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2nd Year: Evolutionary Genetics > Selection at a single locus > Flashcards

Flashcards in Selection at a single locus Deck (41)
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1
Q

Define population genetics.

A

The study of variation within a population over the generations.

2
Q

Define quantitative genetics.

A

The study of quantitative (measurable) characters and their contribution to specific phenotypes.

3
Q

Where is quantitative genetics most widely used?

A

In selective breeding.

4
Q

Define phylogenetics.

A

The study of long-term evolution where changes to DNA become fixed and lead to speciation.

5
Q

What are the 2 main forces acting in population genetics?

A
  1. Selection

2. Stochasticity

6
Q

What is meant by natural selection?

A

Disparities in fitness between geno/phenotypes.

7
Q

What is meant by sexual selection?

A

Male-male competition and female mate choice.

8
Q

What does stochasticity mean?

A

Variation.

9
Q

Define genetic drift.

A

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

10
Q

Does genetic drift create variation?

A

Yes.

11
Q

Define a continuous trait.

A

One that can have any numerical value across an infinite scale.

12
Q

What kind of distribution do continuous traits have?

A

Normal distribution.

13
Q

Define a discontinuous trait.

A

One that can only fit into discrete categories.

14
Q

How many loci are involved in continuous traits? What is the effect of each of these loci?

A

Multiple loci are involved each with a small effect on the phenotype.

15
Q

How many loci are involved in discontinuous traits? What is the effect of each of these loci?

A

Few or a single loci is involved with a large effect on the phenotype.

16
Q

Give a famous example of a population genetics study?

A

The peppered moth.

17
Q

What is biston betularia?

A

The peppered moth.

18
Q

What are the 2 forms of biston betularia?

A

Typica (white) and carbonaria (black).

19
Q

Why did carbonaria become successful?

A

Due to industrial melanism - the black allele proved advantageous during the industrial revolution when the trees were covered with soot.

20
Q

What happened to carbonaria after the Clean Air Act in 1956?

A

It declined.

21
Q

What caused carbonaria?

A

A mutant dominant allele.

22
Q

What is a model?

A

A mathematical representation used to understand a concept.

23
Q

The simplest models are those with ‘non-overlapping generatins’. What kind of life cycle do these organisms have?

A

Birth-survival-reproduction-death.

24
Q

What does ‘w’ represent?

A

Fitness.

25
Q

What is ‘1-s’?

A

The selection coefficient. 1 is the average survival and ‘s’ represents the least-fit genotype.

26
Q

What does w-bar stand for?

A

The average fitness.

27
Q

How do you calculate w-bar?

A

It is the sum of each genotypic frequency multiplied by its fitness value.

28
Q

You can work out the frequency of an allele by using genotypic frequencies. How?

A

The sum of all the genotypic frequencies involving that allele multiplied by their respective fitness values, divided by the average fitness of the population. E.g.
(p2 x p2w) + (pq x pqw)/w-bar

29
Q

When using genotypic frequencies to work out allelic frequency, you halve 2pq. Why?

A

You are trying to work out the frequency of either p or q. 2pq is half p and half q, thus you halve it.

30
Q

Define directional selection.

A

When one (extreme) phenotype is favoured by natural selection.

31
Q

What does ‘h’ represent?

A

The dominance coefficient. It tells you which allele is dominant.

32
Q

If h=0, what does that say about the fitness of 2 genotypes AA and Aa?

A

The fitness of AA and Aa is the same showing A is completely dominant.

33
Q

If h=1, what does that say about the fitness of 2 genotypes AA and Aa?

A

That actually Aa and aa have the same fitness and ‘a’ is dominant instead of A.

34
Q

If h=1/2, what does that say about the fitness of 2 genotypes AA and Aa?

A

There is no dominance between alleles.

35
Q

If 0<1, what does that say about the fitness of 2 genotypes AA and Aa?

A

There is intermediate dominance of A and a.

36
Q

If h<0, what does that say about the fitness of 2 genotypes AA and Aa?

A

There is over-dominance.

37
Q

If h>1, what does that say about the fitness of 2 genotypes AA and Aa?

A

There is under-dominance.

38
Q

Define intermediate dominance. What is another name for it?

A

Whereby both alleles contribute equally to the phenotype, also called co-dominance.

39
Q

Define over-dominance.

A

There is an advantage to being a heterozygote.

40
Q

Define under-dominance.

A

There is a disadvantage to being a heterozygote.

41
Q

List 4 factors that affect allelic frequencies.

A
  1. Migration
  2. Mutation
  3. Sexual selection
  4. Reproductive success