BLOCK 4 - genetics

What is allele frequency?

Proportion of a specific allele in a population.

What is genotype frequency?

Number of individuals with a genotype ÷ total individuals.

How many alleles are in a diploid population?

2 × number of individuals.

How do you calculate allele frequency (p)?

p = (2×AA + Aa) ÷ total alleles.

How do you calculate q?

q = 1 − p.

Why is the distinction between genotype frequency and allele frequency important?

Genotype frequency ≠ allele frequency.

If 100 individuals, how many alleles are there?

200 alleles.

If p = 0.6, what is q?

0.4.

What is Hardy-Weinberg Equilibrium (HWE)?

A model where allele frequencies do not change.

What does HWE represent?

No evolution (null model).

What is the allele equation in HWE?

p + q = 1.

What is the genotype equation in HWE?

p² + 2pq + q² = 1.

What does p² represent?

Homozygous dominant.

What does 2pq represent?

Heterozygotes (carriers).

What does q² represent?

Homozygous recessive.

Why is a large population important in HWE?

Prevents genetic drift.

Why is random mating important in HWE?

Maintains genotype proportions.

Why is no mutation important in HWE?

No new alleles introduced.

Why is no selection important in HWE?

Equal survival.

Why is no migration important in HWE?

No gene flow.

Why should allele frequencies be equal in sexes in HWE?

Prevents bias.

What does it mean if HWE is violated?

Evolution is occurring.

What can HWE predict?

Genotype frequencies from allele frequencies.

What can HWE detect?

Evolutionary forces.

What is carrier frequency?

2pq.

Why are recessive alleles common?

Hidden in heterozygotes.

If disease frequency q² = 1/2000, what is q?

√(1/2000).

What gives carrier frequency?

2pq.

Why is HWE different for X-linked genes?

Males have one X (hemizygous).

What is male genotype frequency equal to?

Allele frequency.

Why are X-linked recessive diseases more common in males?

Only one allele needed.

What is non-random mating?

Individuals choose mates based on genotype.

Does non-random mating change allele frequency?

No.

What does non-random mating change?

Genotype proportions.

What is population structure?

Subgroups with different allele frequencies.

What is the Wahlund effect?

Reduced heterozygosity when populations mix.

Why does the Wahlund effect occur?

Different allele frequencies in subpopulations.

What is FST?

Measure of genetic difference between populations.

What does FST = 0 mean?

Populations identical.

What does FST = 1 mean?

Populations completely different.

What does high FST indicate?

Strong differentiation.

What does low FST indicate?

Populations are similar.

What is genetic drift?

Random change in allele frequency.

When is genetic drift strongest?

Small populations.

What does genetic drift cause?

Loss or fixation of alleles.

What happens to heterozygosity due to genetic drift?

Decreases.

What is a bottleneck?

Population size drastically reduced.

What is the founder effect?

Small group forms new population.

What is the consequence of both bottleneck and founder effect?

Reduced genetic diversity.

What is Ne?

Size of ideal population losing diversity at same rate.

Is Ne equal to actual population size?

No (Ne < N).

Why is Ne smaller than actual population size?

Unequal sex ratio, reproduction differences, population changes.

What happens when Ne is small?

Stronger genetic drift.

What does HWE imply?

No evolution.

What happens when assumptions of HWE are broken?

Evolution occurs.

When is drift strongest?

When Ne is small.

What does the Wahlund effect indicate?

Decreased heterozygotes.

What does FST measure?

Population differences.