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View Full Version : Not satisfied with textbook explanation of X chromosome deactivation


1MileCrash
Apr20-11, 05:24 PM
According to my biology textbook, calico cats get their fur color mosiac from the random deactivation of one of their X chromosomes, by condensing them into barr bodies and displaying either the maternal or paternal X chromosome fur color only. IE each cell randomly deactivates either X and displays the remaining phenotype.

If this deactivation were truly random, why would their be black and yellow "patches" of fur on the cat? If it were truly random, and each had an equal chance, I would expect a cat that almost consisted of one fur color to the human eye because of an equal distribution and number of cells that deactivated maternal vs. paternal X and vice versa.

Ygggdrasil
Apr20-11, 05:44 PM
The x-chromosome inactivation occurs during the development of the embryo when not all the cells are finished dividing. Because x-chromosome inactivation is passed onto the daughter cells after cell division (e.g. the daughter cells will have the same x-chromosome inactivated as the parent cell), all the cells derived from that progenitor cell will have the same x-chromosome inactivated and have the same color. Thus, all the cells in one patch can trace their lineage back to the same cell in the embryo.