Hemophilia is a sex-linked recessive disease. A mother who is a carrier of the disease makes a healthy male. Which of the following statements is true?
Correct answer: D. 50% of sons will have hemophilia
- A. The daughters are just as likely to be hemophilic as the sons are
- B. 50% of the daughters will have hemophilia
- C. None of the children will have hemophilia because the mother is the only carrier
- D. 50% of sons will have hemophilia
Explanation
In the given scenario where a mother is a carrier of the sex-linked recessive disease hemophilia and mates with a healthy man, the following statement is true: 50% of sons will have hemophilia. Hemophilia is an X-linked recessive disorder, which means the gene responsible for hemophilia is located on the X chromosome. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). When a carrier mother (XhX) mates with a healthy man (XY), the possible outcomes for their offspring are as follows: Sons: There is a 50% chance that a son will inherit the X chromosome with the hemophilia allele (Xh) from the carrier mother, resulting in the son having hemophilia (XhY). There is also a 50% chance that a son will inherit the healthy X chromosome from the mother (X) and the Y chromosome from the father (Y), resulting in the son being unaffected by hemophilia (XY). Daughters: There is a 50% chance that a daughter will inherit the X chromosome with the hemophilia allele (Xh) from the carrier mother and a healthy X chromosome from the father (XhX). Therefore, the correct statement is that 50% of sons will have hemophilia.
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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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