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Question
Why do men suffer from hemophilia and colour blindness? Under what conditions do women suffer from these disorders?
Solution
Hemophilia and colour blindness are sex-linked disorders, caused by recessive genes located on X-chromosome. These disorders occur more frequently in men because males are heterozygous for the defect. They have one X-chromosome and one Y-chromosome. Y- chromosome does not carry alleles for these traits, therefore the recessive genes are able to express even in a single dose.
Females have two X-chromosomes therefore both the alleles have to be present in the recessive form to be able to be expressed. Thus, females suffer only if they are homozygous for the trait which is possible only when a carrier or sufferer female marries a sufferer male.
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