chapter 18: diversity and evolution

Question 1

what is the definition of micro-evolution

Answer 1

microevolution: changes in the allele frequencies in the gene pool of a population from one generation to the next
- ( a tweak or adjustment in traits over a few generations)

Question 2

population: it is a group of ___ individuals belonging to a particular ___ and sharing the same ___

Answer 2

population: it is a group of interbreeding individuals belonging to a particular species and sharing the same ecological niche

Question 3

ecological niche: is a term used to describe the sum of a species’ use of ___ and ___ factors
- it is the interaction of the species with its ecosystems

Answer 3

ecological niche: is a term used to describe the sum of a species’ use of biotic and abiotic factors
- it is the interaction of the species with its ecosystems

biotic factors: living parts of the environment
- what it eats, what eats it, diseases it is affected by

abiotic factors: non-living parts of the environment
- temperature
- humidity
- soil type
- water availibility

Question 4

what is the DARWINIAN THEORY of evolution?

Answer 4

1. descent with modification:
- the decendent species inherited characteristics from the anscestor species but are modified over generations to better adapt to the environment
- this means that each generation in a population, on average, slightly different from the parent generation
- these differences accumulate over time to give rise to more complex differences
- can result in new species forming

2. natural selection:
- a naturally occuring process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits
- this is the primary mechanism which determines how descendants are different from their ancestors.

Question 5

what are the five principles of natural selection?

Answer 5

observation 1: overproduction of offspring
observation 2: population sizes tend to remain stable in size
observation 3: environmental resources are limited
observation 4: variation exists within a population
observation 5: much of this variation is heritable

Question 6

principles of natural selection:
observation 1: overproduction of offspring
what does this mean?

Answer 6

• all species have such high reproductive capacity, such that their population sizes would increase exponentially if all individuals that are born reproduce successfully

Question 7

principles of natural selection:
observation 2:** population sizes tend to remain stable in size**
what does this mean?

Answer 7

• although organisms are capable of producing large number of offspring, most populations remain relatively constant in numbers
• this is because most of the offspring die before they reach reproductive age

Question 8

principles of natural selection:
observation 3: environmental resources are limited

deduction: struggle for survival
- based on the first three observations, it can be deduced that individuals of a ____are constantly ____ with one another for ____ environmental resources ( like food, water, light and space)
- hence, not all organisms will survive to reach ____ ____ to reproduce as there are more individuals than the environment can ___

inference 1: production of more individuals than an environment can support leads to a ____ ____ ____ among individuals in a ___

Answer 8

principles of natural selection:
observation 3: environmental resources are limited

deduction: struggle for survival
- based on the first three observations, it can be deduced that individuals of a species are constantly **competing ** with one another for limited environmental resources ( like food, water, light and space)
- hence, not all organisms will survive to reach sexual maturity to reproduce as there are more individuals than the environment can support

inference 1: production of more individuals than an environment can support leads to a struggle for existenceamong individuals in a population

Question 9

principles of natural selection:
observation 4: variation exists within a population
what does this mean?

Answer 9

• members of a population often vary in their inherited traits
• each individual has a unique combination of traits
• some traits improve an individual’s chance of survival and reproductive success while others do not

Question 10

principles of natural selection:
observation 5: much of this variation is heritable

deduction:** survival of the fittest by natural selection**
- survival in the struggle for existence is not random, but depends on the ____ ____ of the individuals
- within a ____, some individuals who possess ____ traits survive better in the existing environmental conditions than others
- they are better adapted to survive to reach sexual maturity to produce ____ offspring
> they are more ____ (fitness: refers to the ability to produce viable offspring)
- hence, these individuals are said to be selected ____ by the environment and are at a selective ____
- they may pass on alleles ____ these favourable traits to their offspring

• conversely, less adapted individuals die before they reach sexual maturity and are able to reproduce
  > they are at a ___ ____

Answer 10

principles of natural selection:
observation 5: much of this variation is heritable

deduction:** survival of the fittest by natural selection**
- survival in the struggle for existence is not random, but depends on the heritable traits of the individuals
- within a population, some individuals who possess favourable traits survive better in the existing environmental conditions than others
- they are better adapted to survive to reach sexual maturity to produce viable offspring
> they are more fit (fitness: refers to the ability to produce viable offspring)
- hence, these individuals are said to be selected for by the environment and are at a selective advantage
- they may pass on alleles coding these favourable traits to their offspring

