Genetic drift Flashcards Preview

2nd Year: Evolutionary Genetics > Genetic drift > Flashcards

Flashcards in Genetic drift Deck (33)
Loading flashcards...
1
Q

‘The differential survival of genotypes drives evolution’. What does this say about alleles?

A

Frequency is key to diversity and population structure.

2
Q

‘1-s’ is the selection coefficient. What does it say about a particular genotype?

A

That it will survive by proportion less well than others by proportion s.

3
Q

Is it possible for an unfit genotype to survive purely down to luck?

A

Yes, ‘there are always expected deviations from fitness values’.

4
Q

Loci can be either selectively advantageous, disadvantageous or neutral. When they are neutral, what changes in allelic frequency do we expect to see?

A

No changes between generations.

5
Q

Define genetic drift.

A

The chance disappearance of alleles in a small population caused when individuals die or fail to reproduce.

6
Q

Genetic drift drives evolution by creating variation. True or false?

A

True.

7
Q

Why does genetic drift have a bigger effect in small populations?

A

It leads to a loss of diversity or a fixation of genotypes.

8
Q

Consider a single, self-fertilising organism, the smallest population size possible. Explain why small population size leads to a loss of diversity.

A
  1. If the organism is a heterozygote, it will produce 2 different types of gamete.
  2. When the gametes come together, 1/2 will be heterozygous, 1/4 will be homozygous dominant and homozygous recessive.
  3. Thus in one generation, 1/2 of all offspring (the homozygotes) have already lost an allele.
9
Q

If there is no variation there is nothing for selection to act on. True or false?

A

True.

10
Q

What happens when genetic drift acts on large populations? How does this occur?

A

It creates divergence which leads to speciation. Isolated sub-sets of an original population are all exposed to different environments, meaning selection acts on them independently and produces different results.

11
Q

What do genetic drift models assume about mating?

A

It is random.

12
Q

What 2 factors increase genetic drift in a population?

A
  1. Small population size

2. Fewer individuals contributing to reproduction, i.e. species in which males have harems so not all males get to mate

13
Q

What 2 factors reduce drift in a population?

A
  1. Large population size

2. Monogamy, every male gets to mate with a female

14
Q

Is it important to understand the mating systems of organisms when calculating genetic drift?

A

Yes.

15
Q

What is Ne?

A

The ‘effective population size’ coefficient. It refers to the number of organisms in a population that are reproductively active.

16
Q

Ne values are an estimate and can be misleading. Why?

A

Because the Ne values for a small, monogamous population might be the same as a large, random-mating population. Both monogamy and large size reduce drift but small size and random-mating increase it.

17
Q

What is genetic identity?

A

The probability that alleles are identical.

18
Q

What is ‘F’?

A

The inbreeding coefficient, it is a measure of homozygosity WITHIN an individual.

19
Q

What is ‘F’ used to assess?

A

‘Cosanguity’ or the degree of inbreeding in an individual.

20
Q

What is ‘θ’?

A

A measure of coancestry between individuals.

21
Q

What is ‘α’?

A

A measure of coancestry between populations.

22
Q

Fixation indices are used to compare heterozygosity. What is F(IS)?

A

The fixation indice WITHIN a population. F(IS) gives information about inbreeding and assortative mating.

23
Q

How do you calculate F(IS)?

A

F(IS) = [(1- θ) – (1 – F)]/(1- θ)

24
Q

Fixation indices are used to compare heterozygosity. What is F(ST)?

A

The fixation indice BETWEEN populations. F(ST) gives looks at whether there has been differentiation from an orginal population.

25
Q

What does it mean if F(IS) > 0?

A

Homozygosity is greater than expected, there has been inbreeding or assortative mating.

26
Q

What is meant by assortative mating?

A

When individuals preferentially mate with others of a particular genotype.

27
Q

How do you calculate F(ST)?

A

F(ST) = [(1- α) – (1 – θ )]/(1- α)

28
Q

What does it mean if F(ST) > 0?

A

There has been differentiation from a single, original population.

29
Q

What does ‘1 - F’ mean?

A

Observed heterozygosity.

30
Q

What does ‘1 – θ ‘ mean?

A

The average expected heterozygosity within a population.

31
Q

What does ‘1 – α’ mean?

A

The average expected heterozygosity between populations.

32
Q

What can we look at to observe variation within populations? Give 3 examples

A
  1. SNPs
  2. Genetic markers
  3. Mutations in microsatellite regions
33
Q

How can the principles of genetic drift be used to track migration?

A

When a sub-set of the original population leaves and migrates to a new location, diversity is greatly reduced as they carry a low percentage of the total alleles. With each migration there is a reduction in diversity. The least genetically diverse populations are the most recent ones.