And the other sex chromosome is called the Y chromosome. And notice it's much smaller in size and has a slightly different shape than the X chromosome. So, in contrast, male individuals have one X chromosome that contains many different types of genes that code for specific sex link traits and it also contains a small Y chromosome that basically has one or several genes that code for maleness. Why is that? Well, it's because the Y chromosome actually determines what the gender of that particular individual is. So to see what we mean, let's take a look at the following diagram.