We have known for the greater part of the 20th century that mammalian females and males differ in both number and kind of sex chromosomes. While females have two X-chromosomes (XX), males have one X- and one Y-chromosome (XY). Both the X and Y carry genes that enhance female and male reproductive function, respectively. Because the Y-chromosome is relatively small and carries only a few genes, this sex chromosome difference means that females essentially have double the number of sex-chromosome genes compared to males. Yet, biochemical evidence indicates that this difference in chromosome number does not result in sex-specific differences in the total amount of X-encoded RNAs or proteins. In other words, female cells with two copies of every X-linked gene synthesized the same amount of protein products as males cells with half the number of genes. For years, this equation puzzled biologists. Clearly, some form of dosage compensation akin to those found in other sexual organisms must exist in mammals.
KeywordsRecombination Retina Lysine Hunt Tated
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- Tagaki N, Abe K (1990) Detrimental effects of two active X chromosomes on early mouse development. Development 109:189–201Google Scholar
- Brown CJ, Ballabio A, Rupert JL, Lafreniere RG, Grompe M, Tonlorenzi R, Willard HF (1991) A gene from the region of the human X inactivation centre is expressed exclusively from the inactive X chromosome. Nature 349:3844Google Scholar