Week 4: Evolutionary Genetics and Why it Matters to Natural Processes

Question 1

List the 6 types of selection

Answer 1

1. Disruptive
2. Directional
3. Stabilising
4. Balancing
5. Intrasexual
6. Intersexual

Question 2

Describe disruptive selection

Answer 2

• Leads to a U-shaped distribution
• Favours distribution extremes
• Does not favour intermediate forms

Question 3

Describe directional selection

Answer 3

• Skewed distribution

- Favours one end of distribution thus directs selection towards that end

Question 4

Describe stabilising distribution

Answer 4

• Selection occurs against extremes and favours functional intermediates
• E.g. not too small or too big - the intermediate is favoured and population size thus stabilised
• Effect of environment but also the organisms own physiology

Question 5

Describe balancing selection

Answer 5

Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone.

Question 6

Describe Intrasexual selection

Answer 6

• Selection within the same sex of a species

- E.g. larger males have greater success reproducing and are thus selected for

Question 7

Describe intersexual selection

Answer 7

• Forced selection due to effect of one sex on another

- E.g. female birds prefer males of a certain colour and thus that colour is selected for

Question 8

What are the 2 sources of genetic variation?

Answer 8

1. Mutation

2. Recombination

Question 9

What is genetic drift?

Answer 9

Variation in the relative frequency of a genotype/allele in a small population

Question 10

Does genetic drift have a greater effect on large or small population?

Answer 10

Small populations

Question 11

Why does genetic drift have greater effect in small populations?

Answer 11

With fewer individuals; which individuals mate can have larger effect on the small population

Question 12

What is likely to happen to a neutral allele in small and large populations?

Answer 12

In a small population - the allele will either reach extinction or fixation
In a large population - the allele will most likely reach fixation but not extinction

Question 13

The 5 conditions of the Harvey-Weinberg equilibrium:

Answer 13

1. There can be no differences in the reproduction and survival rates of individuals in a population
2. Populations must not be added to or subtracted from due to migration
3. There can be no mutation
4. The population must be sufficiently large
5. Individuals must mate at random

Question 14

What is a founder effect?

Answer 14

Low genetic variation occurring due to the population being descended from a small number of founders

Question 15

What is gene flow?

Answer 15

The movement of genetic material from one population to another
E.g. migration
If gene flow is high enough, populations will become equivalent and subsequently considered as 1 population

Question 16

What is the bottleneck effect?

Answer 16

An occurrence due to a significant reduction in a population’s size that results in extreme genetic drift