Sex Chromosomes – Chromosome Theory and Sex Linkage

00:01 The plus sign is going to illustrate the dominance piece of the puzzle.

00:02 Sex determination in humans, you are probably all fairly familiar with the female has a possibility of contributing X and X and the male could contribute and X or a Y. And the Y chromosome is a little bit special. First of all, it is tiny, but it also has a gene on it that is involved in sex determination. It is called the SRY region of the Y chromosomes.

00:28 It is the sex-determining region of the Y chromosome. And if that gene is present and expressed, then we will see maleness, but if that gene is not present maybe there is no Y chromosome or maybe the gene is broken, then by default we will see the female phenotype in human condition. We know how this works out. We have an X and a Y. We can have male progeny or X is in excess, we have female progeny. Fifty percent chance of boys or girls based on this sex determining system. We will see also in other species that there are different mechanisms going on for sex determination although there are sex determining chromosomes.

01:19 The humans we have X and Y and the birds, we will see as ZW system. The other thing with birds as we see that the homozygous form is the male form. ZZ make birds male and ZW makes birds female. We can also see that in grasshoppers, there is a different situation in which grasshoppers have an XX or an XO. The O means that there is nothing there. It just has one chromosome involved in sex determination whereas honeybees use different systems still.

01:56 The female is diploid whereas the male is a haploid organism, whole other set of chromosomes to become female. That brings us to a little bit of a question and thinking about things