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A number of genetic disorders are caused when an individual inherits two recessive alleles for a single-gene trait.

Recessive genetic disorders include Albinism, Cystic Fibrosis, Galactosemia, Phenylketonuria ( PKU ), and Tay-Sachs Disease.

Other disorders are also due to recessive alleles, but because the gene locus is located on the X chromosome, so that males have only one copy ( that is, they are hemizygous ), they are more frequent in males than in females.

Examples include red-green color blindness and Fragile X syndrome.