, which may explain the problem with many endangered species

Answer 29

1. when praries were converted to farmland and other uses during the 19 and 20 centuries, the nuber of greater prairie chickens plummeted 2. only two illinois populations remained, which together harboured fewer than 50 birds. the few surviving birds had low levels of genetic variation, and less than 50% of their eggs hatched, compared to much higher hatching rates of the larger populations elsewhere 3. this suggests that genetic drift during the bottleneck may have led to a loss of genetic variation and an increase in the frequency of harmful alleles, leading to the low hatching rate. researchers found that the greater prairie chicken population had lost 9 alleles present in the museum specimens, and had fewer alleles per locus than the pre-bottleneck illinois populations

Answer 30

1. gene flow is the movement of genes from one population to another 2. this may be achieved by the migration of fertile individuals from one population to another and breeding in that new population 3. a population can therefore gain or lose alleles by gene flow

Answer 31

1. constructive force - if its spreads a beneficial mutation that arises in one population to other populations 2. constraining force - if it impedes adaptation within a population by the continual flow of inferior alleles from other populations 3. gene flow among populations tends to reduce differenes between populations that have accumulated as a result of natural selection or genetic drift 4. gene flow can result in neighbouring populations combining into a single population with a common gene pool

Answer 32

1. gene flow has resulted in the worldwide spread of several insecticide-resistance alleles in the mosquito cluex pipiens, a vector of west nile virus and other diseases. 2. each of these alleles has a unique genetic signature that allowed researchers to document that it arose by mutation in only one or a few geographic locations 3. in their population of origin, these allelses increased becayse they provided insecticide resistance, and these alleles were then transferred to new populations where their frequencies increased as a result of natural selection

Answer 33

1. although mining activities ceased hundreds of years ago, the concentration of metal ions in the soil is still much greater than in surrounding areas. high concentrations of heavy metals are generally toxic to plants, but alleles of certain genes confer the ability to grow on soils high in heavy metals. thus, we would expect the resistance allele to occur with a frequency of 100% on mine sites and 0% elsewhere. 2. heavy-metal tolerance has been studied intensively in the slender bent grass agrostis tenuis, in which the resistance allele occurs at intermediate levels in many areas. this is because pollen grains and the alleles they carry can move great distances, leading to levels of gene flow between mine sites and unpolluted areas high enough to counteract the effects of natural selection

Answer 34

1. when the porportion of individuals that have favourable traits increase, which improves the match between a species and its environment 2. natural selection is the only evolutionary mechanism that consistently leads to adaptive evolution, as genetic drift can cause the frequency of a slightly beneficial allele to increase, but can also cause the frequency of such an allele to decrease. similarly, gene flow may introduce alleles that are advantageous or ones that are disadvantageous

Answer 35

1. diploidy 2. balanced polymorphism

Answer 36

1. a considerable amount of genetic variation is hidden from selection in the form of recessive alleles. recessive alleles that are less favourable than their dominant counterparts, or even harmful in the prevailing environment, can persist because they are propagated in hetereozygous individuals 2. the latent variation is exposed to natural selection only when both parents carry the same recessive allele and combine two copies in one zygote. this happens only if the frequency of the recessive allele is very low. the rarer the recessive allele, the greater the degree of protection 3. heterozygous protection maintains a huge pool of alleles that might not be favoured under present conditions but some of which could bring new benefits when the environment changes

Answer 37

1. it is the condition in which many species of organisms have two or more forms that are genetically distinct from one another, but which are contained within the same interbreeding population 2. transient polymorphism occurs when one form is gradually replaced by the other.

