Sex linkage is the phenotypic expression of an allele that is dependent on the gender of the individual and is directly tied to the sex chromosomes.

In such cases there is a homogametic sex and a heterogametic sex.

In mammals the homogametic sex is female (XX) and the heterogametic sex is male (XY), thus the sex linked genes are carried on the X chromosome.

In birds and in some insects the homogametic sex is male.

In regards to ducks, a drake has ZZ chromosomes, with females ZW, sex-linked any recessive sex-linked genes are at least in part on the Z chromosome, and "male" and "female" are exchanged for humans..

For more information about the topic Sex linkage, read the full article at Wikipedia.org, or see the following related articles:

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