If you knocked out the gene Xist in a cell line derived from

If you knocked out the gene Xist in a cell line derived from a female mouse, would you expect to detect higher, lower or unchanged expression of X-linked genes? Explain! What if you instead knocked out the gene Sxl in a cell line derived from a female Drosophila? Would you expect higher, lower or unchanged expression of X-linked genes? Explain!

Solution

Answer 8 a) - Xist gene in female mouse stands for \"X inactive specific transcript\" and is a part of the Xic \" X chromosome inactivation centre\". This gene is majorly responsible for the inactivation of the X chromosome in females which could then have an effect on the phenotype of female mice. If the Xist gene is knocked off, then Xic complex will not form and hence \"X\" chromosome in female is not inactivated. This implies that the genes linked to X chromosome functions normally. Thus, there would be no change in the expression of X-linked genes.

b) Sxl gene in Drosophila melanogoaster stands for the Sex lethal gene and plays a crucial role of sex determination in the fruit fly. When Sxl gene is active, its products cause somatic cells to establish a female identity which is then maintained over the course of time through the controlled expression of Sxl gene. However, since there are 2 copies of the X chromosomes in females, active Sxl gene ensures that the transcription of the X-linked genes is low; which is typical and necessary for the females having 2 copies of the X-chromosome. If the Sxl gene is knocked off, the Sxl becomes inactive/is not transcribed, thus somatic cells move onto male differentiation and a high level of X-linked genes\' expression is observed.