MadSci Network: Cell Biology |
Dear Sumnima, The question that you ask is really interesting because it has direct application for the upcoming Olympics games. One of the ways that the gender of a female athlete is ascertained is by taking a scraping of the lining of the cheek and examining the cells under the microscope. As you correctly pointed out cells from a female possess two X chromosomes whereas cells from a male would possess a single X and a Y chromosome. It is great to know that bit of information, but you need to look a little further about chromosomes. Unless the cell is undergoing mitosis (or meiosis in the case of gametes), the chromosomes of these cells are mostly unwound. You can think of them as a long piece of yarn that, instead of being rolled into a ball, is loosely arranged in the nucleus. This is true for all of the chromosomes, except for the second X chromosome of the female. It is present in its condensed state, that is it is wound up in a little ball. So when you look at the nucleus of the cheek cells, most of the female's cheek cells will have a little dense, dark spot at the periphery of the nucleus, whereas only a few of the male's cheek cell nuclei will have one of those little spots. These little spots are known as "sex chromatin" or "Barr body." So the cell itself is not darker, only that little spot in the nucleus is darker. Although you didn't ask, all of the females cells that have nuclei will exhibit a sex chromatin and if you look at a female's neutrophil, one of the white blood cells, the sex chromatin is located in an outpocketing of the nucleus. This outpocketing resembles the drumstick of a chicken and is referred to as the "drumstick." I hope this helps. Good luck. Leslie P. Gartner, Ph.D. Associate Professor of Anatomy Dental School University of Maryland
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