The sex of the individual is determined by sex chromosomes in humans, as well as in many other animals and some plants. The sex chromosomes are one couple of non-homologous chromosomes. Up to now, we now have just considered inheritance habits among non-sex chromosomes, or autosomes. In addition to 22 homologous pairs of autosomes, individual females have homologous couple of X chromosomes, whereas peoples men have actually an XY chromosome pair. The Y chromosome is much shorter and contains many fewer genes although the Y chromosome contains a small region of similarity to the X chromosome so that they can pair during meiosis. Each time a gene being examined exists from the X chromosome, yet not from the Y chromosome, it is stated to be X-linked.

Figure 1. In Drosophila, the gene for attention color is found in the X chromosome. Clockwise from top left are brown, cinnabar, sepia, vermilion, white, and red. Red attention color is wild-type and it is principal to eye color that is white.