Like the X chromosome, the Y chromosome exhibits a particular pattern of inheritance because of its association with the male sex. In humans and other mammals, all embryos initially develop immature internal sexual structures of both females and males. SRY, a gene in the Y chromosome, encodes a protein that is the trigger for male development. (“SRY” stands for “sex-determining region in the Y chromosome.”) In the presence of SRY, male structures complete their development and female structures degenerate. In the absence of SRY, male embryonic structures degenerate and female structures complete their development. The SRY gene is therefore the male-determining gene in humans and other mammals. Because they are linked to SRY, most genes in the Y chromosome show a distinctive pattern of inheritance in pedigrees, different from the patterns of autosomal genes Mendel observed in his pea plants, in that they are transmitted only from father to son.