BIOL 2500 Lecture Notes - Lecture 4: Xist (Gene), Murray Barr, Barr Body

• School: University of Manitoba
• Department: Biological Sciences
• Course: BIOL 2500
• Professor: Roman Gietz

Document Summary

In organisms with sex chromosomes, there is a gender imbalance between the copy number of genes on the sex chromosome. Any mechanism that compensates for the difference in number of copies of genes between males and females is called dosage compensation. There are at least three different mechanisms of dosage compensation. Early in mammalian development, one of two x chromosomes in each female somatic cell is randomly inactivated. The random x inactivation hypothesis is also called the lyon hypothesis after mary lyon who. The inactive x chromosome is visible near the nuclear wall, as a condensed barr body, rst visualized by murray barr. Once x inactivation has occurred in a cell, it is permanent in all descendants of that cell. Female mammals are mosaics of two populations of cells, one expressed the maternal x and the other the paternal x. Alleles of both chromosomes are expressed approximately equally over the whole organism.