In the analysis of a family, you notice that males are more likely to contract a certain disease and the daughters of affected males produce 50% of their sons affected with the disease. This disease is displaying what pattern of inheritance?单项选择题
A
X-linked recessive
B
Autosomal recessive
C
Autosomal dominant
D
X-linked dominant

Question

In the analysis of a family, you notice that males are more likely to contract a certain disease and the daughters of affected males produce 50% of their sons affected with the disease. This disease is displaying what pattern of inheritance?单项选择题

A

X-linked recessive

B

Autosomal recessive

C

Autosomal dominant

D

X-linked dominant

BlackTom AI · Accepted Answer

X-linked recessive inheritance explains the pattern because males are hemizygous for X-linked alleles and therefore express recessive mutations more often.

1) Relevant knowledge points and concepts
- Males have XY, females XX. A recessive allele on the X chromosome (Xr) is expressed in males if present because they have no second X to mask it. Females must have two copies (Xr/Xr) to be affected; heterozygous females (XRXr) are usually carriers. An affected male transmits his single X to all daughters (making them carriers if the mother provides a normal X) and transmits his Y to all sons.

2) Step-by-step reasoning
- Start with an affected male genotype XrY and an unaffected, noncarrier female XRXR.
- Their children: daughters receive Xr from father and XR from mother → XRXr (carriers); sons receive Y from father and XR from mother → XRY (unaffected).
- Those carrier daughters (XRXr), when they have children with an unaffected male (XRY), have a 50% chance of passing Xr to each child.
- Sons of a carrier daughter have a 50% chance of being XrY (affected) because sons inherit the X chromosome from their mother and Y from their father.

3) Intermediate steps / Punnett outcomes shown
- Affected father × noncarrier mother: daughters = 100% carriers (XRXr); sons = 0% affected (XRY).
- Carrier daughter (XRXr) × unaffected father (XRY): children probabilities:
  - Daughters: 50% XRXR (unaffected), 50% XRXr (carrier).
  - Sons: 50% XRY (unaffected), 50% XrY (affected).
- Thus daughters of affected males produce 50% affected sons — matches the observation.

4) Why the correct answer is correct
- The described pattern (males more commonly affected, daughters of affected males producing ~50% affected sons) is the classic signature of X-linked recessive inheritance because of hemizygosity in males and carrier transmission through daughters.

5) Why the other options are incorrect
- Autosomal recessive: would affect males and females equally and require two mutant alleles in affected individuals; it wouldn’t produce the sex-biased pattern described.
- Autosomal dominant: would also affect both sexes equally and typically shows vertical transmission (affected parent to ~50% of children of either sex).
- X-linked dominant: affected males transmit the trait to all daughters and no sons, and females are often affected too; daughters of affected males would be affected themselves, not merely carriers who transmit to ~50% of sons.

6) Conclusion
This pattern is X-linked recessive, which matches the provided answer: X-linked recessive.

In the analysis of a family, you notice that males are more likely to contract a certain disease and the daughters of affected males produce 50% of their sons affected with the disease. This disease is displaying what pattern of inheritance?单项选择题

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