sex chromosome

:  a chromosome (as the X chromosome or the Y chromosome in humans) of a sexually reproducing eukaryotic organism that is directly concerned with the inheritance of sex, that contains the genes governing the inheritance of various sex-linked and sex-limited characteristics, and that is represented differently in the two sexes either by being present in one and not the other or by being present a different number of times in one sex compared to the other—called also heterochromosome