Selected MCQ

Current Question
Male pattern baldness is dominant in men but recessive in women. This is an example of:
  • A. X-linked inheritance
  • B. Sex-influenced trait
  • C. Codominance
  • D. Autosomal dominance
Correct Answer: B
Explanation:
A sex-influenced trait has different phenotypic dominance in males vs females (due to hormonal differences), as seen with baldness alleles.
Related Question 1
A female exhibits an X-linked recessive trait. What must be true of her parents’ genotypes?
  • A. Her father must have the trait, and her mother must be at least a carrier
  • B. Both parents must be affected
  • C. Only her mother is affected
  • D. Either parent could have the trait independently
Correct Answer: A
Explanation:
For a daughter to be homozygous for an X-linked recessive allele, her father must have the allele (so he is affected) and her mother must carry at least one mutant X.
Related Question 2
Phenylketonuria (PKU) is inherited as an autosomal recessive trait. If two carriers have a child, what is the probability the child will be unaffected (no mutant alleles)?
  • A. 100%
  • B. 75%
  • C. 50%
  • D. 25%
Correct Answer: B
Explanation:
For two carriers (Aa × Aa), the offspring genotype ratio is 1 AA: 2 Aa: 1 aa. 75% (AA + Aa) are unaffected (though 50% are carriers).
Related Question 3
In genomic imprinting, the expression of a gene depends on its parental origin. For example, only the paternally inherited allele of a certain gene is expressed. This is known as:
  • A. Epigenetic modification
  • B. Loss of heterozygosity
  • C. Imprinting
  • D. Mendelian inheritance
Correct Answer: C
Explanation:
Genomic imprinting is an epigenetic phenomenon where only one allele (maternal or paternal) is expressed, depending on the parent of origin, while the other is silenced.
Related Question 4
Inheritance of human height, which is influenced by many genes and environmental factors, is an example of:
  • A. Codominance
  • B. Polygenic inheritance
  • C. Pleiotropy
  • D. Autosomal dominance
Correct Answer: B
Explanation:
Height is a quantitative trait determined by multiple genes (polygenes) and the environment, consistent with polygenic inheritance.
Related Question 5
If a couple consists of one carrier for an autosomal recessive allele and one homozygous normal, what fraction of their children will be carriers (heterozygotes)?
  • A. 0%
  • B. 25%
  • C. 50%
  • D. 100%
Correct Answer: C
Explanation:
A cross Aa (carrier) × aa (normal) yields 50% Aa (carriers) and 50% aa (unaffected, non-carriers).