Define Sex Linkage

Genes found on the sex chromosomes are referred to as having a sex linkage. Since the inheritance and expression patterns of these genes vary between males and females, they are considered sex-linked. While sex linkage and genetic linkage are distinct concepts, sex-linked genes can have genetic linkages.

Sex linkage was discovered by Thomas Morgan in 1910, who witnessed an inordinate proportion of white-eyed male fruit flies (Drosophila melanogaster). In Morgan’s experiment, these mutated white-eyed male fruit flies were crossed with pedigree red-eyed female fruit flies. The outcome was predominately red-eyed flies of both genders. These individuals generated some white-eyed male flies when they were crossed, but no white-eyed female flies.

When a gene mutation (allele) is located on a sex chromosome (allosome), as opposed to a non-sex chromosome (autosome), the resulting sex-specific features of presentation and inheritance are referred to as being “sex-linked”. Humans refer to these as X-linked recessive, X-linked dominant, and Y-linked. Depending on the sex of the parent and the child, all three have different inheritance and presentation patterns. This is how they distinguish themselves from recessiveness and autosomal dominance.

An individual’s gender is determined by their sex chromosomes. The sex chromosomes in mammals and humans are X, and Y. Males have an X and a Y chromosome, whereas females carry two X chromosomes.

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