(Science: genetics) The small chromosome that is male-determining in most mammal species and found only in the heterogametic sex. Thus in mammals the male has one y chromosome and one x chromosome. One region of the y chromosome, the pseudoautosomal region, is homologous to and pairs with the x chromosome. The primary determinant of male sexual development is found on the unpaired, differentiated segment of the y chromosome. It carries few other genes besides those dictating sperm development and triggering appropriate hormonal output. The sex chromosome that is carried by men; human males normally have one x chromosome and one Y chromosome.One of the sex chromosomes that has the genetic information to produce male offspring, that is accompanied by chromosome X. Some inherited characteristics in offspring (such as hairy ears and colour blindness in men) are believed to be sex linked, I.e. in.