As a corollary, in females whose karyotype shows the presence of more than two X-chromosomes there is more than one Barr body and males who have XXY chromosomal constitution also have a Barr body. Irrespective of the presence of Y chromosome a Barr body is found whenever there is more than one X chromosome. One finds that the number of Barr bodies in a cell is (n-1) where n is the number of X-chromosomes. It was also known that mice with only one X-chromosome were normal females, thus suggesting that one X-chromosome is sufficient for female development. Considering all these observations Mary F Lyon from England put forward the well known Lyon hypothesis, which addresses the issue that females have twi