X-linked+recessive

=X-linked recessive=

**X-linked recessive** is a pattern of inheritance involving a recessive allele that is carried on an X chromosome. Sex-linked recessive diseases include Duchenne muscular dystrophy, haemophilia and Red-Green colour blindness.

The pedigree below is typical of an X-linked recessive pattern of inheritance:



There are multiple hallmarks of an X-linked recessive pattern of inheritance, notably:


 * **Such disorders mainly affect males,** since males need inherit only one copy of the allele (on their single X chromosome), while females need two copies.


 * **Male-to-male transmission is impossible** because only the Y chromosome is passed down the paternal-son line.


 * **Affected males are often born to unaffected parents. All affected males are related through their mothers. **


 * **Affected females require both an affected father and a mother who carries the allele on one of her X chromosomes. **

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 * **The trait or disease is typically passed from an affected grandfather, through his carrier daughters, to half of his grandsons. **