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X-inactivation happens randomly in development of XX humans. If it occurred at the one-cell stage (immediately after fertilization before any cell divisions occur in the embryo), What would be the best prediction for the offspring of an XX female affected for an X-linked dominant trait? Assume this individual has 10 offspring. Select the best answer.

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Answer: The best prediction for the offspring of an XX female affected for an X- linked dominant trait would be an equal probability of inactivation, since the maternal and paternal X chromosomes have the same probability. However, the occurense of this disorders in female is much lower than that. So, if the female generates female offpsring they would have a less chance of developing X-linked disorders than the male offspring.

Explanation: The difference between the two genders odds happens because, 12 to 20% of genes on the inactivated X chromosome remain expressed, providing females with added protection against defective genes coded by the X- chromosome. The time period for X- chromosome inactivation explains this disparity between genders. A female affected for an X-linked dominant trait would have about half or her liver cells working perfectly, which is typically enough to ensure normal blood clotting. It could result in more dysfunctional cells. However, such statistical extremes are unlikely. Genetic differences on the chromosome may also render one X- chromosome more likely to undergo inactivation.

Although inactivation is initially random, cells that inactivate a normal allele will eventually be overgrown and replaced by functionally normal cells in which nearly all have the same X- chromosome activated.

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