CGC Population Genetics & Epidemiology 2 — Questions and Answers
Question 1: Penetrance in genetics refers to:
- The severity of disease in affected individuals
- The proportion of individuals with a given genotype who exhibit the associated phenotype (Correct answer)
- The age at which a genetic condition first appears
- The number of genes responsible for a condition
Correct answer: The proportion of individuals with a given genotype who exhibit the associated phenotype
Penetrance is the proportion of individuals with a pathogenic genotype who show clinical features; incomplete penetrance means not all carriers are affected.
Question 2: Variable expressivity in genetics means:
- A gene is expressed in some tissues but not others
- Individuals with the same pathogenic variant may show different degrees or types of clinical features (Correct answer)
- The gene is only expressed in males
- Some pathogenic variants are more severe than others in the same individual
Correct answer: Individuals with the same pathogenic variant may show different degrees or types of clinical features
Variable expressivity describes the range in clinical severity or phenotypic features seen among individuals who share the same pathogenic variant.
Question 3: Which measure of disease frequency represents the proportion of a population affected with a condition at a specific point in time?
- Incidence
- Point prevalence (Correct answer)
- Cumulative incidence
- Attributable risk
Correct answer: Point prevalence
Point prevalence measures the proportion of individuals in a population who have a condition at a specific moment in time.
Question 4: Locus heterogeneity refers to the situation where:
- Multiple alleles at the same locus cause the same disease
- Mutations at different gene loci can all cause the same clinical phenotype (Correct answer)
- One gene causes multiple different phenotypes
- A condition shows both dominant and recessive inheritance
Correct answer: Mutations at different gene loci can all cause the same clinical phenotype
Locus heterogeneity means clinically similar conditions can result from variants in different genes, complicating genetic testing interpretation.
Question 5: Allelic heterogeneity refers to:
- Different genes causing the same phenotype
- Multiple different variants within the same gene causing the same or related phenotypes (Correct answer)
- A single variant causing multiple different diseases
- Heterozygous variants at the same locus
Correct answer: Multiple different variants within the same gene causing the same or related phenotypes
Allelic heterogeneity describes the existence of multiple distinct pathogenic variants within the same gene that all produce the same or similar phenotype.
Question 6: A genetic counselor explains that a condition has a population prevalence of 1 in 10,000. Using Hardy-Weinberg, the carrier frequency is approximately:
- 1 in 100
- 1 in 50 (Correct answer)
- 1 in 200
- 1 in 10,000
Correct answer: 1 in 50
For q² = 1/10,000, q = 1/100; carrier frequency 2pq ≈ 2q = 1/50, since p ≈ 1 for rare recessive conditions.
CGC Population Genetics & Epidemiology 2
Penetrance in genetics refers to: