CGC Molecular Genetics & Mechanisms of Inheritance 3

Question 1

Heteroplasmy in mitochondrial genetics refers to:

Accepted Answer

A mixture of two or more mitochondrial DNA genotypes within a cell or individual

Answer

Heteroplasmy describes the coexistence of wild-type and mutant mitochondrial DNA within the same cell or tissue; the proportion of mutant mtDNA (mutation load) influences clinical severity.

Question 2

Germline mosaicism occurs when a mutation is present in some but not all of a parent's germline cells. What is the primary clinical implication for genetic counseling?

Accepted Answer

The recurrence risk for future pregnancies is higher than the population risk but lower than 50%, making standard dominant inheritance risk estimates inaccurate

Answer

Germline mosaicism can produce multiple affected children from apparently unaffected parents; recurrence risk is greater than de novo rates but typically less than 50%, complicating risk counseling.

Question 3

Which term describes the situation where a single gene mutation causes multiple, seemingly unrelated phenotypic effects?

Accepted Answer

Pleiotropy

Answer

Pleiotropy refers to the phenomenon where a single gene mutation produces effects in multiple organ systems or tissues, as seen in Marfan syndrome (cardiac, skeletal, and ocular features from FBN1 mutations).

Question 4

Locus heterogeneity in genetics means that:

Accepted Answer

The same disease phenotype can result from mutations at different genetic loci

Answer

Locus heterogeneity occurs when the same clinical phenotype can be caused by mutations in different genes (e.g., retinitis pigmentosa is caused by mutations in over 60 different genes).

Question 5

The protein product of a dominant negative mutation typically:

Accepted Answer

Interferes with the function of the normal protein produced by the wild-type allele

Answer

Dominant negative mutations produce an abnormal protein that interferes with the normal protein (often in multimeric complexes), causing greater functional loss than simple haploinsufficiency would predict.

CGC - Certified Genetic Counselor Practice Test

CGC - Certified Genetic Counselor Practice Test

CGC Molecular Genetics & Mechanisms of Inheritance 3