Sex-Linked Traits

What do you think the term sex-linked traits means? Journal What do you think the term sex-linked traits means?

Humans 22 pair of autosomal chromosomes 1 pair of sex chromosomes

Sex Chromosomes Females XX Males XY

The genes located on the X and Y chromosomes show a pattern of inheritance called sex-linked. A sex-linked gene is a gene located on a sex chromosome. Genes on the Y chromosome are found only in males and are passed directly from father to son. Genes located on the X chromosome are found in both sexes, but the fact that men have just one X chromosome leads to some interesting consequences. In humans the X-chromosome is much larger than the Y chromosome and contains thousands of genes more than the Y chromosome.

Sex-linked traits are those carried on the X or Y chromosome. A normal female has two X chromosomes. One from each parent A normal male inherits an X chromosome from the mother and a Y chromosome from the father. Therefore, normal males inherit sex-linked traits only from their mothers.

For each of the genes that are exclusively on the X chromosome: females, who are XX, would obviously have two alleles Males, who are XY, would have only one allele. Therefore, females with one recessive allele and one dominant allele for a gene that is unique to the X chromosome will display the dominant phenotype. A male with a recessive allele for a gene unique to the X chromosome will always exhibit that recessive trait because there is no other corresponding allele on the Y chromosome.

Colorblindness For example, humans have three genes responsible for color vision, all located on the X chromosome. In males, a defective allele for any of these genes results in colorblindness, an inability to distinguish certain colors. The most common form, red-green colorblindness, occurs in about 1 in 12 males. Among females, however, colorblindness affects only about 1 in 200. In order for a recessive allele, like colorblindness, to be expressed in females, it must be present in two copies—one on each of the X chromosomes. The recessive phenotype of a sex-linked genetic disorder tends to be much more common among males than among females.

Duchenne Muscular Dystrophy Sex-Linked Disorders Hemophilia Colorblindness Duchenne Muscular Dystrophy

Hemophilia A disorder affecting human blood clotting Defective allele prevents the synthesis of a factor needed for blood clotting

Colorblindness Prevents humans from distinguishing between different colors

Duchenne Muscular Dystrophy Condition in which muscles begin to degenerate in childhood

XHXH Chromosome with normal dominant allele female Non-hemophilia Normal types—wild type

XhXh Chromosome with recessive hemophilia allele female

XHXh Chromosome with heterozygous allele female; carrier Non-hemophilia

XHY Chromosome with normal dominant allele male Non-hemophilia Wild type (normal)

XhY Chromosome with recessive hemophilia allele, male