Of a normal couple, half the sons are hemophiliac while half the daughters are carriers. The gene is located on:
Correct answer: C. One X-chromosome of mother
- A. X-chromosome of father
- B. Y-chromosome of father
- C. One X-chromosome of mother
- D. Both X-chromosomes of mother
Explanation
The gene for hemophilia is located on one of the X-chromosomes of the mother, making her a carrier. A cross between a carrier female (XhX) and a normal male (XY) results in 50% of the sons (XhY) being hemophiliac and 50% of the daughters (XhX) being carriers. The father cannot pass the X-linked hemophilia gene to his sons, as he contributes a Y-chromosome to male offspring. Thus, the gene is not on the father's X-chromosome or the Y-chromosome. Additionally, if both of the mother's X-chromosomes carried the hemophilia gene, she would be affected, not just a carrier.
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About Inheritance
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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