• conversely, less adapted individuals die before they reach sexual maturity and are able to reproduce
  > they are at a selective disadvantage

Question 11

evolution is descent with modification
inference 3:
- the ____ ability of individuals to survive and reproduce will lead to a ____ change in a population
- with ____ characteristics accumulating over generations
- over many generations, the proportion of individuals possessing the ____ traits increases in the population whereas the proportion of individuals lacking the favourable traits ___

• eventually, accumulation ( inheritance) of many favourable traits in a population of organisms over time may result in the formation of a new ___

Answer 11

evolution is descent with modification
inference 3:
- the unequal ability of individuals to survive and reproduce will lead to a gradual change in a population
- with favourable characteristics accumulating over generations
- over many generations, the proportion of individuals possessing the favourable traits increases in the population whereas the proportion of individuals lacking the favourable traits decreases

• eventually, accumulation ( inheritance) of many favourable traits in a population of organisms over time may result in the formation of a new species

Question 12

what does Neo-Darwinism Theory explain?

Answer 12

• the traits which are passed down to offspring are controlled by genes
• the inheritance of traits is through alleles passed down to offspring through gametes

the source of variation found in a population is due to:
-** gene mutations**
- chromosomal mutations
- meiosis: crossing-over and independent assortment
- fertilisation: random mating of individuals and random fusion of gametes

Question 13

evolution is said to have taken place when….

Answer 13

evolution is said to have taken place when the allele frequency in the gene pool of the population changes ( micro- evolution)

Question 14

HOW NATURAL SELECTION BRINGS ABOUT EVOLUTION
- ____ ____ is the process in which organisms with certain inherited traits/ characteristics/ phenotypes are most likely to survive and reproduce than organisms with other traits/ characteristics/ phenotypes, in a certain environment.

• ____ variation (variation in alleles in the gene pool of a population) arises because of gene ____ , chromosomal ____ , independent assortment, and crossing-over
  during meiosis and random fusion of gametes during sexual reproduction.
• As the trait of an organism is controlled by its genotype, genetic variation results in
  ____ variation among organisms within the same population
• Challenges in the environment (e.g. climate, disease, competition from other organisms,
  predation and limitation of food and other resources) will exert selection ____ on
  the individuals of the population.
  Selection pressure: Factor that reduces reproductive success in a proportion of a population
  **Reproductive success: **The ability to reproduce to produce viable and fertile offspring.
• Different selection pressures will select for different forms of the characteristic. Organisms with traits which enable them to adapt better to the environment are at a selective ____ and they will be ____ for. They are more likely to ____ and reproduce
  to pass on the ____ coding for advantageous traits to their offspring/ next generation.
• Organisms with traits that cannot adapt well to the environment are at a selective disadvantage
  and will be selected ____ . They are less likely to survive and reproduce to pass on their alleles to their offspring
• Over time and many generations, evolution occurs where the frequencies of various alleles change in the population gene pool. Frequency of alleles coding for ____ traits will
  ____ in the population, while frequency of alleles coding for less advantageous
  traits will ____ .
• The population becomes better ____ to the environment.
• Eventually, the gene pool of the descendent population may become significantly different from the ancestral population, such that it is ____ ____ from the ancestral population, and
  this may result in ____

Answer 14

HOW NATURAL SELECTION BRINGS ABOUT EVOLUTION
- natural selection is the process in which organisms with certain inherited traits/ characteristics/ phenotypes are most likely to survive and reproduce than organisms with other traits/ characteristics/ phenotypes, in a certain environment.

