Lecture 21 (Population genetics and natural selection)

Question 1

Evolution

Answer 1

Genetic changes in a population over time

Populations evolve, individuals don’t

Question 2

Population

Answer 2

Localised group of individuals of the same species

Question 3

Gene pool

Answer 3

Total aggregate of genes (and their alleles) in the population at one time

Question 4

Why might we need to estimate frequencies of genotypes in a population?

Answer 4

To predict how many individuals will inherit a genetic disease

To estimate the proportion of individuals who are ‘carriers’ of a genetic disease

Question 5

How do we predict genotypes in a population?

Answer 5

Hardy-Weinburg equation
Allele frequency
p+q=1

p^2+2pq+q^2 =1 (this equation shows that there are only three genotypes)

Question 6

Allele frequencies change via…

Answer 6

Non-random mating (no choice) - assortive mating or inbreeding 
Random genetic drift 
Bottleneck effect 
Founder effect 
Natural selection 
Gene flow or migration 
Mutation

Question 7

Assortative mating and interbreeding

Answer 7

Assortative mating - a mating pattern and form of sexual selection in which individuals with similar phenotypes mate with one another more frequently than would be expected under a random mating pattern.
Inbreeding - production of offspring from the mating or breeding of individuals or organisms that are closely related genetically.

Question 8

Random genetic drift

Answer 8

A random change in allele frequencies due to sampling errors over generations

the change in allele frequencies due to accumulated effects of chance (random) over successive generations

Question 9

Non random mating vs random mating

Answer 9

Nonrandom mating occurs when the probability that two individuals in a population will mate is not the same for all possible pairs of individuals. When the probability is the same, then individuals are just as likely to mate with distant relatives as with close relatives – this is random mating.

Question 10

The bottleneck effect

Answer 10

where a large population suddenly reduces in size (catastrophe or human impact)

Only a few individuals survive so some alleles may become underrepresented or removed all together (allele frequencies change)

Question 11

The founder effect

Answer 11

the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.

Tends to be reduced genetic variation in the new, founding population (it is a type of boatneck event almost) (therefore changes allele frequencies)

Question 12

Three types of selection

Answer 12

Same species but selecting for different phenotypes

Stabilising, directional and disruptive selection

Question 13

Stabilising selection

Answer 13

Extreme phenotypes are selected against // Favours the average, tends to prevent evolutionary change

Reduces variation but does not change the mean

Question 14

Example of stabilising selection

Answer 14

Babies - medium sized baby is good because you want them to be big enough to be healthy and small enough to be delivered

Question 15

Directional selection

Answer 15

A single end of distribution curve is selected for and allele frequency shifts in one direction, results in evolutionary change

This type of selection changes the mean value towards one extreme

Question 16

Directional selection example

Answer 16

Giraffes - being taller is more favourable as taller giraffes can eat things that are higher up

Question 17

Disruptive selection

Answer 17

Both extremes are selected for, average phenotype selected against

This selection favours the two extremes producing two peaks

Question 18

Sexual selection

Answer 18

Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex.

Question 19

Frequency dependent selection

Answer 19

Frequency-dependent selection is an evolutionary process by which the fitness of a phenotype or genotype depends on the phenotype or genotype composition of a given population.

This type of selection is based on whether something is rare or common in a population

You get fluctuations between one type of the species being more common to the other becoming more rare. You get an advantage by being rare but the better you do the less rare you become ( a constant cycle between the frequency of the different phenotypes in the same species)

Question 20

Cline

Answer 20

a gradient of variation, often because a species extends across a geographical range

The gradual geographic change in genotypic/phenotypic composition is termed a cline

Question 21

Mutation

Answer 21

permanent changes in the base sequence of DNA.

Mutations create new alleles and therefore new phenotypes. They may become more common in a population if they provide a survival or reproductive advantage in the current environment.

Very slow to act and usually disadvantageous, its role is usually of macroevolutionary proportions

Question 22

Migration

Answer 22

An individual from another population successfully mates (contributes gametes) to the gene pool

Brings new alleles
Changes proportions of existing alleles
Changes population size
Makes two populations more similar

Question 23

Natural selection

Answer 23

Where some phenotypes have the advantage in a certain environment, so individuals with that phenotype are more likely to survive, reproduce and pass on their alleles the next generation.

Question 24

Gene flow (migration)

Answer 24

The ability of alleles to enter or leave a population.