Figure 5.4 Sex (X)-linked inheritance: (A) males reproduce; (B) males do not reproduce.

enzymatic defect as well as the extent of exposure to therapeutic agents and other environmental agents. The incidence of sex-linked recessive inheritance is very much higher in males than in females. For rare sex-linked traits, parents of affected males are normal, and the only affected relatives are maternal uncles and other male relatives in the maternal ancestry. If an affected male can reproduce, all of his male offspring are unaffected, but all of his daughters are heterozygous carriers. In case the affected male dies before reproducing, or is sterile, transmission is solely by carrier females.

The segregation frequencies expected among offspring of autosomal and sex-(X)- linked traits are summarized in Table 5.5.

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