|MadSci Network: Genetics|
Would there be a barr body in an individual with a single X chromosome? Before I give the answer, let's review why any cell would have a Barr Body. Mammalian females have two X chromosomes while males have an X and a Y. In order to balance out the gene dosage of genes on the X chromosome between males and females, females silence all but one of their X chromosomes. The key phrase there is "all but one", as opposed to one of their chromosomes. So if a female had three X chromosomes due to non-disjunction in the parent, she would silence 2 Xs in all her cells, leaving one active. When X chromosomes are silenced, they condense into a dense ball of protein and DNA which is what we see under the microscope as a Barr Body. So, the answer is, if a person (male or female) has only a single X chromosome, then no, it would not be silenced and packaged as a Barr Body. It needs to be active, since the person needs their genes on the X in order to develop and live and be healthy. Now, how exactly the X becomes silenced and how the cell knows to count Xs and leave a single one unsilenced, and which one, are all exciting areas of current research.
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