ABMGG Inheritance Patterns and Population Genetics Flashcards

Locus heterogeneity in genetic disease means that:

Answer: Mutations in different genes can cause the same clinical phenotype

Locus heterogeneity describes when mutations at distinct chromosomal loci produce an indistinguishable phenotype, as seen in retinitis pigmentosa with >70 causative genes.

What is the genetic basis of anticipation, seen in conditions such as myotonic dystrophy?

Answer: Expansion of unstable trinucleotide repeats with each generation

Unstable repeat tracts tend to expand during meiosis; larger repeat sizes correlate with earlier onset and more severe disease in successive generations.

Which parameter describes the proportion of individuals with a pathogenic genotype who manifest clinical features of the associated disease?

Answer: Penetrance

Penetrance is defined as the proportion of individuals with the causative genotype who show any sign of the associated phenotype.

In autosomal recessive disease, consanguinity increases disease risk primarily because it increases the probability of:

Answer: Homozygosity for the same pathogenic allele inherited from a common ancestor

Related parents share segments of their genome identical by descent; when both carry the same recessive allele, offspring have a higher chance of inheriting two copies.

The population carrier frequency for cystic fibrosis in individuals of Northern European ancestry in the US is approximately:

Answer: 1 in 25

CF carrier frequency is ~1/25 in Northern Europeans, giving a disease incidence of ~1/2,500 (the product of 1/25 × 1/25 × 1/4 for two carriers).

What inheritance pattern is most consistent with a pedigree showing only males affected across multiple generations, with transmission exclusively through daughters who are unaffected?

Answer: X-linked recessive

In X-linked recessive disease, carrier females pass the mutant X to 50% of sons (affected) and 50% of daughters (carriers), with no male-to-male transmission.