Sex linkage

Sex linkage is the inheritance pattern of genes located on a sex chromosome. Their transmission and expression can differ between sexes because sex chromosomes are not present in the same combinations in all individuals.

X-linked inheritance: The inheritance of genes located on the X chromosome. Most classic human examples of sex linkage involve genes on the X chromosome.
Red–green color blindness: A group of color-vision deficiencies that impair discrimination between red and green hues. Common red–green deficiencies illustrate recessive X-linked inheritance in humans.
Thomas Hunt Morgan: An American geneticist whose fruit-fly experiments established links between genes and chromosomes. Morgan's experiments provided decisive evidence for sex-linked inheritance.
Autosomal inheritance: The inheritance of genes located on non-sex chromosomes. Autosomal genes generally do not show the sex-specific transmission routes characteristic of sex linkage.
Y-linked inheritance: The inheritance of genes located in the non-recombining regions of the Y chromosome. Y-linked traits pass through the father-to-son route unavailable to X-linked genes.
Hemophilia A: An inherited bleeding disorder caused by insufficient or defective clotting factor VIII. Its X-linked recessive inheritance historically revealed how traits can track through maternal lines.
Drosophila melanogaster: A fruit fly widely used as a model organism in genetics and developmental biology. Its visible traits and short generation time made sex-linkage experiments practical.
Sex-limited trait: A trait whose phenotype is restricted to one sex, though its genes may be present in both. Sex-limited expression can resemble sex linkage even when the gene is autosomal.
Hemizygosity: The state of having only one copy of a gene in a diploid organism. Many XY individuals are hemizygous for X-linked genes, so recessive alleles can be expressed.
Duchenne muscular dystrophy: A progressive muscle-wasting disorder caused by pathogenic variants in the DMD gene. The DMD gene's X-linked inheritance gives this disorder a characteristic family pattern.

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