Selected MCQ

Current Question
Which inheritance pattern is suggested if every affected father passes the trait to all his daughters but to none of his sons?
  • A. X-linked recessive
  • B. X-linked dominant
  • C. Autosomal recessive
  • D. Mitochondrial inheritance
Correct Answer: B
Explanation:
An affected male (XY) passing a trait to all daughters (who get his X) and no sons is characteristic of X-linked dominant inheritance.
Related Question 1
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 2
In a pedigree, if two unaffected parents have an affected child, the trait is most likely:
  • A. Autosomal dominant
  • B. Autosomal recessive
  • C. X-linked dominant
  • D. X-linked recessive
Correct Answer: B
Explanation:
Autosomal recessive traits can skip generations. Two carriers (phenotypically normal) can produce an affected child (25% chance).
Related Question 3
A mother carries a mutated X-linked recessive gene but is unaffected. What is the probability that a son of hers will express the trait?
  • A. 0%
  • B. 25%
  • C. 50%
  • D. 100%
Correct Answer: C
Explanation:
A carrier mother (X^mX) has a 50% chance of passing the mutant X to a son. If he receives it, he will express the recessive trait (since sons inherit only one X chromosome).
Related Question 4
Which of the following best describes polygenic inheritance?
  • A. One gene affects multiple traits (e.g., pleiotropy)
  • B. Many genes contribute to one trait (e.g., skin color)
  • C. A trait determined by genes only on the X chromosome
  • D. Inheritance of mitochondrial DNA
Correct Answer: B
Explanation:
Polygenic inheritance means multiple genes (often with additive effects) determine a single phenotype, such as height or skin color, producing continuous variation.
Related Question 5
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.