Natural selection (lec 5) Flashcards

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1
Q

Population structure effect on variation

A

-migration between populations (gene flow)
-isolation of populations makes them more distinct
size of population and amount of gene flow will determine evolutionary outcomes

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2
Q

Disruptive selection

A
  • diversifying

- homozygotes fitter than heterozygotes or multiple variants favoured

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3
Q

Positive selection:

A
  • eg. capsid proteins of viruses
  • difficulty developing vaccine due to changing coats to avoid immune system (red queen)
  • mutations in the sites that the host immune system recognise are under positive selection
  • recognition sites thus change v rapidly
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4
Q

Purifying selection

A

eg capsid proteins of viruses

  • some parts of virus can’t tolerate changes as they are necessary to maintain structure or functions
  • these regions are under purifying selection, show few changes
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5
Q

In reality most genes probably experience a mix of both:

A

-purifying and positive selection

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6
Q

Balancing selection

-e.g. sickle cell anaemia gene for malarial resistance

A
  • multiple variants are favoured
  • results in maintenance of high levels of polymorphism
  • often because different alleles are favoured in different circumstances or because theres an advantage to being different (frequency-dependent selection)
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7
Q

Frequency-dependent selection (balancing selection)

A

e. g. MHC

- heterozygotes have an advantage

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8
Q

Inbreeding vs outcrossing (reproductive advantage)

A
  • inbreeding increases homozygosity
  • recessive alleles persisting in populations brought out into the phenotype due to inbreeding
  • inbreeding depression - reduced fitness
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9
Q

Inbreeding could be an advantage to not breaking up

A

co adapted gene complexes

-after a period of inbreeding, negative deleterious mutations purged so no inbreeding depression, as long as environment remains the same

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10
Q

Outbreeding can lead to

A

heterozygote advantage
-also called heterosis or hybrid vigour
eg, Soay sheep in Hebrides
-higher fitness sheep have higher levels of heterozygosity

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11
Q

Outbreeding depression=

A
  • organisms well adapted to an environment mate with individuals adapted to another environment
  • eg conservation genetics and captive breeding
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12
Q

Purging

A

-individuals that sirvive have gotten rid of the nastiest deleterious recessive mutations

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13
Q

Assortative mating

A

-can ensure that similarly adapted individuals mate

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14
Q

Dis-assortative mating

A

-can ensure individuals mate with genetically different individuals to increase genetic diversity

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15
Q

Kin recognition

A

-behavioural recognition of close relatives

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16
Q

inbreeding avoidance

A

-recognition associated with MHC

17
Q

Self-incompatibility in plants

-type of frequency-dependent selection

A
  • genetically controlled

- pollen with similar genotype to that expressed on stigma not allowed to fertilise

18
Q

Hardy-Weinberg equilibrium HWE 1908

A
  • forces affecting variation are tested

- many assumptions used to develop models to test hypotheses about polymorphisms in populations

19
Q

genotype frequencies

A

p2 + 2pq + q2 = 1

20
Q

Allele frequencies

A

p + q = 1