Population Genetics (LEC)

What is the principle of allele segregation in populations at Hardy-Weinberg Equilibrium?

Alleles segregate as either p (homozygous dominant) or q (homozygous recessive), with the relationship p + q = 1.

How are allele frequencies represented in Hardy-Weinberg Equilibrium?

Allele frequencies are represented as p, for the dominant allele, and q, for the recessive allele.

What is the equation relating allele frequency to genotype frequency in a population?

The genotype frequency can be calculated using the equation p² + 2pq + q² = 1.

What do p², 2pq, and q² represent in terms of genotype frequency?

p² represents the frequency of homozygous dominant individuals, 2pq represents the frequency of heterozygous individuals, and q² represents the frequency of homozygous recessive individuals.

How to calculate the frequency of the disease-causing allele (q) in autosomal recessive disorders?

The frequency of the disease-causing allele (q) is derived from the incidence (I) of the disease in the population, where q = I.

What is the relationship between the frequency of the disease-causing allele (q) and the frequency of the normal allele (p)?

The relationship is given by p = 1 - q.

If the incidence rate of an autosomal recessive disorder is 1/10,000, what is the frequency of the disease-causing allele (q)?

q = 1/10,000 = 0.0001.

How to calculate the frequency of homozygous dominant (unaffected) and homozygous recessive (affected) individuals in a population?

For a recessive allele frequency q, the homozygous dominant frequency is p² = (1 - q)² and the homozygous recessive frequency is q².

Calculate the carrier frequency for a population with an AR disorder where q = 0.01.

The carrier frequency (heterozygous) can be calculated using 2pq = 2(1 - q)(q) = 2(0.99)(0.01) = 0.0198.

How does the total frequency of genotypes relate to the Hardy-Weinberg principle?

The sum of the frequencies of all genotypes (homozygous dominant, heterozygous, and homozygous recessive) in a Hardy-Weinberg population adds up to 1: p² + 2pq + q² = 1.

How is allele frequency estimated for autosomal dominant disorders when homozygosity is rare?

In autosomal dominant disorders, the allele frequency can be estimated using the formula 2pq = (I) - 1, where p is approximately 1 and q is the frequency of the disease allele.

If an autosomal dominant disorder (e.g., retinoblastoma) has an incidence rate of 1/25,000, how can you calculate q?

Using the equation 2(1)q = (1/25,000) - 1, we find that q = 1/50,000, meaning about 1 in 50,000 people carries the disease-causing allele.

What is the significance of heterozygosity and homozygosity in autosomal dominant conditions?

Homozygosity for autosomal dominant alleles is very rare; typically, the phenotype of the homozygote is more severe than that of the heterozygote.

What is the significance of male hemizygosity for X-linked genes in relation to Hardy-Weinberg equilibrium?

Males are hemizygous for X-linked genes, which simplifies the Hardy-Weinberg equation to p + q = 1; men with the q allele are affected, while those with the p allele are not affected.

How is the incidence of X-linked disorders represented in males?

In males, the incidence of X-linked disorders corresponds to the frequency of the disease-causing allele (q), such that q = I (incidence).

How can the proportion of female carriers for X-linked disorders be estimated?

The proportion of female carriers can be obtained from the equation 2pq, where p represents the frequency of the normal allele and q the frequency of the disease-causing allele.

If an X-linked disorder (e.g., choroideremia) has an incidence rate of 1/25,000, what is the value of q for males?

q = 1/25,000 for males corresponding to the incidence of the disorder.

How do you calculate the carrier rate for female carriers of an X-linked disorder?

The carrier rate for females can be calculated as 2pq; for instance, with q = 1/25,000 and assuming p ≈ 1, it results in a carrier rate of 2(1)(1/25,000) = 1/12,500.

Why are rare autosomal dominant alleles expected to be infrequent?

Rare autosomal dominant alleles are infrequent because individuals who are homozygous dominant for the allele often exhibit low reproductive fitness, preventing them from passing on the trait to future generations.

What is the reproductive advantage of heterozygous individuals with autosomal dominant disorders?

Heterozygous individuals for autosomal dominant disorders typically have better reproductive fitness compared to homozygous dominant individuals, allowing them to pass the allele to the next generation.

How does the Hardy-Weinberg equation relate to the frequency of rare autosomal dominant alleles?

Using the Hardy-Weinberg equation, the frequency of the rare allele (q) remains low due to the rarity of homozygous dominant individuals and the limited reproductive success associated with