ABMGG ABMGG Inheritance Patterns and Population Genetics 2

Question 1

Locus heterogeneity in genetic disease means that:

Accepted Answer

Mutations in different genes can cause the same clinical phenotype

Answer

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

Question 2

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

Accepted Answer

Expansion of unstable trinucleotide repeats with each generation

Answer

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

Question 3

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

Accepted Answer

Penetrance

Answer

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

Question 4

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

Accepted Answer

Homozygosity for the same pathogenic allele inherited from a common ancestor

Answer

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.

Question 5

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

Accepted Answer

1 in 25

Answer

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).

ABMGG - American Board of Medical Genetics and Genomics Practice Test

ABMGG - American Board of Medical Genetics and Genomics Practice Test

ABMGG ABMGG Inheritance Patterns and Population Genetics 2