Selection at a single locus

Question 1

Define population genetics.

Answer 1

The study of variation within a population over the generations.

Question 2

Define quantitative genetics.

Answer 2

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

Question 3

Where is quantitative genetics most widely used?

Answer 3

In selective breeding.

Question 4

Define phylogenetics.

Answer 4

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

Question 5

What are the 2 main forces acting in population genetics?

Answer 5

1. Selection

2. Stochasticity

Question 6

What is meant by natural selection?

Answer 6

Disparities in fitness between geno/phenotypes.

Question 7

What is meant by sexual selection?

Answer 7

Male-male competition and female mate choice.

Question 8

What does stochasticity mean?

Answer 8

Variation.

Question 9

Define genetic drift.

Answer 9

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

Question 10

Does genetic drift create variation?

Answer 10

Yes.

Question 11

Define a continuous trait.

Answer 11

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

Question 12

What kind of distribution do continuous traits have?

Answer 12

Normal distribution.

Question 13

Define a discontinuous trait.

Answer 13

One that can only fit into discrete categories.

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Give a famous example of a population genetics study?

Answer 16

The peppered moth.

Question 17

What is biston betularia?

Answer 17

The peppered moth.

Question 18

What are the 2 forms of biston betularia?

Answer 18

Typica (white) and carbonaria (black).

Question 19

Why did carbonaria become successful?

Answer 19

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

Question 20

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

Answer 20

It declined.

Question 21

What caused carbonaria?

Answer 21

A mutant dominant allele.

Question 22

What is a model?

Answer 22

A mathematical representation used to understand a concept.

Question 23

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

Answer 23

Birth-survival-reproduction-death.

Question 24

What does ‘w’ represent?

Answer 24

Fitness.

Question 25

What is ‘1-s’?

Answer 25

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

Question 26

What does w-bar stand for?

Answer 26

The average fitness.

Question 27

How do you calculate w-bar?

Answer 27

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

Question 28

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

Answer 28

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

Question 29

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

Answer 29

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

Question 30

Define directional selection.

Answer 30

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

Question 31

What does ‘h’ represent?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

There is no dominance between alleles.

Question 35

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

Answer 35

There is intermediate dominance of A and a.

Question 36

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

Answer 36

There is over-dominance.

Question 37

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

Answer 37

There is under-dominance.

Question 38

Define intermediate dominance. What is another name for it?

Answer 38

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

Question 39

Define over-dominance.

Answer 39

There is an advantage to being a heterozygote.

Question 40

Define under-dominance.

Answer 40

There is a disadvantage to being a heterozygote.

Question 41

List 4 factors that affect allelic frequencies.

Answer 41

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