Biological Evolution Flashcards by Rei Goh

explain why population is the smallest unit that can evolve

evolution is measured by the change in allele frequency in the gene pool of a population over successive generations
an individual has the same genetic makeup throughout its life, and it represents only one generation (does not evolve during its lifetime)
natural selection acts on individuals’ inherited traits and affects their survivial and reproductive success relative to others
individuals must be able to interbreed with other members (constituting a population) to produce offspring and pass on the allele coding for advantageous traits

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suggest why different species of picture-wing fly evolved on different islands

allopatric speciation has occurred as there was geographical isolation due to presence of water bodies separating the islands
different environment present on different islands exerts different selection pressures, allow for divergence by natural selection
further divergence by genetic drift, allele frequency in gene pools changes such that gene pools become distinct over time
flies from different islands become reproductively isolated and cannot interbreed to produce fertile, viable offspring, no gene flow between populations

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explain how homologous structures provide evidence to support the theory of evolution

homologous structures were derived from a common ancestor due to a common set of genes
although the structures have different functions, they have the same bone arrangment/similar bone structure
structures have been modified for different purposes due to different selection pressures in different environments over time, leading to divergent evolution

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explain how the evolutionary theory accounts for the similar shape of two distantly related animals

analagous structures are derived from different ancestors
as a result of similar selection pressures exerted by similar environment, leading to convergent evolution

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the dolphin has pelvic bones that do not function anymore. explain how this trait provides evidence for its phylogeny

it is a vestigial structure similar to functional pelvic bones in other mammals
indicates likelihood of a common ancestor with other mammals
from which a common set of genes responsible for the structures have been inherited

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briefly explain the molecular evidence supporting the evolutionary relationship between morphologically diverse plants and animals

similarities in DNA/RNA/amino acid sequences eg. haemoglobin
same basic genetic machinery e.g. DNA replication, transcription, translation
universal genetic code
same organelles in all eukaryotic cells e.g. ribosomes
presence of common biomolecules (ATP as universal energy currency and nucleic acid as genetic material)
all these evidences suggest common ancestry with the inheritance of a common set of genes

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state what is meant by gene mutation

change in one or a few nucleotide sequence, substitution/deletion/insertion of a few nucleotides/bases

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explain why some gene mutation do not result in a change in amino acid

genetic code is degenerate
an amino acid can be coded for by more than one codon
mutation could take place in a non-coding region e.g. intron which is removed during RNA splicing and is not expressed

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explain what direct evidence exists for time scale

time scale is derived by radiometric dating of rock strata and also by the fossil records which shows when the various species appeared

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suggest why the apparent rate of accumulation of gene mutations in the coding sections is slower

mutations in coding sections will usually disupt protein function
this is disadvantageous/selected against and so mutation is not passed on to subsequent generations
gene mutations in non-coding regions are not phenotypically expressed, hence they do not come under selection pressure and so can accumulate more quickly

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explain the relationship between classification and phylogeny

phylogeny is a type/subset of classification
classification is the organisation of species according to particular characteristics without considering the evolutionary relationship between species
phylogeny is the organisation of species according to particular characteristics by taking into consideration of the evolutionary relationships between species

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explain why molecular evidence is better than morphological evidence in determining phylogeny

molecular evidence is unambiguous and objective while morphological evidence is subjective
molecular evidence is quantifiable while in morphological evidence traits may be qualititative and cannot be quantified
molecular evidence is open to statistical analysis while in morphological evidence statistical software cannot be used to quantify differences
in molecular evidence, silent mutations taken into consideration when quantifying differences while in morphological evidence, silent mutation may not be expressed in phenotypes
molecular evidence able to distinguish between convergent and divergent evolution while in morphological evidence, similarities may be due to convergent evolution

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suggest why different species of picture-wing fly show different chromosome banding

different DNA sequences are present in different chromosomes of different species of flies due to mutations
differences are due to presence of different genes and gene loci between different species

