the underside extends up to half way on the sides of the body and the lower base of the neck of males is white. The white eye ring is broad all around the eye with the leg-stripe going only down to the shanks. Genetics The blackbuck shows variation in its diploid chromosome number. Males have 31-33, while females have 30-32. Males have an XY1Y2 sex chromosome. Unusually large sex chromosomes had earlier been described only in a few species, all of which belonged to Rodentia. However, in 1968, a study found that two artiodactyls, the blackbuck and the sitatunga, too, showed this abnormality. Generally, the X chromosome constitutes 5% of the haploid chromosomal complement, but the X chromosome of the blackbuck this percentage is 14.96. Portions of both peculiarly large chromosomes show delayed replication. A 1997 study found lower variation in blood protein polymorphism in Antilope in comparison with Antidorcas, Eudorcas, and Gazella. This was attributed to a history of rapid evolution of an autapomorphic phenotype of Antilope. This might have been aided by a particularly strong selection of a few dominant males due to their lekking behaviour. Characteristics The blackbuck is a moderately sized antelope. It stands up to high at the shoulder; the head-to-body length is nearly . In the population introduced to Texas, males weigh , an average of . Females are lighter, weighing or on average. Sexual dimorphism is prominent, as males are heavier and darker than the females. The long, ringed horns, that resemble corkscrews, are generally present only on males, though females may develop horns, as well. They measure , though the maximum horn length recorded in Texas has not exceeded . The horns diverge forming a "V"-like shape. In India, horns are longer and more divergent in specimens from the northern and western parts of the country. The white fur on the chin and around the eyes is in sharp contrast with the black stripes on the face. The coats of males show two-tone colouration; while the upper parts and outsides of the legs are dark brown to black, the underparts and the insides of the legs are all white. Darkness typically increases as the male ages. On the other hand, females and juveniles are yellowish fawn to tan. In Texas, blackbuck moult in spring, following which the males look notably lighter, though darkness persists on the face and the legs. On the