ABMGG ABMGG Inheritance Patterns and Population Genetics 1 — Questions and Answers
Question 1: In autosomal dominant inheritance, what is the recurrence risk for each offspring of an affected parent?
- 50% (Correct answer)
- 25%
- 100%
- 0%
Correct answer: 50%
An affected parent carries one pathogenic allele on one of the two autosomes; each child has a 50% chance of inheriting that allele.
Question 2: Which inheritance pattern is characterized by transmission exclusively through the maternal line with variable expressivity among family members?
- Mitochondrial inheritance (Correct answer)
- X-linked recessive inheritance
- Autosomal dominant with reduced penetrance
- Y-linked inheritance
Correct answer: Mitochondrial inheritance
Mitochondrial DNA is maternally inherited; all children of an affected mother may be affected but paternal transmission never occurs.
Question 3: A couple is each a carrier of the same autosomal recessive variant. What is the probability that their child will be an unaffected carrier?
- 50% (Correct answer)
- 25%
- 75%
- 0%
Correct answer: 50%
In a carrier × carrier cross, the expected genotypic ratio is 1 homozygous normal : 2 carriers : 1 affected, so carriers make up 2/4 = 50% of offspring.
Question 4: Genomic imprinting results in disease when:
- Both copies of a gene are inherited from the same parent (uniparental disomy) or one copy's imprint is erased (Correct answer)
- A dominant allele fails to be expressed due to low penetrance
- A recessive variant occurs in compound heterozygous form
- Trinucleotide repeats expand during maternal transmission only
Correct answer: Both copies of a gene are inherited from the same parent (uniparental disomy) or one copy's imprint is erased
Imprinted genes are expressed from only one parental allele; uniparental disomy or imprinting center defects silence both working copies, causing disease.
Question 5: What term describes the phenomenon where carrier females of an X-linked recessive condition are clinically affected due to skewed X-inactivation?
- Manifesting carrier (Correct answer)
- Obligate carrier
- Hemizygous affected
- Compound heterozygote
Correct answer: Manifesting carrier
When the normal X chromosome is preferentially inactivated in most cells, the carrier female expresses the disease to varying degrees and is called a manifesting carrier.
Question 6: Hardy-Weinberg equilibrium predicts allele frequencies in a population remain stable under which set of conditions?
- Random mating, no mutation, no selection, no genetic drift, no gene flow (Correct answer)
- Inbreeding, large population size, selective pressure, high mutation rate
- Random mating, small population, founder effect, no migration
- Non-random mating, no selection, equal sex ratio, high recombination
Correct answer: Random mating, no mutation, no selection, no genetic drift, no gene flow
Hardy-Weinberg equilibrium holds only when five conditions are met: random mating, no mutation, no natural selection, infinite population size, and no migration.
ABMGG ABMGG Inheritance Patterns and Population Genetics 1
In autosomal dominant inheritance, what is the recurrence risk for each offspring of an affected parent?