• genetic variation (variation in alleles in the gene pool of a population) arises because of gene mutations , chromosomal mutations , independent assortment, and crossing-over during meiosis and random fusion of gametes during sexual reproduction.
• As the trait of an organism is controlled by its genotype, genetic variation results in
  phenotypic variation among organisms within the same population
• Challenges in the environment (e.g. climate, disease, competition from other organisms,
  predation and limitation of food and other resources) will exert selection pressure on the individuals of the population.
  Selection pressure: Factor that reduces reproductive success in a proportion of a population
  **Reproductive success: **The ability to reproduce to produce viable and fertile offspring.
• Different selection pressures will select for different forms of the characteristic.
• Organisms with traits which enable them to adapt better to the environment are at a selective advantage and they will be for for.
• They are more likely to survive and reproduce to pass on the alleles coding for advantageous traits to their offspring/ next generation.
• Organisms with traits that cannot adapt well to the environment are at a selective disadvantage
  and will be selected against
• They are less likely to survive and reproduce to pass on their alleles to their offspring
• Over time and many generations, evolution occurs where the frequencies of various alleles change in the population gene pool. Frequency of alleles coding for advantageous traits will increase in the population, while frequency of alleles coding for less advantageous
  traits will decrease .
• The population becomes better adapted to the environment.
• Eventually, the gene pool of the descendent population may become significantly different from the ancestral population, such that it is reproductively isolated from the ancestral population, and this may result in speciation

Question 15

example of environmental factors as forces of natural selection:
FINCHES OF GALAPAGOS ISLANDS

Answer 15

• The Galápagos Islands consist of multiple islands, each offering DIFFERENT food resources and environmental conditions.
• A long time ago, one ancestral species of ground-dwelling, seed-eating finch migrated from the mainland of Central or South America to the Galápagos Islands.
• VARIATIONS exist in the ancestral finch population.
• When the finches colonised different islands, the different environmental conditions (e.g. availability of food types) on each island acted as DIFFERENT SELECTION PRESSURES, causing the populations to evolve in various directions.
• Over many generations, finch populations on different islands evolved different beak shapes, each adapted to a different diet — e.g. seeds, insects, flowers, or leaves.
• The GEOGRAPHICAL ISOLATION of the islands PREVENTED GENE FLOW between populations, allowing natural selection to act independently on each island.

Eventually, these populations evolved into 14 separate species, each with distinctive beaks, songs, and feeding behaviours.

🌱 Adaptive Radiation
This process, where multiple species evolve from a common ancestor to fill different ecological niches, is called adaptive radiation.

Question 16

example of environmental factors as forces of natural selection:
Shell Banding Patterns in Land Snails (Capaea nemoralis)

Answer 16

• The land snail Cepaea nemoralis shows genetic variation in its shell banding pattern and shell colour.
  Two main observable traits:
• Banding pattern: some snails have dark bands, others have unbanded shells.
• Shell colour: may be yellow, pink, or brown.
• There is a strong correlation between shell traits and habitat type due to predation pressure:

🟨 In Uniform Grassland Habitats:
The background is yellowish (due to dry grass/hay).
- Brown banded shells are more visible to predators → at a selective disadvantage.
- Yellow unbanded snails are better camouflaged → at a selective advantage.
- Natural selection favours yellow unbanded snails, which become more common in grassland populations.

🌲 In Non-Uniform Woodland Habitats:
The background is more varied and dappled with shadows.
- Yellow unbanded shells stand out more and are more easily seen → at a selective disadvantage.
- Brown banded shells blend in better with the surroundings → at a selective advantage.
- Natural selection favours brown banded snails, leading to their predominance in woodland environments.

Question 17

what are the different sources of variation

Answer 17

1. (mutation) gene mutation
2. (mutation) chromosomal mutation
3. (sexual reproduction) meiosis
4. (sexual reproduction) fertilisation

Question 18

what does gene mutation cause and how does variation arise from it?

Answer 18

gene mutation: causes a change in DNA / nucleotide sequence of a gene is brought about by deletion, insertion, substitution or inversion of one or several nucleotides
- gene mutation is the only source that produces **new alleles ** ( variants of the same gene)
- this increases the size of the gene poolfor natural selection to operate on

NOTE: mutations will only have evolutionary impact if they occur in germline cells, causing the mutation to be passed on to the next generation
- germline cells are cells that give rise to gamete
- because a mutation in a somatic cell onyl affects the individual, it is not passed down

Question 19

what is chromosomal mutation and how does variation arise from it?

Answer 19

chromosomal mutation: change in the structure of chromosomes
- ( through duplication, inversion, deletion and translocation) or number of chromosomes ( through non-disjunction) respectively
- chromosomal mutations can lead to loss, duplication or rearrangement of genes that may result in new gene interactions that produce a new phenotype

non-disjunction: chromosomes do not separate correctly
- one gamete may get two copies of a chromosome (extra)
- another gamete may get none (missing)

Question 20

how does (sexual reproduction) meiosis cause a variation in the population?

