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From Organisms to Ecosystems - Lectures > Lecture 18. Fitness and Selection > Flashcards

Lecture 18. Fitness and Selection Flashcards

1
Q

What is fitness ?

A

The ability to survive and reproduce

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2
Q

What must successful phenotypes be ?

A

Viable and fertile

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3
Q

How is fitness measured ?

A

As the total number of offspring or alleles an individual contributes to the next generation

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4
Q

What is the absolute fitness ?

A

A measure of the total number of offspring or alleles that individuals contribute to the generation

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5
Q

How do we measure relative fitness ?

A

Compare each individuals absolute fitness to a benchmark value

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6
Q

How do we measure genotype fitness ?

A

Calculate the average number of offspring left by individuals with each genotype

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7
Q

What is the relative contribution of a genotype a product of ?

A

Its frequency and relative fitness

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8
Q

What are the effects of selection on phenotype ?

A
  1. Phenotype distribution
  2. Genotype frequencies at a single loci
  3. New alleles
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9
Q

What are the three types of selection ?

A
  1. Stabilising selection
  2. Directional selection
  3. Disruptive selection
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10
Q

In directional selection (Dominant >= heterozygote >= recessive), what do two homozygotes have ?

A

Different fitnesses

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11
Q

In directional selection (Dominant >= heterozygote >= recessive), what does the heterozygote have ?

A

Either an intermediate fitness or a fitness equal to one of the homozygotes

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12
Q

In directional selection (Dominant >= heterozygote >= recessive), what does it result in ?

A

An increase in frequency of one allele at the expense of the other

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13
Q

What is the advantageous allele ?

A

An increase in frequency of one allele at the expense of the other

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14
Q

In directional selection (Dominant >= heterozygote >= recessive), what can it be a mechanism of ?

A

Directional or stabilising phenotypic selection, depending on whether the advantageous allele is a new mutation

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15
Q

In directional selection (Dominant >= heterozygote >= recessive), when does the rate of allele frequency change ?

A

Depending on starting frequencies and the fitness of the heterozygote

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16
Q

In directional selection (AA = Aa > aa), what does the heterozygote genotype have ?

A

The same fitness as the fitter homozygote

17
Q

In directional selection (AA = Aa > aa), what happens when the advantageous allele is at low frequencies ?

A

It occurs mostly in heterozygotes where it can be selected for. This results in a rapid increase in frequency

18
Q

In directional selection (AA = Aa > aa), where do high frequencies in the deleterious allele occur ?

A

Mostly in heterozygotes and cannot be selected against which slows down the rate of frequency change for the advantageous allele

19
Q

In directional selection (AA = Aa < aa), what does the heterozygote genotype have ?

A

The same fitness as the less fit homozygote

20
Q

In directional selection (AA = Aa < aa), when the advantageous allele is at low frequencies where does it occur ?

A

Mostly in heterozygotes where it cannot be selected for resulting in a slow increase in frequency

21
Q

In directional selection (AA = Aa < aa), what happens to high frequency homozygote recessive genotypes ?

A

They become more frequent and can be selected for which speeds up the rate of change

22
Q

AA > Aa > aa

A

Advantageous allele is co-dominant or incompletely dominant

23
Q

AA > Aa < aa

A

Underdominance

24
Q

AA > Aa < aa, what type of fitness does the heterozygote have ?

A

The lowest fitness

25
Q

In directional selection (AA = Aa > aa), what does this result in ?

A

Unstable equilibrium

26
Q

In directional selection (AA = Aa > aa), what type of mechanism is this ?

A

Disruptive selection

27
Q

AA > Aa < aa

A

Underdominance

28
Q

AA < Aa > aa what type of fitness is this ?

A

The heterozygote has the highest fitness and results in maintenance of both alleles

29
Q

In directional selection (AA = Aa > aa), what type of mechanism is this ?

A

Stabilising selection

30
Q

AA < Aa > aa

A

Heterozygote advantage or overdominance

31
Q

AA < Aa > aa, what is an example ?

A

Sickle cell anaemia

32
Q

AA > Aa > aa

A

Negative frequency dependent selection

33
Q

AA > Aa > aa what happens to the fitness ?

A

It decreases as it becomes more common

34
Q

What is a neutral allele ?

A

Have no effect on the organisms fitness and are invisible for selection and is determined by drift

35
Q

What is purifying or negative selection ?

A

If new alleles at a locus are deleterious, selection will act to remoe them

36
Q

What is positive selection or adaptive evolution ?

A

If a new allele at a locus is advantageous, it will act to increase its frequency

37
Q

What are two major drivers of positive selection ?

A
  1. Diet and nutrients

2. Infectious disease ad immunity

From Organisms to Ecosystems - Lectures (37 decks)

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