Answer 38

1. balancing selection occurs when natural selection maintains stable frequencies or two or more phenotypic forms in a population, in a state called balanced polymorphism

Answer 39

1. it is a type of balancing selection that maintains two different phenotypic forms in a population 2. the relative fitness of different genotypes is related to how frequently they occur in the population, and the fitness of a genotype declins if it becomes too common in the population

Answer 40

1. the scale-eating fish attack other fish from behind, darting in to remove a few scales from the flank of their prey. some are left-jawed nad some are right-jawed, with the right-jawed allele being dominant to the left-jawed allele 2. prey species guard against attack from whatever phenotype of scale-eating fish is most common in the lake. thus, year to year, selection favours whichever mouth phenotype is least common. as a result, the frequency of the left and right jawed fish oscillates over sime and balancing selection keeps the frequency of each phenotype close to 50%

Answer 41

1. a genetically distinct group of natural population of organisms that share a common gene pool 2. a group of genetically compatible interbreeding natural populations that is genetically isolated from other such groups 3. the purpose is to identify species, to understand the extent to which the integrity of the gene pools is proteected and the nature of hybridisation

Answer 42

1. a species is a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are unable to product viable, fertile offspring with members of other populations 2. the members of a biological species are united by being reproductively compatible

Answer 43

1. the existence of biological factors that impede members of two species from producing viable, fertile hybrids 2. these factors are known as reproductive isolating mechanisms (RIMs) and restrict individuals of one species from interbreeding, or exhanging genes

Answer 44

1. barriers that impede mating between species or hinder the fertilisation of ove if members of different species attempt to mate, preventing the formation of zygotes by blocking fertilisation

Answer 45

1. habitat isolation - different species may occupy different habitats so they never come in contact with each other 2. temporal isolation - species have different mating of flowering seasons or times of day, or become sexually mature at different times of the year 3. behavioural isolation - sexual attraction between males and females of different animal species is limited due to differences in behaviour or physiology 4. physiological isolation - morphological features such as size and incompatible genitalia may prevent two members of different species from interbreeding. gametes may also fail to unite with each other, as the male and female gametes fail to attract and are unable to fuse

Answer 46

1. barriers that prevent the hybrid zygote from developing into a viable, fertile adult, and only occur when prezygotic ones are overcome

Answer 47

1. physiological isolation - the egg of one species is fertilised by the sperm from another species but the fertilised egg fails to develop past the early embryonic stages. alternatively, the interspecies hybrid survives, but it is sterile and succeeding generations become increasingly inviable, due to the formation of less fit genotypes

Answer 48

1. its focus on reproductive barriers, which directs our attention to how speciation occurs, by the evolution of reproductive isolation 2. speciation is the process by which one species splits into two or more species, and such analysis can distinguish groups of individuals that are sufficiently different to be considered separate species

Answer 49

1. there is no way to evaluate the reproductive isolation of fossils 2. the biological species concept does not apply to organisms that reproduce asexually. prokaryotes transfer genes by conjugation, transformation and transduction but these transfers are different from sexual recombination, some plants and animals are hermaphrodites and carry out self-fertilisation 3. there are many pairs of species that are morphologically and ecologically distinct, but yet gene flow occurs between them, forming rare hybrids between different species which are viable, sterile offspring. 4. some individuals of the same species rarely interbreed

Answer 50

1. a species is the smallest group of individuals that share a common ancestor, and have a shared and unique evolutionary history 2. phylogenetic histories can be traced by comparing its morphological characteristics with those of other organisms. these sorts of analyses can distinguish groups that are generally similar yet different enough to be considered separate species.

Answer 51

1. advantages - such analysis can distinguish groups of individuals that are sufficiently different to be considered separate species. phylogenetic information reveals the existence of ‘sibling species’ that appear so similar they cannot be distinguished on morphological grounds 2. limitations - the difficulty is in determining the degree of difference required to indicate separate species

Answer 52

1. it characterises a species by body shape and other structural features 2. organisms are classified as the same species if their anatomical traits appear to be very similar 3. we are forced to distinguish between many species in this way because there is little to no infomation about their mating capabilities

Answer 53

1. advantages - it can be applied to all organisms whether they are reproducing asexually or sexually. it can be useful even without information on the extent of gene flow 2. limitations - it may be difficult to decide how many morphological characters to consider when characterising individuals. it is difficult to analyse qualitative traits that vaery in a continuous way among members of the same species. researchers often disagree about how much morphological difference is necessary to separate different species 3. members of the same species sometimes look very different and conversely, members of different species sometimes look remarkably similar to each other

