SEX-LINKAGE: what is sex linkage?

Genes that are located on one of the sex chromosomes are said to be sex linked. Sex  linkage results in an inheritance pattern different from that shown/of genes carried on autosomes (chromosomes other than sex chromosomes). Sex linked genes may be on the X-chromosome, hence, they are called X-linkage or on the  Y- chromosomes called Y-linkage.
X-linkage, because the X-chromosome is much larger than the Y-chromosome. Most sex-linked genes are located on the X-chromosomes. In addition to carrying genes that are concerned with the determination of female sex characteristics, the X-chromosome also carries genes for non-sexual characteristics. Such as ability to see particular colours, ability to clot blood efficiently among other traits. In X-linkage, recessive allele is expressed more often in males than in females because the heterogametic sex o.e male carry only one allele for an X-linked gene whereas the homogametic sex (females) have alleles for the gene to be manifested phenotypically.
Thus, a female with one recessive allele on  one of her X-chromosomes will not be affected by it. However, a male with a recessive allele on his X-chromosome has no dominant allele to manifest phenotypically on the presence of a single allele.

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