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:

Allele — An allele is a viable DNA (deoxyribonucleic acid) coding that occupies a given locus (position) on a chromosome. Usually alleles are sequences that ...  > read more

Sex — Sex refers to the male and female duality of biology and reproduction. The concept is confined to organisms that reproduce ...  > read more

Trait (biology) — In biology, a trait or character is a feature of an organism. The term phenotype is sometimes used as a synonym for trait in common use, but strictly ...  > read more

Haemophilia — Haemophilia or hemophilia is the name of any of several hereditary genetic illnesses that impair the body's ability to control bleeding. Genetic ...  > read more

Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.

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