Answer 54

1. it views a species in terms of its ecological niche that is within its native environment, focusing on unique adaptations to particular roles in a biological community 2. species from different evolutionary branches may come to resemble one another if they have the same ecological niche, result of convergent evolution 2. species which are distributed over a wide geographical range or have occupied well-separated geographical habitats for a long period of time may show considerable phenotypic differences, result of divergent evolution

Answer 55

1. advantages - the ecological species concept accommodate asexually reproducing and sexually reproducing species. this allows for bacterial species to be distinguished, as bacterial cells of the same species are likely to use the same types of resources and grow under the same types of conditions 2. limitations - it does not take into account the species’ morphology and reproductive compatibility

Answer 56

1. it is the evolution of species, which occurs when the inherited characteristics of a population or of a species change over a period of time

Answer 57

1. the ancestral species is established to be a single species 2. all members of the species actually interbreed and are reproductively and genetically isolated from each other

Answer 58

1. subgroups of the ancestral species become divided from one another by a barrier. the populations are therefore isolated ecologically and geographically 2. members can still interbreed if brought together, and there is no particular advantage or disadvantage for interbreeding between the separated populations

Answer 59

1. an external barrier divides the populations, and gene flow between the geographically isolated populations is interrupted. variation arising within one population is not shared with the other via iterbreeding. thus, the biological species concept uses the presence of absence of gene flow among populations to delineate species boundaries 2. each population experiences a slightly different environment that delivers different selective pressures. different characters will be successful in each location. the accumulation of character driven by local environmental conditions leads to the genetic distinctiveness of each separate population. due to natural selection and changes in the gene pool, each population becomes more adapted to its own environment 3. traits that serve well in the ancestral group may now find disfavour in each newly divided population that is adapting to a different environment. each population undergoes independent evolution, and if the barrier persists, the separate populations become genetically distinct

Answer 60

1. the barrier now disappears and the different populations come into contact 2. if the reproductive isolating mechanisms are sufficiently weak as to allow free interbreeding aross the reunited populations, and such matings produce offspring that are not at some fitness disadvantage compared to offspring derived from matings between individuals from within either population, then the process of speciation halts 3. if the RIMs that developed during allopatric speciation put offspring from matings between two populations’ indivduals at a selective disadvantage, the process of speciation continues. they would diverge so substantially they they are reproductively isolated and unable to produce fertile viable offspring 4. there must be accumulation of sufficient RIMs, adaptations and genetic diversity for a new species to be formed.

Answer 61

1. the formation of new species when one population becomes geographically separated from the rest of the species and subsequently evolves by natural selection/genetic drift 2. both natural selection and genetic drift result in changes in allele frequencies in a population, but only in natural selection is the change in allele frequency adaptive 3. it is more likely to occur if the original isolated population is small, as genetic drift is more consequential in small populations. the different selection pressures of the new environment to which the population is exposed further accentuate the divergence caused by genetic drift

Answer 62

1. harris’ antelope squirrel inhabits the grand canyon’s south rim. just a few miles away on the north rim lives the closely related white-tailed antelope squirrel. 2. during its many years of geographic isolation, the small population of white-tailed antelope squirrels has diverged from the widely distributed harris’ antelope squirrels in several ways. the most evident changes are fur colour. the white-tailed antelope squirrel now has a white tail and a gray belly, in contrast to the gray tail and white belly of the harris’ antelope squirrel 3. biologists think these striking changes arose in white-tailed antelope squirrels as a result of genetic drift. because the white-tailed antelope and harris’ antelope squirrles are reproductively isolated from each other, some scientists have classified the white-tailed antelope squirrle as a different species

Answer 63

1. large interconnected lakes were formed during wetter climates of the last ice age. these lakes were populated by one or several species of pupfishes 2. over time, the climate became drier, and the large lakes dried up, leaving isolated pools 3. each pool contained a small population of pupfish that gradually diverged from the common ancestral species by genetic drift and natural selection in response to habitat differences - the high temperatures, high salt concentrations and low oxygen levels characteristic of desert springs 4. today, there are 20 or so distinct species, supspecies and populations in the area of death valley, california and ash meadows, nevada. many of the pupfishes are restricted to one or two isolated springs