Answer 20

• meiosis: crossing-over between non-sister chromatids of homologous chromosomes during prophase I and independent assortment of homologous chromosomes in metaphase I lead to new combinations of alleles that can produce new phenotypes

Question 21

how does (sexual reproduction) fertilisation cause variation in the population?

Answer 21

(sexual reproduction) fertilisation: the random mating of individuals of the same species produce progeny with new combinations of alleles at each gene locus
- random fusion of gametes between two mating individuals also increases genetic variation in a population, by producing progeny with different allele combinations

Question 22

what is neutral variation and what is the result of it?

Answer 22

• neutral variations/ alleles are genetic variations/ alleles which do not alter the ability of an individual to survive and reproduce
• they neither confer a selective advantage nor disadvantage to the individual
• since neutral variations will not come under selection pressure nor natural selection, they will be preserved in a population

for example,
- much of the DNA in eukaryotes is DNA which does not code for a protein or RNA.
- Hence, variation in non-coding DNA are neutral as they do not affect the phenotype of the organism and hence do not affect the reproductive success of the individuals
- some variations that occur in the coding region of DNA may also be neutral because of the degenerate code. a change in a nucleotide may still lead to the same amino acid coded, hence there is no change in the protein synthesised, hence no effect on the
phenotype.
- Some variations that occur in the coding regions of DNA may lead to a change in amino
acid(s). However, they have no selective effect as they do not occur in the essential regions
of the proteins (e.g. in active site, binding sites). These variations do not affect protein
structure and function and hence do not affect fitness of the individual.

Question 23

what is the importance of variation in selection?

Answer 23

• natural selection relies on variation to exist in a population before its effect can be exhibited
  ( genetic variation results in phenotypic variation among organisms within the same population. this makes different phenotypes available for selection, so that under a selection pressure, some phenotypes confer a selective advantage to certain individuals, while others confer a selective advantage to other individuals)
• if population of individuals is genetically identical, selection would have no effect, because all the phenotypes are essentially the same and the selection pressure acts equally on all individuals
• populations that are genetically varied will be able to adapt to changing environmental conditions better than those that are genetically identical

Question 24

how does natural selection influence the distribution of alleles in a population? and what are the three selection trends?

Answer 24

• natural selection can affect the frequency of a heritable trait in a population in three ways
  > depending on which phenotypes in a varying population are favoured, and how common these phenotypes are in the population

the three selection trends:
1. directional selection
2. disruptive selection
3. stabilising selection

Question 25

what does directional selection favour and what is it?

Answer 25

**directional selection**: favours individuals with initially rare phenotypes - the selection operates **against one extreme** of the range of variations of a particular characteristic (this variation is selected against) - it causes the frequency curve for variations in the phenotype to shift towards the opposite extreme ( this extreme variation is selected for) - directional selection is most common during periods of environmental change, or when members of a population migrate to a new habitat with different environmental conditions example: development of antibiotic resistance in bacteria

Question 26

what is disruptive selection?

Answer 26

**disruptive selection**: occurs when environmental conditions are varied in a way that favours individuals **on both extremes** on a range of phenotypes - the selection operates **against the middle range of variation** in a particular characteristic - over several generations, diversifying selection will result in one population splitting into **two sub-populations with different ecological niches**

Question 27

what is stabilising selection?

Answer 27

stabilising selection: operates when a phenotype is in equilibrium with the environmental conditions - this selection operates against both extremes within a population - it results in the **continual elimination of individuals with extreme variation** - this causes the frequency of the intermediate phenotype to increase

Question 28

why is a population the smallest unit that can evolve?

