Lesch-Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that pr

Question

Lesch-Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.

Part A
What is the probability that the first son of a woman whose brother has Lesch-Nyhan syndrome will be affected?
Express your answer as a fraction (example 1/16).

Part B:
If the first son of the woman described in (a) is affected, what is the probability that her second son is affected?
Express your answer as a fraction (example 1/16).

Part C
What is the probability that the first son of a man whose brother has Lesch-Nyhan syndrome will be affected?
Express your answer using one decimal place.

Explanation / Answer

A.

Since the woman’s brother is affected, her mother must be a carrier for the recessive allele. Therefore, the probability that she is a carrier is ½ or 0.5. The probability that she passes the recessive allele is ½ or 0.5. Therefore, the probability that the womans first son will be affected is ½ × ½ = 1/4.

B.

The first offspring being affected shows that the woman is a carrier of the recessive allele. Therefore, the probability that her second child is affected is 1/ 2 or 0.5.

C.

The man is not affected. Since Lesch-Nyhan syndrome is X-linked, the man does not pass X-chromosome to his offspring. Therefore, the probability is 0. The chances of inheriting the syndrome for men counts only if the mother is a carrier or affected.

Related Questions

Navigate

• Browse (All)
• Browse L
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.