Topic 2 - Genetic Variation & Drift

Question 1

What is population genetics?

Answer 1

The study of distributions and changes in allele frequency in populations and genetic variation within and among species.

Question 2

Recall the definition of species according to the biological species concept (BSC).

Answer 2

According to the BSC, species are actually or potentially interbreeding populations that are reproductively isolated from other such groups.

Question 3

Define allele frequency

Answer 3

The frequency or proportion of each allele at a given locus within a designated group, most commonly a population.

Question 4

What is geneotype frequency?

Answer 4

The frequency or proportion of genotypes in a population. Gives an indication of the genotypes that are more or less prevalent in the population.

Question 5

Define heterozygosity.

Answer 5

The proportion of a population that has a heterozygous genotype.

Question 6

If an allele for a particular gene has a frequency of 1 in a population, how many different alleles does a population have at that locus?

Answer 6

If the frequency of the allele is 1, then all individuals in the population have the same allele for that gene. In other words, there is one type of allele at that locus. The population would therefore be homozygous and there is no genetic variation at that locus.

Question 7

What is the Hardy-Weinberg equilibrium?

Answer 7

A predictable ratio of genotype frequencies in a sexually reproducing population of infinite size with random mating and no selection, genetic drift or other evolutionary forces acting on it. It is represented in a one-locus, two-allele system as

p2 + 2pq + q2 = 1.

Question 8

Explain the Hardy-Weinberg principle

Answer 8

According to this principle, allele and genotype frequencies (i.e. genetic variation) in a population will remain constant from generation to generation provided that individuals in the population mate at random and there are no evolutionary mechanisms acting on that population.

Question 9

What is the Hardy-Weinberg equation?

Answer 9

A mathematical equation that describes the genotype frequencies expected at a locus under ideal equilibrium conditions in a random mating population:

p2 + 2pq + q2 = 1.

Question 10

What are the assumptions of the Hardy-Weinberg principle?

Answer 10

That mating is random; the population is infinitely large, or so large that it acts in effect as though it were infinite; that there is no natural selection; that there is no migration; that there is no mutation.

Question 11

Explain genetic drift

Answer 11

A change in the frequency of alleles or genotypes within a population due to the random sampling of organisms & not as a result of natural selection.

Question 12

Under what circumstances would the behaviour of the male redback spider (allowing his mate to eat him) be favoured by natural selection?

Answer 12

It would be favoured if the relative reproductive success of a male spider that allowed the female to eat him was higher than that of males which failed to behave in this way, given the behaviour was heritable.

Question 13

What is population genetics?

Answer 13

The study of distributions and changes in allele frequency in populations and genetic variation within and among species.

Question 14

Recall the definition of species according to the biological species concept (BSC).

Answer 14

According to the BSC, species are actually or potentially interbreeding populations that are reproductively isolated from other such groups.

Question 15

Define allele frequency

Answer 15

The frequency or proportion of each allele at a given locus within a designated group, most commonly a population.

Question 16

What is geneotype frequency?

Answer 16

The frequency or proportion of genotypes in a population. Gives an indication of the genotypes that are more or less prevalent in the population.

Question 17

Define heterozygosity.

Answer 17

The proportion of a population that has a heterozygous genotype.

Question 18

If an allele for a particular gene has a frequency of 1 in a population, how many different alleles does a population have at that locus?

Answer 18

If the frequency of the allele is 1, then all individuals in the population have the same allele for that gene. In other words, there is one type of allele at that locus. The population would therefore be homozygous and there is no genetic variation at that locus.

Question 19

What is the Hardy-Weinberg equilibrium?

Answer 19

A predictable ratio of genotype frequencies in a sexually reproducing population of infinite size with random mating and no selection, genetic drift or other evolutionary forces acting on it. It is represented in a one-locus, two-allele system as

p2 + 2pq + q2 = 1.

Question 20

Explain the Hardy-Weinberg principle

Answer 20

According to this principle, allele and genotype frequencies (i.e. genetic variation) in a population will remain constant from generation to generation provided that individuals in the population mate at random and there are no evolutionary mechanisms acting on that population.

Question 21

What is the Hardy-Weinberg equation?

Answer 21

A mathematical equation that describes the genotype frequencies expected at a locus under ideal equilibrium conditions in a random mating population:

p2 + 2pq + q2 = 1.

Question 22

What are the assumptions of the Hardy-Weinberg principle?

Answer 22

That mating is random; the population is infinitely large, or so large that it acts in effect as though it were infinite; that there is no natural selection; that there is no migration; that there is no mutation.

Question 23

Explain genetic drift

Answer 23

A change in the frequency of alleles or genotypes within a population due to the random sampling of organisms & not as a result of natural selection.

Question 24

Under what circumstances would the behaviour of the male redback spider (allowing his mate to eat him) be favoured by natural selection?

Answer 24

It would be favoured if the relative reproductive success of a male spider that allowed the female to eat him was higher than that of males which failed to behave in this way, given the behaviour was heritable.

Question 25

What are the mechanisms of evolutionary change?

Answer 25

Mechanisms of evolutionary change include natural selection, genetic drift, mutation and migration (or gene flow). All these can result in a change in allele frequencies in populations.

Question 26

Define deterministic

Answer 26

Describes a model or system in which there is no randomness - for any given starting condition, the outcome is always the same.

Question 27

What is the main cause of genetic drift?

Answer 27

random sampling of gametes at reproduction. Its effect on populations is much more profound in small populations than in large ones (which is why Hardy–Weinberg equilibrium requires populations to be infinitely large – to ensure that genetic drift is not operating).

Question 28

What is the difference between census population size and effective population size?

Answer 28

Census population size is the total number of individuals but effective population size is the number of individuals in a population that contribute offspring to the next generation.

Question 29

How might some genetic diversity be restored to populations emerging from a population bottleneck?

Answer 29

Through mutation and through gene flow (migration) from neighbouring populations.

Question 30

Explain the founder effect

Answer 30

A situation where a small number of founding individuals carry a fraction of the alleles present in the larger population, which results in reduced genetic variation.