Sex-linked inheritance

Mutant genes causing sex-linked diseases are located on X chromosome. Since every woman has two X chromosomes and every man one X chromosome and Y chromosome there are different phenotypes depending on the sex. Man are ill when they receive the mutant gene while woman can still get a functional copy from the second parent. Among women different phenotypic effects result from the random inactivation of one of the X chromosomes. Ill father do not transmit mutant gene to his sons but it passes to every of his daughters. For sex-linked dominant diseases both sexes are affected. Characteristic things is that there is no man-to-man transmission.