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describe how classification differs from phylogeny

classification is based on their shared/common characteristics
phylogeny is based on evolutionary history of species
with the use of fossil records, homologous structures and molecular data which includes protein and DNA/RNA sequuences
phylogeny involves the passing of genes from ancestors to descendants
classification may not take into account evolutionary relationships while in phylogeny, evolutionary relationships with other species can be represented graphically through phylogenetic trees
one method of classification is to place organisms into taxonomic groups, which include kingdom, phylum, class, order, family, genus and species (King Philip Came Over For Good Soup) with the use of the binomial nomenclature system for naming species/organisms
phylogeny refers to the organisation of organisms into clades

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describe the environmental factors that act as forces of natural selection on finches in the Galapagos Islands

type of food available
availability of food
competition for available food

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explain how species are formed and the part that natural selection plays in the process

by allopatric speciation due to geographical isolation of two populations of a species/sympatric speciation due to behavioural/physiological isolation of two populations of a species
different environment will exert different seelection pressure/each population is subjected to a different selection pressure
in each population, organisms with traits which enable them to be better adapted to the environment will be selected for
these organisms are more likely to survive and reproduce/have higher reproductive success and pass on their alleles coding for such advantageous traits to their offspring
allele frequences of these advantageous traits will increase in the population
the 2 populations/gene pools will evolve differently/divergently
over time, the two populations have distinct gene pools
populations become reproductively isolated such that the organisms in different populations can no longer interbreed and produce viable and fertile offspring
no gene flow between populations

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with reference to industrial melanism in peppered moths, explain how an environment factor acts as a force of natural selection

colour of peppered moth, Biston betularia is either melanic or light coloured
pollution/industrial revolution is the environmental factor
darkened tree trunks and killed off lichens
against a dark background, light-coloured moths are selected against/dark-coloured moths are selected for
as they would be seen easily and eaten by insect-eating birds/as they were camouflaged from predators
dark-coloured moths have higher reproductive success and pass the allele for melanic form to their offspring
increased frequency in allele for melanic form in gene pool over time

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explain how biogeography supports the evolutionary deductions based on homologies

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deduction from homologies suggest a common descent among different species
biogeography: the study of the geographic distribution of species
species are not evenly distributed
closely related species are found closer together than distantly related species
most island species are closely related to species from the nearest mainland/neighboring island
distribution pattern suggest that species with homologous structures evolved from common ancestors
but are limited in their ability to colonise similar habitats far away
species with homologous structures but are found far away from each other/different continents can be explained by continental drift
present day distribution of marsupials

explain how fossil record supports the evolutionary deductions based on homologies

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deduction from homologies suggests a common descent among different species
fossil records: preserved remains/traces of past organisms
the parts of the organism which are rich in minerals harden as fossils
comparison of fossils enables deciphering of anatomical homology
supporting the idea that diversity of life arose from a common descent
by comparing homologous structures between fossils, order of evolution can be determined by order of appearance of fossils
deeper layer of strata contains fossils of older organisms
shallower layer of strata contains fossils of younger organisms
discovery of transitional fossils link older organisms to modern species
fossils allow scientists to deduce evolutionary history/draw phylogenetic trees

explain how bacteria evolve in the presence of antibiotics as well as its implication on antibiotic resistance

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there is pre-existing genetic variation in a bacterial population in the form of antibiotic sensitivity and antibiotic resistance
due to mutations, allele coding for antibiotic resistance can also be acquired through transformation, transduction and/or conjugation
where bacteria can take up foreign DNA (allele coding for antibiotic resistance from external environment and integrate into genome via homologous recombination (transformation))
where bacteriophages can transfer allele coding for antibiotic resistance from one bacterium to another (transduction)
where F plasmid (containing allele coding for antibiotic resistance) can be transferred from an F+ cell to an F- cell (conjugation)
antibiotics act as selection pressure to select against non-resistant bacteria/antibiotics select for bacteria which are resistant to antibiotics
bacteria that are antibiotic resistance are more likely to survive, divide by binary fission and pass down the allele coding for antibiotic resistance to subsequent generations of bacterial cells
over time, frequency of allele coding for antibiotic resistance increases in the gene pool
allele frequency may also change due to genetic drift
current antibiotics may be rendered ineffective
other types/different combinations of antibiotics need to be used

describe the differences between homologous and analogous structures

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analogous structures are derived from different ancestors but homologous structures are derived from a common ancestor/shared ancestry
analogous structures evolved due to similar selection pressures resulting in similar adaptations/convergent evolution, but homologous structures evolved due to exposure to different selection pressures/divergent evolution
analogous structures may be similar in function but not in structure, but homologous structures may be similar in structure but not in function

suggest how genetic variation may be preserved in a natural population

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diploid nature of organisms allows for recessive alleles to be preserved through heterozygous individuals
when heterozygotes have a selective advantage over homozygotes, the two alleles will be maintained at that locus by natural selection
neutral mutations do not affect phenotype of the organism/confer selective advantage/disadvantage to the organism, thus are not acted on by natural selection

describe the prevalence of sickle cell anaemia in malaria-stricken areas of Africa