Answer 64

1. darwin’s finches are birds that are derived from a small flock of grassquits that invaded the archipelago from central or south america some 2.3 million years ago. the descendants of this flock today comprise 13 species that live in the galapagos, plus a 14th species that lives on cocos island 2. consistent with their close kinship, all species of darwin’s finches are similar in body size and colouration. they range from 4 inches to 6 inches in length and from brown to black in colour. they show remarkable variation in the size and shape of their beaks. 3. the beak is the primary tool used by birds in feeding, and the enormous range of beak morphologies among the galapagos finches reflects the diversity of food they eat. 4. hence, darwin observed that there were different species of finches on the different islands of the galapagos islands. each species has a beak that is adapted to the particular food source on each respective island 5. due to the mechanisms of natural selection and changes in the gene pool, each population of finches became more adapted to its own environment on one of the different islands. due to various food sources available on the different islands, different bills had different selective advantage, and were selected differentially on different islands, allowing them a better chance of survivel within a diverse niche

Answer 65

1. the process in which a new species evolves within the same geographic region as the parental species OR geographically overlapping populations 2. the divergence of two populations in the same geographic range occurs when reproductive isolating mechanisms evolve at the start of the speciation process 3. sympatric speciation is especially common in plants, and occurs in either polyploidy or ecological isolation

Answer 66

1. polyploidy describes instances in which organisms possess more than two of the haploid chromosome set 2. polyploidy is a major factor in plant evolution, as reproductive isolation occurs in a single generation when a polyploid species with more than two sets of chromosomes arises from diploid parents

Answer 67

1. an organism that contains at least one set of chromosomes from two or more different species 2. an allodiploid describes an organism that has only 1 set of chromsomes from two different species

Answer 68

1. occurs when an organism contains two or more complete sets of chromosomes from two or more different species 2. an allotetraploid is a type of allopolyploid that contains two complete sets of chromosomes from two species, leading to a total of 4 complete sets of chromosomes

Answer 69

1. an organism which contains more than two sets of chromosomes, all derived from a single species

Answer 70

1. a failure of cell division after chromosome duplication could double a cell’s chromosomes through non-disjunction. this causes the formation of tetraploid cells 2. if one of these 4n cells gives rise to a tetraploid plant, flowers produced would have diploid gametes through meiosis 3. if self-fertilisation occurs, the resulting tetraploid zygotes would develop into plants that can produce fertile tetraploid offspring by self-pollination or by mating with other tetraploids 4. a tetraploid cannot produce fertile offspring by making with a parent plant, as this would produce triploid offspring whcih are sterile, and an odd number of chromosomes cannot form homologous pairs and separate normally during meiosis 5. the formation of a tetraploid plant is an instantaneous speciation event, as a new species, reproductively isolated from its parent species is produced in one generation

Answer 71

1. this is accomplished by applying cold or heat shock to meiotic cells or by applying colchicine to somatic cells undergoing mitosis. colchicine interferes with spidle formation and thus replicated chromosomes cannot separate at anaphase and do not migrate to the poles, leading to non-disjunction 2. when colchicine is removed, the cell can reenter interphase

Answer 72

1. economically important triploid plants such as seedless watermelons, commerical bananas etc. are propagated asexually 2. diploid bananas contain hard seeds, but the commerical triploid seedless variety has edible seeds 3. tetraploid alfalfa, coffee, peanuts and mcintosh apples are either larger or grow more vigorously than their diploid or triploid counterparts

Answer 73

1. when haploid gametes from two different species combine, the resulting hybrid is normally sterile because its chromosomes cannot pair during meiosis. this is hybrid sterility, a form of psychological isolation that occurs as a post-zygotic barrier. 2. however, the hybrid may reproduce asexually, as many plants can do 3. subsequent errors in cell division may produce chromosome duplications that result in a diploid set of chromosomes. chromosomes can now pair in meiosis, and haploid gametes will be produced. thus a fertile polyploid species has formed, and the new species has a chromosome number equal to the sum of the diploid chromosome numbers of its parent species

