Sex differences in hereditary disorders

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 The other major type of chromosomal abnormality is the hereditary type.  One or several genes can be mutant on any chromosome.  When the disease-producing (pathogenic) gene is on any of the first 22 chromosome pairs,  the disorder is termed autosomal (having to do with the self).   When the mutant gene or group of genes is situated on one of the chromosomes of the 23rd pair (on the X or Y chromosome)  the mode of transmission is termed gonosomal (having to do with one's gender).   In a sense the term gonosomal is a misnomer because the X gonosome is responsible for many other things besides gender.   The Y chromosome, on the other hand, is not very important,  aside from the determination of maleness, and can be dispensed with entirely (Turner syndrome).   When the mutant gene is situated on chromosome X,  it will affect male offspring more than it does female offspring.    This is because the second X chromosome of females is able to inhibit the effect of the pathogenic gene.   An X-linked hereditary disease is transmitted from mother to son.  It usually affects all the daughters of an affected father, but it affects the daughters subclinically (below the threshold of diagnosis) more often than it does the sons.  Diseases which are X linked and well known include hemophilia,  daltonism,  Duchene's muscular dystrophy.