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base substitution resulting beta globin chain has a hydrophobic valine instead of hydrophilic glutamic acid
folding of protein affected, leading to specific 3D conformation of haemoglobin to change, forming HbS
at low oxygen concentration, HbS molecules would clump together due to hydrophobic areas on different molecules sticking together, polymerising to form fibres
homozygotes die of anaemia or malaria and are selected against
HbS allele protects individuals from malaria and so the heterozygote with sickle cell trait is selected for
this is because when the malarial parasite enters the bloodstream, RBCs with HbS become sickle cell-shaped and die, trapping the parasite in them and hence reducing infection
heterozygotes have higher reproductive success than both homozygotes, passing down the HbS allele to offspring
over time, frequency of HbS allele increases in the gene pool of the population

describe the role of meiosis in natural selection

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meiosis produces genetically varied gametes
leading to formation of genetically varied organisms due to random fusion of gametes
in prophase I, crossing over between non-sister chromatids of homologous chromosomes occurs, results in new combination of alleles
during metaphase I, independent assortment of homologous chromosomes occurs resulting in maternal and paternal chromosomes to be randomly distributed to opposite poles of the cells
during anaphase I, segregation of homologous chromosomes to opposite poles occurs, resulting in the formation of haploid gametes
for natural selection to occur, genetic variation must be present in the population
in the presence of environmental change, the environment wil select for the organisms with the selective advantage
these organisms have a higher reproductive success and pass on their alleles coding for advantageous traits to their offspring
lack of genetic variation may lead to death of all members in the population due to the type of selection pressure present
variation allows continuation of the species in the presence of changes in the environment/increase frequency of alleles in the population
promoting speciation/evolution will not occur

explain how mutations for antibiotic resistance spread so rapidly among bacteria

* largely because bacteria reproduce very quickly * mutation can be quickly passed on to large numbers of descendents via plasmids during binary fission * thorugh conjugation, whereby transfer of antibiotic resistant genes occurs across a conjugation tube * thorugh transformation, whereby antibiotic resistance genes are taken up by competent bacterial cells through transient pores in the bacterial cell wall

outline the role of isolating mechanisms in the evolution of new species

* the biological species concept defines a species as a population, whose members are actually or potentially capable of interbreeding with one another, in a natural environment, to produce viable and fertile offspring * allopatric speciation occurs through geographical isolation of two populations or groups of populations * populations are separated by a physical barrier (mountains, oceans/rivers) * sympatric speciation occurs through behavioural/physiological isolation within the same geographical isolation * in behavioural isolation, mating rituals are different and so mating does not take place * for physiological isolation, interbreeding between individuals is prevented by temporal isolation where species reproduce in different seasons or at different times of the day/mechanical isolation where reproductive structures do not allow for mating/gamete incompatibility where gametes do not meet or fuse with each other/hybrid inviability or infertility * gene flow is prevented among populations * gene pools of each population react differently to the processes of natural selection and genetic drift, populations evolve divergently * each population has distinct gene pools * over time, individuals of each population cannot interbreed naturally to produce viable, fertile offspring and are reproductively isolated, forming different species

explain how substitution of one nucleotide in coding DNA can be selected for to bring about evolution