Answer 74

1. the new species may not compete successfully against species that are already established, so it becoms extinct 2. the allopolyploid individuals may assume a new role in the environment and so coexist with both parental species 3. the new species may successfully compete with either or both its parental species. if it has a combination of traits that confers greater fitness than either or both parental species for all or part of the original range of the parents, the hybrid species may replace the parent

Answer 75

1. the process begins with hybridisation between two wheats: the cultivated species T. monococcum (AA), and a wild species that grew as weeds at the edges of fields (BB). chromosome sets A and B of the two species would not have been able to pair at meiosis, making the AB hybrid sterile 2. an error in cell division and self-fertilisation would have produced a new species (AABB) with 28 chromosomes. this species is emmer wheat, and is used mainly for making macaroni 3. the final steps in the evolution of bread wheat occured in early farming villages, where the cultivated emmer wheat hybridised spontaneously with the closely related wild species T. tauschii (DD) which has 14 chromosomes. 4. the hybrid (ABD) was sterile, but a cell division error in this hybrid and self-fertilisation doubled the chromosome number to 42. the result was bread wheat (AABBDD)

Answer 76

1. in a history of a species, long periods of stasis appeared to be punctuated, or interrupted by short periods of rapid speciation that were triggered by changes in the environment and periods of great evolutionary stress. thus, speciation proceeded in spurts, and short periods of active evolution 2. punctuated equilibrium accounts for the abrupt appearance of a new species in the fossil record, with little or no evidence of intermediate forms. 3. few transition forms appear because few transitional forms occured during speciation

Answer 77

1. occasionally, a complete fossil record of transitional forms has been discovered and cited as a strong case of gradualism 2. the gradualism model maintains that populations slowly diverge from one another by the gradual accumulation of adaptive characteristics within each population 3. these adaptive characteristics accumulate as a result of different selective pressures encountered in different environments

Answer 78

1. domain 2. kingdom 3. phylum 4. class 5. order 6. family 7. genus 8. species

Answer 79

1. it creates order out of chaos and helps in the study and referencing of organisms 2. it reveals natural evolutionary relationships and is a guide to the study of evolutionary pathways 3. it helps with the identification of newly discovered organisms 4. it forms a basis for an international system of nomenclature

Answer 80

1. it is the large scale phenotypic changes in populations that generally warrant their placement in taxonomic groups at the species level of higher 2. studies of macroevolution seek to discover and explain major changes in species diversity through time such as occur during adaptive radiation, when many species appear, and mass extinction when many species disappear.

Answer 81

1. it is evolutionary diversification of many related species from one of a few ancestral species in a relatively short period of time

Answer 82

1. new resources and ecological opportunities 2. new ways to exploit resources (evolutionary novelties)

Answer 83

1. ecological opportunities mean the availability of new or novel types of resources that have driven a wide array of adaptive radiations 2. adaptive zones are ecological opportunities that were not exploited by an ancestral organism. when an adaptive zone is empty, a colonising species will encounter no competitors, rapidly diversifying so that it leads to efficient use of the available resources. the species develops adaptations that makes them thrive. succeeding generations diversify into new species, leading to rapid speciation from an ancestral species

Answer 84

1. the anolis’ lizard’s size and shape are correlated with the habitat it occupies. species that live on tree twigs have short legs and tails that allow them to move efficiently on narrow surfaces. species that spend most of their time clinging to broad tree trunks or running along the ground have long legs and tails, making them fast and agile on broad surfaces 2. most islands in the caribbean have a distinct suite of lizard species. each island has a species that lives only in the twigs, the ground or other distinctive habitats. an original colonising group encountered no competitors, and diversified in a way that led to efficient use of the available resources by a group of descendant species. the lizards on each island were monophyletic

Answer 85

1. evolutionary novelties originate through modifications of pre-existing structures. a change in the basic pattern of an organism produces something unique 2. usually, these evolutionary novelties are variations of some pre-existing structures called preadaptation that originally fulfilled one role but subsequetly changed in a way that was adaptive for a different role

