Question

1. a mother wants to know whether her unborn son might contract a recessive trait that she carries. which of the following circumstances would result in her son showing the recessive trait?

the baby inherits a dominant allele from the mother only.
the baby inherits a recessive allele from the father only.
the baby inherits a recessive allele from both the father and the mother.
the baby inherits a dominant allele from both the father and the mother.

Explanation:

To express a recessive trait, an individual must have two recessive alleles (homozygous recessive). The mother is a carrier (so she has one recessive allele). For the son to show the recessive trait, he needs to inherit a recessive allele from the mother (who is a carrier) and also a recessive allele from the father. Let's analyze each option:

• Option 1: Inheriting a dominant allele from both parents would result in the dominant trait being expressed, not the recessive trait.
• Option 2: If the baby inherits a recessive allele from both the father and the mother, then the baby has two recessive alleles (homozygous recessive) and will show the recessive trait. Since the mother is a carrier (has one recessive allele), if the father also contributes a recessive allele, this situation can occur and the son will show the recessive trait.
• Option 3: Inheriting a recessive allele from the father only, while the mother is a carrier (has one recessive allele, but if the mother passes a dominant allele, then the son would have one dominant and one recessive allele, and the dominant trait would be expressed, not the recessive trait).
• Option 4: Inheriting a dominant allele from the mother only, and we don't know about the father's allele, but just one dominant allele (if the father also gives a dominant allele, dominant trait is expressed; if father gives recessive, then one dominant and one recessive, dominant trait is expressed). So this does not guarantee the recessive trait is shown.

Answer:

The baby inherits a recessive allele from both the father and the mother. (The second option in the list of choices, assuming the options are ordered as: 1. The baby inherits a dominant allele from both the father and the mother. 2. The baby inherits a recessive allele from both the father and the mother. 3. The baby inherits a recessive allele from the father only. 4. The baby inherits a dominant allele from the mother only.)