Answer 28

- a population is the smallest unit that can evolve. An individual cannot evolve. - evolution is the measure of change in allele frequency in a population's gene pool through many generations - a population is a group of many individuals representing phenotypic variations ( due to genetic differences) living in the same niche at the same time - an individual is genetically identical throughout its lifetime > it cannot change its genes in response to environmental pressures - therefore an individual cannot evolve - natural selection acts on individuals: each organism's combination of traits affects its survival and reproductive success compared to other individuals > however, even though individuals are selected for or against, they themselves do not evolve - Individuals with certain traits may survive and reproduce better (or worse), which means they contribute differently to the next generation. ↳ An individual that reproduces successfully passes on its alleles to the next generation. ↳ An individual that fails to reproduce removes its alleles from the population. - Over time, differential reproductive success leads to changes in allele frequencies in the population. ↳ This is the evolutionary effect of natural selection. - The evolutionary impact of natural selection is only observable when we track how a population’s genetic makeup changes over time — not within a single organism. - As individuals interbreed within the population certain alleles can be passed on to the next generation, this causes changes in allele frequencies over many generations. In contrast, an individual only represents (and is part of) only one generation. Hence, changes in allele frequency cannot be observed.

Question 29

what is frequency dependent selection?

Answer 29

- in this mechanism, the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population - survival and reproduction of one phenotype increases if that phenotypic form becomes less common in the population, because natural selection favours the phenotype which is least common

Question 30

what is heterozygote advantage?

Answer 30

- Genetic variability may also be preserved by natural selection, the very same force that generally reduces it. - Balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population.

Question 31

what is sexual selection? and what are the the two types of sexual selection?

Answer 31

- sexual selection is a form of natural selection in which individuals with certain characteristics are more likely than other individual to obtain mates - sexual selection can result in sexual dimorphism - males and females of an animal species have different reproductive organs - they may also show other noticeable differences not directly related to reproduction or survival- called secondary sexual characteristics - this distinction in appearance is called sexual dimorphism can be in the form of male adornment like: - manes on lions - antlers on deers - colourful plumage in birds (males are usually the showier sex) the two types of selection: - intrasexual selection - intersexual selection

Question 32

what is intrasexual selection?

Answer 32

- intrasexual selection is a type of sexual selection within the same sex, more often the males - secondary sex structures may be used to compete with members of the same sex for mates - contests may involve physical combat, but are more often ritualised displays - intrasexual selection is common in species where the winning individual garners a harem of mates harem: a group of females

Question 33

what is intersexual selection?

Answer 33

- intersexual selection or mate choice is a more common type of sexual selection - individuals of one sex (usually females) are choosy in selecting their mates - mates with the largest or most colourful adornments are often most attractive to females - every time a female chooses the traits that caused her to make that choice of mate - this allows a male mate with that particular phenotype to perpetuate his alleles

Question 34

what is the advantage to females of being choosy?

Answer 34

- one hypothesis is that females prefer male traits that are correlated with ' good genes' - in several bird species, research has shown that traits preferred by females like bright beaks or long tails, are related to overall male health - female frogs prefer to mate with males that give long mating calls and research ahs shown that the duration of a male's mating call is indicative of the male's overall genetic quality

Question 35

what is the definition of genetic drift?

Answer 35

- genetic drift refers to random changes in allele frequencies in small population from one generation to the next due to chance events (rather than natural selection) (genetic drift is not driven by usefulness, its random, not purposeful)

Question 36

when does genetic drift usually occur?

Answer 36

- while genetic drift can occur in populations of any size, it effects are more pronounced in small populations - this is because the alleles present in the gene pool only represent a small proportion of the alleles present in the ancestral/ parent population's gene pool - changes in the allele frequency are caused by random sampling of gametes from a small number of reproducing individuals - these changes occur purely by chance, regardless of whether an allele is beneficial or harmful - in a small population, it is more likely that an allele present at a low frequency in the population could be completely lost ( allele freq becomes 0) or become fixed ( allele freq = 1) by chance in the population

Question 37

what is the significance of genetic drift?

Answer 37

- genetic drift can cause alleles that encode harmful traits to become fixed and alleles that encode advantageous traits to become lost by chance - these act quickly to reduce genetic variation in small populations - survival of individuals may not be the result of possessing best-fit phenotypes, and the population does not become better adapted to its environment - as a result, the population's survival can be threatened since the population is not well-adapted to changing environmental conditions

Question 38

what are the two examples of the impact that genetic drift has on the population?

Answer 38

- bottleneck effect - founders effect

Question 39

GENETIC DRIFT what is the bottleneck effect?

