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Chapter 4: Problem 15

A human disease known as vitamin D-resistant rickets is inherited as an X-linked dominant trait. If a male with the disease produces children with a female who does not have the disease, what is the expected ratio of affected and unaffected offspring?

Short Answer

Expert verified
The expected ratio of affected to unaffected children is 1:1, with all daughters being affected and all sons being unaffected.

Step by step solution

01

Understanding X-linked dominant traits

An X-linked dominant trait means that having only one copy of the mutant gene on the X chromosome leads to the expression of the trait. In a male (who is XY), this means that if they have the trait, their only X chromosome carries the gene, thus they would pass it on to all of their daughters but none of their sons (since males pass their Y chromosome, not the X, to their sons).
02

Understanding the mating and offspring characteristics

In the given question, a male with the disease (meaning his X chromosome carries this disease gene) has children with a female who does not have the disease (meaning both of her X chromosomes are unaffected). Now, considering each offspring, daughters will receive one X chromosome from their father (carrying the disease trait) and one from their mother (not carrying the trait). Thus, all daughters will inherit the disease because it is a dominant trait and it only requires one copy of the gene to be present. Sons, on the other hand, will receive an X chromosome from their mother (without the trait) and a Y chromosome from their father (which does not carry the trait), meaning all sons will be unaffected.
03

Calculating Expected Ratio

If the cross is between a female with genotype XX (where both X chromosomes are normal) and a male with genotype XdY (where Xd denotes the X chromosome with the dominant disease gene and Y the normal Y chromosome), all female offspring (XXd) will have the disease, while all male offspring (XY) will not. Therefore, the expected ratio of affected to unaffected offspring is 1:1, considering only the sex of the offspring. Specifically, all daughters will be affected and all sons will be unaffected.

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Most popular questions from this chapter

In Shorthorn cattle, coat color is controlled by a single gene that can exist as a red allele \((R)\) or a white allele \((r)\). The heterozygotes \((R r)\) have a color called roan that looks less red than the \(R R\) homozygotes. However, when examined carefully, the roan phenotype in cattle is actually due to a mixture of completely red hairs and completely white hairs. Should this be called incomplete dominance, codominance, or something else? Explain your reasoning.

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Hemophilia is an X-linked recessive trait in humans. If a heterozygous woman has children with an unaffected man, what is the probability of each of the following combinations of children? A. An affected son B. Four unaffected offspring in a row C. An unaffected daughter or son D. Two affected offspring out of five

Discuss the differences among sex-influenced, sex-limited, and sex-linked inheritance. Give examples.
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