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MCQ Practice

Biology MCQs

Huntington’s disease, characterized by neurodegeneration and anticipation, is inherited in which manner?

  • A. Autosomal recessive
  • B. Autosomal dominant
  • C. X-linked recessive
  • D. Mitochondrial
Explanation:
Huntington’s disease is autosomal dominant (one mutant allele is sufficient) and shows anticipation due to CAG repeat expansion, but inheritance is strictly dominant.

A point mutation changes a codon for an amino acid to a stop codon. This is called a:

  • A. Missense mutation
  • B. Silent mutation
  • C. Nonsense mutation
  • D. Frameshift mutation
Explanation:
Changing an amino acid codon to a stop codon prematurely terminates translation, producing a truncated protein; this is a nonsense mutation.

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
Explanation:
A sex-influenced trait has different phenotypic dominance in males vs females (due to hormonal differences), as seen with baldness alleles.

One gene’s product is epistatic to another gene’s product, meaning:

  • A. Both genes contribute equally to a single trait
  • B. One gene’s effect masks or hides the effect of another
  • C. The two genes are linked on the same chromosome
  • D. The genes show incomplete dominance
Explanation:
Epistasis occurs when the expression of one gene masks the effect of another gene (e.g., a loss-of-function in one gene may prevent the other gene from having an effect).

A single gene mutation causes both phenylketonuria (affecting skin pigment) and neurological impairment. This phenomenon is called:

  • A. Epistasis
  • B. Pleiotropy
  • C. Codominance
  • D. Penetrance
Explanation:
One gene affecting multiple, seemingly unrelated traits (e.g., PKU’s effects on pigment and brain) is pleiotropy.

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
Explanation:
Height is a quantitative trait determined by multiple genes (polygenes) and the environment, consistent with polygenic inheritance.

Two genes exhibit a recombination frequency of 20% in genetic crosses. Which statement is most accurate?

  • A. The genes are likely on different chromosomes
  • B. The genes are roughly 20 map units apart on the same chromosome
  • C. The genes are so far apart that they assort independently
  • D. The genes are allelic variants of each other
Explanation:
A recombination frequency of 20% indicates that the genes are linked (~20 centimorgans apart) on the same chromosome and not assorting completely independently.

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%
Explanation:
A cross Aa (carrier) × aa (normal) yields 50% Aa (carriers) and 50% aa (unaffected, non-carriers).

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
Explanation:
Autosomal recessive traits can skip generations. Two carriers (phenotypically normal) can produce an affected child (25% chance).

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
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.