Answer 39

- bottleneck effect occurs when a population is drastically reduced in size due to sudden drastic events eg. fire or flood - by chance, certain alleles may be over-represented among the survivors, others may be under-represented and some may be absent all together - bottleneck effect results in a reduction of genetic variation in the surviving population compared to the original population - genetic drift will continue to have substantial effect on the gene pool until the population becomes large enough such that chance event are less significant - Moreover, even when the population that has passed through a bottleneck ultimately recovers in size - it may have low genetic variation in its gene pool for a long period of time

Question 40

GENETIC DRIFT what is the founder effect?

Answer 40

- the founder effect occurs when a few individuals become isolated from a larger population due to chance events - the smaller group may establish a new population who only has a small proportion of alleles from the gene pool of the original population - by chance, certain alleles may be over-represented in the isolated population while others may be under-represented and some may be absent all together - founder effect results in a reduction in genetic variation in the isolated population compared to the original population - genetic drift will continue to affect the gene pool of the isolated population until it becomes larger

Question 41

what does gene flow refer to?

Answer 41

- gene flow refers to the movement of alleles from one population to another as a result of interbreeding between members of the two populations - gene flow tends to decrease the genetic variation between the two populations because alleles are exchanged between the populations

Question 42

why does natural selection not create perfect organisms?

Answer 42

1. natural selection can only act on existing variations - natural selection only works with traits that already exist in the population - it cannot create new traits on demand - mutations that lead to new alleles occur randomly, not because they are needed - as a result, natural selection selects the best available traits, not necessarily the ideal ones 2. evolution is limited by historical constraints - each species carries the evolutionary legacy of its ancestors - Evolution modifies existing structures rather than building new ones from scratch. - It works by adapting what’s already there to serve new functions. 3. Adaptations are often compromises - Organisms must perform multiple functions, so adaptations often involve trade-offs. - A trait that improves one ability may reduce another. eg. Seals have flippers for swimming, which makes them efficient in water but clumsy on land — a compromise between two environments. 4. chance, natural selection, and the environment interact - Random events (e.g. storms, natural disasters) can influence which individuals survive and reproduce, regardless of their fitness. - This means that evolution can be affected by luck, not just selection. - The environment is also constantly changing, so what is beneficial today may not be tomorrow.

Question 43

STABILISING SELECTION - what is the environment like for this selection? - what is the selection pressure of this against? - this environment favours individuals with what kind of phenotype? - what are the effects of this selection?

Answer 43

- the environment being constant over time leads to stabilising selection - the selection pressure is against both extremes of the phenotypic distribution - this selection favours individuals with intermediate phenotypes - effect: often associated with a population that is well-adapted to its environment - this reduces variation within the population, maintaining the constancy of species over generations example: infants born with intermediate weights are most likely to survive - infants at either extremes, too small or too large, have higher rates of mortality - stabilising selection operates to reduce variability in birth weight so it is close to the weight with the minimum mortality rate

Question 44

DISRUPTIVE SELECTION - what is the environment like for this selection? - what is the selection pressure of this against? - this environment favours individuals with what kind of phenotype? - what are the effects of this selection?

Answer 44

- when there are extreme and drastic changes, directional selection occurs - the intermediate range of the phenotypic distribution is selected against - and the individuals with extreme phenotypes are favoured effect: this results in divergence, causing emergence of distinct groups of individuals (sub-species) within the population example: when a new predator is introduced to a lake with fishes, the small sized fish can hide in crevices while the large sized fish can swim away quickly enough - it is the medium sized fish which are preyed upon

Question 45

what is the biological concept of species?

Answer 45

definition: a species is a group of organisms that are able to interbreed with one another in nature to produce VIABLE and FERTILE offspring features: - it emphasises the importance of reproductive isolation and the absence of gene flow in the formation of a species - it is useful to distinguish different species that may be morphologically similar limitations: cannot be used to classify all organisms: - cannot be applied to asexual organisms - cannot be applied to fossils since there is no way to check interbreeding in extinct forms

Question 46

DIRECTIONAL SELECTION - what is the environment like for this selection? - what is the selection pressure of this against? - this environment favours individuals with what kind of phenotype? - what are the effects of this selection?

Answer 46

- when the environment changes over time, directional selection tends to occur - the selection pressure is against one extreme of the phenotypic distribution - and individuals with the other extreme phenotype are favoured effect: over successive generations, one phenotype gradually replaces another and could possibly lead to the emergence of new species example: seeds declined and large heavy seeds became finches’ primary source of food. Many finches died and most of the survivors were large birds whose beaks were larger and deeper and able to crack large seeds. In a few generations, these larger birds became more common in the population. Hence, during the drought, natural selection operated in favour of the larger phenotype.

