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If a trait is sex-linked and recessive, what is the probability that a son will

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Question: If a trait is sex-linked and recessive, what is the probability that a son will express the trait if his mother is a carrier and his father does not have the trait?

Options:

  1. 0%
  2. 25%
  3. 50%
  4. 100%

Correct Answer: 50%

Solution: 

The son will inherit the X chromosome from his mother. If she is a carrier (X^HX^h), there is a 50% chance he will inherit the X^h and express the trait.

If a trait is sex-linked and recessive, what is the probability that a son will

Practice Questions

Q1
If a trait is sex-linked and recessive, what is the probability that a son will express the trait if his mother is a carrier and his father does not have the trait?
  1. 0%
  2. 25%
  3. 50%
  4. 100%

Questions & Step-by-Step Solutions

If a trait is sex-linked and recessive, what is the probability that a son will express the trait if his mother is a carrier and his father does not have the trait?
  • Step 1: Understand that the trait is sex-linked and recessive. This means it is carried on the X chromosome and will only show if a person has two copies of the recessive allele (X^h).
  • Step 2: Identify the mother's genotype. Since she is a carrier, her genotype is X^H X^h. This means she has one normal allele (X^H) and one recessive allele (X^h).
  • Step 3: Identify the father's genotype. Since he does not have the trait, his genotype is X^H Y. He has one normal X chromosome and one Y chromosome.
  • Step 4: Determine which X chromosome the son will inherit from his mother. Sons inherit their X chromosome from their mother and their Y chromosome from their father.
  • Step 5: Since the mother is X^H X^h, there are two possible X chromosomes she can pass to her son: X^H or X^h.
  • Step 6: Calculate the probability of the son inheriting the X^h chromosome. There are two options (X^H or X^h), so the chance of inheriting X^h is 1 out of 2, or 50%.
  • Step 7: Conclude that if the son inherits the X^h chromosome, he will express the trait because he has only one X chromosome.
  • Sex-linked inheritance – Traits that are associated with genes located on the sex chromosomes, particularly the X chromosome.
  • Recessive traits – Traits that require two copies of the allele (or one copy from the X chromosome in males) to be expressed.
  • Carrier status – An individual who has one copy of a recessive allele and does not express the trait but can pass it to offspring.
  • Inheritance patterns – Understanding how traits are passed from parents to offspring, particularly in the context of sex-linked traits.
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