Hemizygous
Hemizygous refers to the presence of only one allele for a characteristic, as opposed to the usual two. This is often the case for genes on the X chromosome in males, who have only one X chromosome and are therefore hemizygous for the genes it carries.
Definition[edit | edit source]
In genetics, a hemizygous organism has only one allele for a particular trait or gene, rather than the usual two. This can occur in several ways, but most commonly it is the result of the organism having only one copy of a chromosome, or a deletion of a region of a chromosome that contains the gene in question. In humans, males are hemizygous for most genes on the X chromosome, because they have only one X chromosome.
Hemizygosity in Humans[edit | edit source]
In humans, males are hemizygous for the genes on the X chromosome because they have one X and one Y chromosome (XY sex-determination system). Females, on the other hand, have two X chromosomes and are therefore not hemizygous for these genes (XX sex-determination system). This has important implications for the inheritance of traits and diseases linked to the X chromosome.
Implications of Hemizygosity[edit | edit source]
The implications of hemizygosity can be significant, particularly in the case of X-linked recessive disorders. Because males have only one X chromosome, they will express the trait or disorder if they inherit one recessive allele. Females, however, must inherit two recessive alleles to express the trait or disorder. This is why X-linked recessive disorders are more common in males than in females.
Examples of Hemizygous Conditions[edit | edit source]
Some examples of conditions that can result from hemizygosity include Hemophilia and Duchenne muscular dystrophy, both of which are X-linked recessive disorders. In these cases, a male who inherits the recessive allele from his mother will have the disorder, while a female must inherit the recessive allele from both parents to have the disorder.
See Also[edit | edit source]
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