Patterns
of Genetic Inheritance—
X-Linked
Inheritance
X-Linked inheritance refers to forms of genetic deafness determined by genes on the X chromosome. The 23rd pair of chromosomes determines the sex of a person. Females have two X chromosomes, one X from each parent. Males have one X chromosome, which comes from the mother, and one Y chromosome, which comes from the father.
If a male has a gene for deafness on his X chromosome, he will be deaf because there is no corresponding hearing gene to “hide” it. If a female has a deafness gene on an X chromosome, she usually has a hearing gene on the other X chromosome to hide its effects. Therefore, females in families with X-linked deafness are usually hearing. However, carrier females have a 1/2 or 50% chance of having deaf sons.
These facts explain why X-linked deafness is more frequently expressed
in males than females and why deaf males in a large family showing X-linked
inheritance are usually related to each other through female relatives.
X-linked genes account for 1-2% of hereditary deafness.
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page—Mitochondrial Inheritance