* results in new codon formed * giving rise to a new amino acid sequence * new amino acid has R group with different chemical properties compared to the original amino acid * 3D conformation of protein is changed * resulting in a protein with altered function * which in turn results in a different phenotype which is an advantageous trait * individuals with this mutant allele coding for the advantageous trait are selected for * they have higher reproductive success, passing on the mutant allele coding for the advantageous trait to their offspring * over time, frequency of mutant allele increases in the gene pool of the population

outline what is meant by stabilising selection

a form of natural selection which occurs in a population of organisms where the environment selects for the organisms with phenotypes that are around the mean and selects against extreme phenotypes

state one condition under which stabilising selection takes place

takes place in a non-changing environment

explain the significance of the branching points in the phylogenetic tree

* a branching point represents a speciation event where a single ancestral lineage gives rise to the two daughter lineages/species * tips of the branches represents descendants of that ancestor * organisms that share the same branching points are those that diverged more recently

suggest reasons why mitochondrial DNA is useful in examining the evolutionary relationships between different species

* mitochondria are present in large numbers in each cell hence fewer samples required * mitochondria are common in all species, valid basis for comparison between distantly related species * there are poorly conserved regions of mitchondrial DNA, used to resolve differences between closely related species * there are highly conserved sequences of mitochondrial DNA, used to detect homology even in distantly related species

explain how the fossil record can be used to support evolution

* fossil record is based on the sequence in which fossils have accumulated in rock strata/allows chronological order of fossils to be revealed * young strata found on top of older ones * radiometric/carbon dating is used to date rocks * discovery of transitional/intermediate fossils link older organisms to modern species shows new species appearing and others disappearing * support the idea that diversity of life arose from evolution * used to construct phylogenetic trees

explain the term biogeography and how the resemblance between two types of mammals could have arisen mdespite being found in different geographical regions

* refers to the study of the geographical distribution of species * analogous structures arose due to convergent evolution * similar environments provided similar selective pressures (similar predators) * causing 2 species of mammals from different ancestors to adapt to their environment in similar ways

explain the meaning of "selection pressure"

an effect that gives a fitness advantage to specific phenotypes in a population

explain how environmental factors can act as stabilising forces of natural selection in an isolated pool after the initial evolution of a new species

* environmental conditions remain the same within each pool * fishes with particular set of traits that are well adapted to conditions in each pool are selected for * extreme phenotypes are selected against

suggest what may happen if water levels rose and the isolated pools once more formed an extensive lake system

* depending on extent of reproductive isolation that has occurred, there may or may not be interbreeding * competition between species may occur, leading to reduction in number of species

suggest why there is more divergence in some regions of DNA than in others

* some regions of DNA are more prone to mutation than others * mutation happening in some regions are likely to be fatal so they are not sen in populations as they may have been selected against * there tend to be less divergence if base sequence is part of an important gene (exon) * this causes change to essential parts of protein, changing the 3D conformation of the protein and hence changing the protein's function

state the reason for the bent grass populations showing a continuous range of copper tolerance rather than two distinct groups of tolerant and non-tolerant plants

copper tolerance is due to a few genes/polygenic/affected by the environment/presence of copper in environment causes increased expression of genes

briefly describe how phylogenetic species concept could be used to determine if the two types of grasses are different species or not

anatomical and molecular characteristics compared to determine genetic history/species defined as a set of organisms with a unique genetic history

briefly describe how morphological species concept could be used to determine if the two types of grasses are different species or not

based on the physical structure/structural features of the two types of grasses

briefly describe how biological species concept could be used to determine if the two types of grasses are different species or not

if the two species are unable to produce viable fertile offspring upon cross fertilisation, they will be considered different species/species is a population/group of organisms whose members have the potential to interbreed and produce viable fertile offspring

suggest why a speciation event is unlikely to occur in a population of beetles as a result of climate change (assuming little difference in beetle size and they are in the same environment)

* no reproductive islation between two beetle phenotypes/there is gene flow within population/different beetle sizes can interbreed to produce fertile and viable offspring * little differences in beetle size in population, resulting in a more homogenous population and less genetic differences * not enough genetic diversity to prevent gene flow/no significant accumulation of different mutations

describe the limitations of using morphology in classifying species

* individuals in the same species may look very different depending on their gender/stage of life cycle * individuals which are not related may have similar structures due to convergent evolution (similar selection pressures) * differences between species at genetic level (silent or neutral mutations) may not show up in the phenotype * subjective where different taxonomists may interpret morphological traits differently * traits may be qualitative and cannot be quantified * statistical software cannot be used to analyse differences

Biological Evolution Flashcards

(44 cards)