7.3 Evolution and speciation Flashcards

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1
Q

define variation

A

the differences that exist between individuals in a population, this is mostly due to different allele combinations producing different phenotypes

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2
Q

define selection pressures giving 3 examples

A

where organisms die or fail to reproduce
- predation
- disease
- competition for resources

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3
Q

model 6 marker on how new species is formed

A
  1. geographical location
  2. separate gene pools
  3. variation due to mutation
  4. different biotic and abiotic conditions
  5. different reproductive success (advantage) so they survive
  6. Leads to changes in allele frequency as they reproduce and new generations inherit these genes
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4
Q

describe stabilising selection

A

individuals with characteristics towards the middle are more likely to survive and reproduce

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5
Q

when does stabilising selection occur

A

when the environment isn’t changing

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6
Q

what happens to the mean and range in stabilising selection

A

the mean stays in the middle but the range of phenotypes is reduced

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7
Q

describe directional selection

A

individuals with alleles for a single extreme phenotype are more likely to survive and reproduce

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8
Q

when does directional selection occur

A

change in environment

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9
Q

what happens to the mean and range in directional selection

A

means move in a direction away from the original

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10
Q

describe disruptive selection

A

individuals with alleles for extreme phenotypes are more likely to survive and reproduce

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11
Q

when does disruptive selection occur

A

in fluctuating environments which favour more than one phenotype

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12
Q

what happens to the mean and range in disruptive selection

A

mean in the middle decreases and the range increases

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13
Q

define speciation

A

when a new species arises from an existing species due to certain conditions

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14
Q

when does speciation occur

A

when populations of the same species become reproductively isolated from each other so can no longer interbreed to produce fertile offspring

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15
Q

5 steps of allopatric speciation

A
  • geographical isolation so no interbreeding hence separate gene pool
  • different environmental conditions can occur causing the populations to be affected by different selection pressures
  • different mutations will occur so different advantageous alleles arise
  • this leads to a change in the allele frequency
  • eventually phenotype frequencies change and the populations become reproductively isolated
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16
Q

5 steps of sympatric speciation

A
  • formation of a new species from a population without geographical isolation
  • random mutation or change in behaviour prevents individuals from breeding with each other
  • so no interbreeding
  • over time the reproductive isolation leads to a change in allele frequency in the different populations
  • eventually different phenotype frequencies change
17
Q

what are the three changes which can cause reproductive isolation

A

temporal changes - different breeding seasons / different feeding times
mechanical changes - physical mismatch of reproductive parts / gamete incompatibility such as sperm killed in females tract
behavioural changes - different courtship displays such as change in song so no attraction

18
Q

3 steps of genetic drift

A
  1. individuals in a population show variation in genotypes
  2. by chance an allele for one genotype is passed on to more offspring than the others, so the number of individuals with this allele increases in frequency in the population
  3. if by chance this same alley is passed on more often over repeated generations then this can leads to evolution as the allele changes in frequency in the population