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Sex Chromosomes Chromosomes are the aggregates of genes, carrying heredity information. They comprise of proteins and DNA, and are located within the cells' nucleus. Human cells contain 22 pairs autosomes and only one pair of sex chromosomes. These sex chromosomes, the X and the Y chromosomes determine the sex of the individual, or the gender. In such a way, there are two sex chromosomes in a human somatic cell: XX in female and XY in male. A human germ cell contains only one sex chromosome, which is X or Y in a males sperm, and X in an females egg.
When an X-sperm combines with an egg, the resulting fertilized egg, or zygote, will have two X chromosomes (Cells and Viruses > Sex Chromosomes). The individual that develops from this XX-zygote has the characteristics of a female. At the same time, when an Y-sperm combines with an egg, the resulting fertilized egg, or zygote, will have X and Y chromosomes. The individual that develops from this XY-zygote has the characteristics of a male. A female usually has XX chromosomes, and a male usually has XY chromosomes. Yet, sometimes occurs that both female and male characteristics are found in one person, and there can be a male with XX chromosomes, and a female with XY chromosomes.
The scientists have made a research, and have found some molecules that also influence the determination of sex. One of such molecules is SRY (that stands for sex-determining region Y gene) is in Y chromosome. SRY molecule binds to the other DNA in the cell and changes the shape of DNA. By doing this, it alters the DNA properties and the expression of a number of genes, resulting in testis formation. As it occurs, most men with XX chromosomes still have a copy of this SRY gene on one of their X chromosomes, and this copy of SRY accounts for their maleness. Yet, as they have no remainder of the Y chromosome, XX males rarely develop secondary sexual characteristics in the usual way (Cells and Viruses > Sex Chromosomes).
Works Cited Cells and Viruses > Sex Chromosomes. 3 February 2008 < web >.
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