Answer 86

1. the evolution of wings, three pairs of legs, complex mouthparts and a strong external skeleton helped insects move and feed efficiently. today, insects are the most diverse lineage on earth, with over 3 million species 2. flowers are a unique reproductive structure that helped trigger and diversification of angiosperms. because flowers are particularly efficient at attraction pollinators, the evolution of the flower made angiosperms more efficient in reproduction. today angiosperms are the most species-rich lineage of land plants 3. cichlids are a lineage of fish that evolved a unique set of jaws in their throat. these second jaws make fod processing extremely efficient. different species have throat jaws specialised for crushing snail shells, and shredding tissue. over 300 species of cichlid live in africa’s lake victoria alone 4. feathers and wings gave some dinosaurs the ability to fly. today, the lineage called birds contains about 10000 species, with representations that live in virtually every habitat of the planet

Answer 87

1. when the hawaiian honeycreepers reached hawaii, few other birds were present 2. the succeeding generations of honeycreepers quickly diversified into many new species and in the process, occupied the many available adaptive zones that on the mainland are occupies by finches, honeyeaters, tree creepers and more 3. the diversity of their bills is a good illustration of adaptive radiation, as some bills are curved to extract nectar out of tubular flowers, whereas others are short and thick for ripping away bark in search for insects

Answer 88

1. the end of a linage and occurs when the last individual of a species dies. the lost is permanent 2. extinctions have occured continually since the origin of life; by one estimate, only 1 species is alive today for every 2000 that have become extinct 3. extinction is the eventual fate for all species

Answer 89

1. extinction facilitates evolution over a period of thousands to millons of years 2. when species become extinct, their adaptive zones become vacant. 3. surviving species are presented with new evolutionary opportunities and may diverge, filling in some of the unoccupied zones. the extinct species may eventually be replaced by new species

Answer 90

1. it is the continuous, low-level extinction of species 2. members of taxonomic groups are lost gradually over long time periods without abrupt loss of large numbers

Answer 91

1. the most recent mass extinction which occured about 1 mya ago killed off many marine organisms, terrestial plants and vertebrates, including the last of dinosaurs. 2. each period of mass extinction has been followed by a period of adaptive radiation of some of the surviving groups 3. major changes in the climate could have adversely affected those plants and animals that lacked the genetic flexibility to adapt 4. changes in the environment due to catastrophes may also have caused past mass extinctions. the dust ejected from an extraterrestrial object could have block much of the sunlight, disrupting the food chain by killing many plants and terrestrial animals 5. biological factors, such as competition among species may lead to the extinction of species that cannot compete effectively. the habitats of many animal and plant species have been altered or destroyed by humans, and habitat destruction can result in a species’ extinction

Answer 92

1. microevolution is concerned with patterns of change within a population or species, while macroevolution is concerned with the overall pattern and the origin of species and higher-level taxa such as families or classes 2. microevolution has a short-term view while macroevolution has a long-term view 3. examples of microevolution are changes in allele frequency in populations, while examples of macroevolution are diversification, the demise of dinosaurs and the origin of birds

Answer 93

1. tiktaalik is a genus of extinct lobe-finned fish from the late devonian period about 375 mya, having many features akin to those of tetrapods. 2. tiktaalik has a possibility of being a representative of the evolutionary transition from fish to amphibians. it is an example from several lines of ancient sarcopterygian fish developing adapatations to the oxygen-poor shaddow-water habitats of its time, environmental conditions which are thought to have led to the evolution of tetrapods. 3. tiktaalik and similar animals may possibly be the common ancestors of the board swath of all vertebrate terrestrial fauna: amphibians, reptiles, birds and mammals. 4. the novelties accumulated as a succession of small changes over a period of 9-14 million years, is sufficient to have allowed natural selection and other microevolutionary processes to produce novel characters

Answer 94

1. it is the variety of living organisms and their range of behavioural, ecological, physiological and other adaptations in an area such as an ecosystem

