In: Biology
Genetic Development
Describe the process of X-inactivation. How does it occur and why is it necessary?
What is the concept of genomic equivalency?
Mammalian X-chromosome inactivation is initiated from X-inactivation center or XIC, which is located on long arm of X chromosome. The X-inactivation center contain 12 genes, seven of which code for proteins, five for non-coding RNAs, of which only two are known to play active role in X-inactivation process, XIST and TSIX. The roles of XIST and TSIX appears to be antagonistic. The XIST gene does not encode a protein but rather produces a long coding RNA. XIST RNA is only expressed in cells containing at least two Xs. XIST RNA is expressed from inactive X chromosome and coat the chromosome from which it was produced. Like XIST, TSIX also acts on the chromosome that produces it. TSIX is antisense to XIST and is transcribed in opposite direction across the entire XIST gene.
Genome equivalency is the process by which the expression level of sex-linked genes are layered in one sex to offset a difference in sex-chromosome number between females and males of a heterogametic species.