ABMGG Inheritance Patterns and Population Genetics Flashcards
6 cards from real ABMGG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
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A de novo pathogenic variant in a gene causes severe disease in a proband whose parents are unaffected. What is the approximate recurrence risk for future siblings?
Answer: 1–2% due to possible germline mosaicism in a parent
Even when neither parent shows the variant by blood testing, low-level germline mosaicism in a parent can raise sibling recurrence risk to ~1–2%.
Somatic mosaicism for a gain-of-function pathogenic variant in a parent can lead to which outcome in their offspring?
Answer: A child with full germline heterozygosity and more severe disease than the mosaic parent
If the variant is in the parent's germline cells, it can be transmitted as a fully heterozygous allele to the child, who then expresses the full phenotype.
Which concept explains why two siblings with the same pathogenic CFTR genotype can have markedly different disease severity?
Answer: Variable expressivity
Variable expressivity refers to the range of signs and symptoms that can occur in individuals with the same pathogenic genotype, influenced by modifier genes and environment.
Founder effects in isolated populations increase the prevalence of specific genetic diseases because:
Answer: A small founding population may carry a pathogenic allele at high frequency due to genetic drift
If a founding individual carried a rare pathogenic allele, it can reach unexpectedly high frequency in descendants due to drift and small effective population size.
In X-linked dominant inheritance, which statement best describes the pattern of affected individuals?
Answer: Both males and females are affected, but males typically have more severe disease
In X-linked dominant conditions, hemizygous males often have more severe disease (sometimes lethal in utero) while heterozygous females are affected but typically less severely.
What does the coefficient of relationship (r) quantify in genetic counseling for consanguineous couples?
Answer: The proportion of genes shared identical by descent between two related individuals
The coefficient of relationship r = 2F, where F is the inbreeding coefficient; for first cousins r = 0.125, meaning they share ~12.5% of their genome by descent.