Answer 95

1. a discipline of biology, involving the scientific study of the diversity of organisms, focusing on classifying organisms and determining their evolutionary relationships 2. systematists classify organisms based on current data from morphology, developmental biology, fossil records, behavioural biology and molecular biology

Answer 96

1. a component of systematics, defined as the science of naming, describing and classifying the diversity of organisms

Answer 97

1. it is the act of systematically arranging organisms into groups based on particular shared characteristics and their similarities 2. classification may not take into consideration evolutionary relationships between species

Answer 98

1. it is the organisation of species according to particular characteristics which takes into consideration the evolutionary relationships between species

Answer 99

1. phylogeny reflects evolutionary history and represents a hypothesis about patterns of evolutionary relationships among species 2. it showcases the branching relationships of organisms as they give rise to multiple descendant species over evolutionary time 3. it traces patterns of shared ancestry between lineages and shows which organisms are more closely or distantly related to one another

Answer 100

1. observations of traits are used to infer the patterns of ancestry and descent among populations. these patterns are then represented in graphical form as a phylogenetic tree 2. by mapping additional traits onto a phylogeny already created, the sequence and timing of evolutionary events can be studied

Answer 101

1. a phylogenetic tree is a hypothesis about secondary relationships 2. a phylogenetic tree is a hypothesis about the way that evolutionary history has unfolded. 3. with new evidence, the current phylogenetic tree is tested, along with our current inferences about evolutionary events

Answer 102

1. root - the common ancestors to all species on the tree 2. branch - evolution over time 3. node - the separation of one lineage into multiple distinct lineages, or the divergence of two or more species from a common ancestor 4. tip - it represents a taxon which is present today or those that that have become extinct.

Answer 103

1. the sequence of branching does not necessarily indicate the actual age of the particular species. no assumptions should be made about when a particular species evolved or how much genetic change occured in each evolutionary lineage 2. a taxon on a phylogenetic tree does not evolve from the taxon next to it

Answer 104

1. a monophyletic taxon includes an ancestral species and all its descendents 2. monophyletic taxa are natural groupings, because they represent true evolutionary relationships and include all close relatives. 3. sister taxa share a more recent common ancestor with one another than either taxon does with any other group shown on a phylogenetic tree

Answer 105

1. a polyphyletic taxon consists of several evolutionary lines that do not share the same recent common ancestor 2. members of such a group have been classified together based on their morphology because these organisms share similar feature arising from convergent evolution

Answer 106

1. a paraphyletic taxon contains a common ancestor and some, but not all of its descendants

Answer 107

1. some homologous characteristics are shared by all species because they date back to the deep ancestral past. homologous characteristics that evolved more recently are shared only within smaller groups of organisms 2. for example in tetrapods, all tetrapods possess the same basic limb bone structure, but the ancestors of tetrapods do not. 3. homologous characteristics form a nested pattern. all life shares the deepest layer, and each successive smaller group adds their own homologies to those they share with larger groups

Answer 108

1. analogy refers to a characteristic that superficially appears homologous, but is actually independently acquired. instead, it is due to adaptation to similar environments 2. this is a form of convergent evolution where similar environmental pressures and natural selection produce similar adaptations in organisms from different evolutionary lineages. 3. thus, analogous structures do not reflect evolutionary relationships between species

Answer 109

1. bats and birds descended from a common tetrapod ancestor that lived abot 320 million years ago. this common ancestor could not fly. thus, although the underlying skeletal systems of bats and birds are homologous, their wings are not 2. closer examinations reveal that a bat’s wing is far more similar to the forelimbs of cats and other mammals than to a bird’s wing 3. thus, with respect to flight, a bat’s wing is analagous, not homologous to a bird’s wing

Answer 110

1. both are large marine animals with streamlined bodies and large dorsal fins. both chase down fish and capture them between elongated jaws filled with dagger-like teeth. 2. however, ichthyosaurs and dolphins did not share a common ancestor, as ichthysaurs are reptiles and dolphins are mammals. it is logical to argue that the similarities between ichthyosaurs and dolphns result from convergent evolution 3. streamlined bodies and elongated jaws filled with sharp teeth are adaptations that help any species chase down fish in water

Answer 111

1. shared derived characters are novel traits that evolve independently from homologous traits as a result of mutation, natural selection and genetic drift 2. shared derived characters originate in a recent common ancestor and are present in its descendants 3. species that share derived characters form a clade

Answer 112

1. synapomorphes identify evolutionary branch points. speciation starts when two populations become geneticaly isolated, meaning that gene flow is reduced or absent. when genetic isolation occurs and species begin evolving independently, some of the homologous traits in each population undergo changes due to natural selection, mutation and genetic drift. these changed traits identify the populations belonging to the two independent, descendent lineages 2. synapomorphes are nested. as you move through time and trace a tree from its root to its tips, each branching event adds one or more shared, derived traits. the hierarchy described by synapomorphies also describes the hierarchy of branching events

Answer 113

1. as a basis of comparison, an outgroup which is a species or group of species from an evolutionary lineage that is known to have diverged before the lineage that includes all the species we are studying, is needed to be selected 2. a suitable outgroup can be determined based on evidence from morphology, paleontology, embryonic development and gene sequences. 3. by comparing members of the ingroup to each other and to the outgroup, we can determine which characters were derived at the various branch points of vertebrate evolution.

Answer 114

1. macromolecules that are functionally similar in two different types of organisms are considered homologous if their primary sequence is similar. such a molecular approach can help us understand phylogenetic relationships that cannot be determined by non-molecular methods such as comparative anatomy 2. since genetic sequences change over the course of many generations, due to the accumulation of mutations, DNA sequences from closely related organisms are more similar to one another than to sequences from distantly related species 3. the number of differences in certain DNA/RNA sequences or amino acid sequences between two groups of organisms reflect how much time has passed since the groups branched

Answer 115

1. if the species are very closely related, the sequences probably differ at only one or a few sites 2. in contrast, comparable nucleic acid sequences in distantly related species usually have different bases at many sites and may have different lengths. this is because insertions and deletions accumulate over long periods of time

Answer 116

1. one of the main ways is to count up the number of base pair differences and use this tally as the molecular distance between the two species

Answer 117

1. the HA protein found in influenza A can evolve rapidly from year to year to escape immune memory, and therefore even sequences from the same strain can show sizable year-to-year variation 2. when comparing more recent strains of the influenza A virus, due to genetic reassortments among bird, swine, and human influenza viruses, the HA proteins differ at a remakable 89 or 327 amino acid positions. as a result, many humans were susceptible to this new strain

Answer 118

1. human cytochrome c contains 104 amino acids of which 37 of these have been found at equivalent positions in every cytochrome c that has been sequences. 2. it has been discovered that the number of amino acid residues that differ in homologous proteins from any two species is in proportion to the phylogenetic difference between those species. the greater the degree of homology between two molecules, the more recently they have evolved from a common ancestral molecule and the closer the evolutionary relationship between the organisms 3. human and chimpanzee sequences are identical, and macaque and spider monkey are very similar to the human sequence. this implies a common and recent evolutionary divergence

Answer 119

1. molecular data is genetic. anatomical, behavioural and physiologica traits often have a genetic basis, and nucleic acid and amino acid sequence variation has a clear genetic basis that is easy to interpret 2. molecular methods can be used with all organisms, as all living organisms possess nucleic acids and proteins 3. molecular methods can be applied to a huge amount of genetic variation. an enormous amount of data can be accessed by molecular methods due to the large genome in organisms 4. the molecular approach helps us to understand phylogenetic relationships that cannot be determined by non-molecular methods such as comparative anatomy, as they offer a valid basis for comparison 5. molecular data is quantifiable, as nucleic acid and amino acid sequence data is precise, accurate and easy to quantify 6. molecular data provides information about the process of evolution 7. the database of molecular information is large and growing 8. molecular methods allow us to reconstruct phylogenies among groups of present-day prokaryotes and other microorganisms for which we have no fossil record 9. different genes evolve at different rates, even in the same evolutionary linage. molecular trees can represent short or long periods of time, depending on what genes are used.

biological evolution Flashcards

(145 cards)