Question 47

what is the ecological concept of species?

Answer 47

definition: a species is a group of organisms that share the same ecological niche features: - the more similar the two organisms are, the more likely their needs will overlap, the more likely they will compete - and therefore more likely that they are of the same species - this concept shows how natural selection helps species survive by adapting to reduce competition with others in their environment - can be applied to asexual and sexual species limitations: - difficult to determine the degree to which two or more individuals are competing ecologically

Question 48

what is the morphological concept of species?

Answer 48

definition: a species is a group of organisms that have the same body shape/ form and other structural features features: - useful for classifying organisms where information on gene flow is not availible - can be applied to asexual and sexual species, and fossils limitations: - Definition relies on subjective criteria: researchers may disagree on which key structural features distinguish a species. - Difficult to quantify how much morphological differences define a different species. - Organisms in the same species may look very different depending on their gender or stage of life cycle. - Organisms which are not related may have similar structures due to convergent evolution

Question 49

what is the genetic concept of species?

Answer 49

definition: it is a group of genetically compatible and interbreeding natural populations that are genetically isolated from other such groups features: - mainly based on comparing DNA sequences - it is distinguished from the biological species concept by its focus on genetic isolation rather than reproductive isolation - Two different species have different DNA (different gene pools), and these genetic differences prevent them from mixing — so they don’t interbreed naturally. - Their gene pools stay separate (or "protected") because they are too genetically different to produce fertile offspring. limitations: - cannot be applied to asexual organisms - cannot be applied to fossils since there is no way to check interbreeding in extinct forms - difficult to determine the degree of genetic difference required to indicate separate species

Question 50

what is the phylogenetic concept of species?

Answer 50

definition: A species is the smallest group of organisms that share a common ancestor, forming one branch on the tree of life. features: - Evolutionary history of a species is traced by comparing various characteristics (e.g. morphology/ molecular sequence) with those of other organisms. limitations: -There might be limited data to determine phylogeny of certain organisms. - Difficult to determine the degree of difference required to indicate separate species.

Question 51

what are reproductive barriers? and what are the two types of reproductive barriers?

Answer 51

- reproductive barriers/ reproductive isolating mechanisms are biological barriers that prevent interbreeding between closely related species when their ranges (area where each live) overlap. - Reproductive barriers preserve the gene pool of each species reproductive barriers can be categorised into: - pre-zygotic barriers: are barriers that prevent fertilisation from occuring - post-zygotic barriers: barriers that prevent the hybrid-zygote from developing into viable fertile adult

Question 52

what is speciation? and what are the two types?

Answer 52

- speciation: is the process by which one species splits into two or more species > it is the evolution of a new species - for a new species to be formed, a population of the same species must be first reproductively isolated such that no gene flow occurs between the isolated population and the ancestral (main) population - speciation can occur in two main ways > allopatric speciation > sympatric speciation - depending on how gene flow is interrupted between populations of the existing species

Question 53

what is allopatric speciation?

Answer 53

- speciation that occurs when one population becomes geographically separated from the rest of the population, causing disruption of gene flow between two sub populations from the rest of the population, causing disruption of gene flow between the two sub-populations

Question 54

process of allopatric speciation: 1. ____ ____ occurs, where the ancestral population is ___ into two or more sub-populations by ____ ____ 2. members of the sub-populations are prevented from ____ as they do not meet. - ____ ____ between the sub-populations does not occur 3. each sub-population ____ its own mutations - natural selection also occurs ____ in the different sub-populations because the different environmental conditions encountered exert different ____ ____ in these sub-populations - different traits are ____ ____ and different traits are at a selective advantage - hence, each sub-population ____ in response to the different selection pressures of the different environments 4. genetic ___ may also take place independently to alter ____ ____ in each sub-population 5. over time, allele frequencies int he sub-populations are altered differently - genetic ____ between the gene pools of the sub-population increases - gene pools ____ 6. Each sub-population then separately evolves ____ ____ ____ such as mechanical, gametic and behavioural barriers. 7. over time, when the geographical barrier is removed, the two populations can no longer ____ to produce ____ and ____ offspring - therefore speciation has occured

