Cell Physiology : Females Are 46,XX; Males Are 46,XY
Heterochromatic: 1. Of or characterized by different colors; varicolored. 2. In genetics, the term refers to regions of chromosomes having little or no gene transcription.
Furthermore, comparisons of the 46,XY male genome with the 46,XX female genome reveal a difference in the kind of sequence between the two chromosomes. The Y chromosome contains a large heterochromatic block (which itself differs in size between individual males), and the X and Y chromosomes differ dramatically in gene content. The X chromosome carries approximately 1,500 genes—about 5 percent of the estimated number of genes in the genome—whereas the Y chromosome carries only 156 known "transcription units,"5 many of which may be nonfunctional pseudogenes.
Pseudogene: A defective segment of DNA that resembles a gene but cannot form a functional gene product.
Given these facts, it is reasonable to ask whether the difference between the sex chromosomes might be responsible for genetic variations in the human population, other than, or in addition to, phenotypic sex.
