(Part I can be found here) Now the alleles which determine biological sex are found on the last pair of chromosomes, what are called the sex chromosomes. Like most chromosomes, the primary one with regard to sex is X shaped, just like all other chromosomes. This is the one commonly referred as the X chromosome, though all chromosomes are shaped in an X. There is one exception to this rule, the Y chromosome, or a short, compact chromosome with one branch missing. This is normal; nearly every sexually dimorphic vertebrate has this arrangement. It does not make males "inferior" or "damaged women" like many gender ideologues would say. It is just the way that nature codes for the expression of male sex characteristics. What we do know is that the Y chromosome is dominant; any normal pairing of an X and Y chromosome will result in a male expression of the genome. This means you do not need two Y chromosomes to be male; you only need one. Women, who do not have a Y chromosome, code as XX, or two recessive X chromosomes. Furthermore, the Y chromosome is not the thing, necessarily, that makes you your father's son. Your father certainly gave it to you, but your looks, height, body type, intelligence and other things are found elsewhere in the genome. In the production of gametes, each diploid parent produces haploid gametes, which contain 23 chromosomes, one half of the pairs. For the male, approximately 50% of his gametes possess the Y chromosome, while approximately 50% contain the X chromosome. The female, however, only produce gametes with the X chromosome (since she has no Y chromosome). So we can show the expression of sex in the same exercise we did in Part I, between a male (XY) and a female (XX) from generation F1 to F2: F1: XY + XX F2: 50% probability of XX (female expression) and 50% probability of XY (male expression) We find that this does not change between F2 and F3. The nature of sexual reproduction precludes the more complicated, interactive genetic permutations that we found with eye color. But one thing stays the same between the genes that express eye color and the genes that express sex; the presence or absence of one allele does not necessarily indicate that the parent who possessed the allele did not reproduce, and did not have sex. It only means that the allele or chromosome you are looking at did not, by random chance, express itself. A man, for example, could be very reproductively successful, siring many sons and many daughters. But if all you are interested in is whether his Y chromosome is widely dispersed among people today, there is a good chance that it might not be, and for normal reasons of mendelian variability alone, irrespective of hypergamy.

In the next section, we will examine how the Y chromosome becomes expressed and eliminated from a population.