Answer 54

1. GEOGRAPHICAL SEPARATION/ ISOLATION occurs, where the ancestral population is DIVIDED into two or more sub-populations by GEOGRAPHICAL BARRIERS 2. members of the sub-populations are prevented from MATING as they do not meet. - GENE FLOW between the sub-populations does not occur 3. each sub-population ACCUMULATES its own mutations - natural selection also occurs INDEPENDENTLY in the different sub-populations because the different environmental conditions encountered exert different SELECTION PRESSURES in these sub-populations - different traits are SELECTED FOR and different traits are at a selective advantage - hence, each sub-population ADAPTS in response to the different selection pressures of the different environments 4. genetic DRIFT may also take place independently to alter ALLELE FREQUENCY in each sub-population 5. over time, allele frequencies int he sub-populations are altered differently - genetic DIFFERENCES between the gene pools of the sub-population increases - gene pools DIVERGE 6. Each sub-population then separately evolves REPRODUCTIVE ISOLATION MECHANISMS such as mechanical, gametic and behavioural barriers. 7. over time, when the geographical barrier is removed, the two populations can no longer INTERBREED to produce VIABLE and FERTILE offspring - therefore speciation has occured

Question 55

what is sympatric speciation and what is it more common in?

Answer 55

- speciation that occurs in populations that live in the same geographic region - sympatric speciation does not involve geographical barriers - instead, reproductive isolation mechanisms occur at the start of the speciation process to prevent gene flow between two sub-populations int he same geographical region - sympatric speciation is especially common in plants

Question 56

sympatric speciation can occur if gene flow is reduced by isolation mechanisms such as?

Answer 56

physiological isolation 1. polyploidy 2. habitat differentiation behavioral isolation 3. sexual selection

Question 57

what is polyploidy and what are the two kinds of polyploidy?

Answer 57

- Polyploidy is the possession of extra sets of chromosomes. - Polyploid speciation occurs with a change in chromosome number. It is far more common in plants than in animals. - There are two kinds of polyploidy: Autopolyploidy and Allopolyploidy

Question 58

polyploidy: what is autoploidy?

Answer 58

- An autopolyploid is an individual that has extra chromosomal sets that are all derived from a single species. - Autopolyploid speciation happens when cells double their chromosomes but do not divide during mitosis or meiosis. - The polyploid can undergo self-fertilisation to produce viable and fertile offspring - while at the same time, it cannot interbreed with the parental population to produce fertile offspring due to differences in chromosome numbers. - This forms a new species.

Question 59

polyploidy: what is alloploidy?

Answer 59

- Allopolyploidy occurs when two different species interbreed and produce a hybrid. - The hybrid ends up with extra sets of chromosomes from both parent species. why are hybrids sterile? - During meiosis, chromosomes must pair up - with their homologous partners. But in hybrids, the chromosomes from the two different species are not homologous, so they can’t pair up properly. - This causes meiosis to fail, making the hybrid sterile (unable to produce gametes). how can the hybrid become fertile? - Sometimes, an error in mitosis causes the chromosome number to double. - Now, each chromosome has a homologous pair, allowing meiosis to occur normally. - The hybrid becomes fertile and can reproduce with others like itself. result: - The fertile hybrid is now reproductively isolated from both original parent species (due to different chromosome numbers). - Since it cannot breed with either parent species but can breed with others like itself, it is considered a new species.

Question 60

how does habitat differentiation lead to sympatric speciation?

Answer 60

- Sympatric speciation occurs when variation enables a sub-population to exploit a habitat or resource not previously used by the ancestral population, resulting in reproduction isolation mechanisms that prevent gene flow between the new and ancestral population.

Question 61

how can sexual selection lead to sympatric speciation?

Answer 61

- Sympatric speciation can occur when mate choice creates a reproductive barrier that prevents gene flow. - In Lake Victoria, two sympatric cichlid species — Pundamilia pundamilia (blue-tinged males) and Pundamilia nyererei (red-tinged males) — were studied. - Females of each species strongly preferred males of their own species based on breeding coloration. This mate preference prevented interbreeding and maintained reproductive isolation, suggesting sexual selection was a key factor in speciation.