Sex-linked traits and reading pedigrees — NEET & JEE Questions

Question 1 · difficulty L1 · recall

A classic X-linked recessive human disorder:

• A. Down syndrome
• B. Turner syndrome
• C. haemophilia
• D. Klinefelter syndrome

Question 2 · difficulty L2 · understanding

Why are X-linked recessive traits expressed more often in human males than in females?

• A. Males inherit two X chromosomes
• B. Males have only one X chromosome
• C. The Y chromosome carries a matching dominant allele
• D. Females never inherit recessive alleles

Question 3 · difficulty L2 · understanding

An X-linked recessive trait is more commonly expressed in human males because males

• A. have only one X chromosome
• B. have two X chromosomes
• C. lack autosomes
• D. inherit no genes from their mothers

Question 4 · difficulty L2 · understanding

In a pedigree, a carrier female for an X-linked recessive trait is usually

• A. phenotypically unaffected but heterozygous
• B. affected and homozygous recessive
• C. male and hemizygous
• D. unable to transmit the allele

Question 5 · difficulty L3 · application

A carrier mother for an X-linked recessive disorder and an unaffected father have a son. What is the probability that the son is affected?

• A. 1/2
• B. 1/4
• C. 3/4
• D. 1

Question 6 · difficulty L3 · application

An affected man with an X-linked recessive trait mates with a non-carrier unaffected woman. Which statement is correct?

• A. All daughters receive his affected X and are carriers
• B. All sons are affected
• C. Half the sons are carriers
• D. No daughter receives his X chromosome

Question 7 · difficulty L3 · application

In a pedigree, affected males are connected through unaffected carrier females, and there is no father-to-son transmission. This pattern suggests

• A. X-linked recessive inheritance
• B. Y-linked inheritance
• C. autosomal dominant inheritance only
• D. mitochondrial inheritance only

Question 8 · difficulty L3 · application

A woman has an affected father for an X-linked recessive disorder and an unaffected non-carrier mother. The woman is expected to be

• A. an obligate carrier
• B. affected
• C. unable to inherit the allele
• D. homozygous normal

Question 9 · difficulty L4 · analysis

A pedigree shows an affected father and an unaffected mother. All daughters are carriers, while no sons are affected. Which inheritance pattern best fits?

• A. Mitochondrial inheritance
• B. Autosomal dominant inheritance
• C. Y-linked inheritance
• D. X-linked recessive inheritance

Question 10 · difficulty L4 · application

A carrier female $X^AX^a$ mates with an affected male $X^aY$. What fraction of all children is expected to be affected, assuming equal sex probability?

• A. 1/2
• B. 1/4
• C. 3/4
• D. 1