How is X inactivation determined?
By Matthew Alvarez
How is X inactivation determined?
X-chromosome inactivation occurs randomly for one of the two X chromosomes in female cells during development. Inactivation occurs when RNA transcribed from the Xist gene on the X chromosome from which it is expressed spreads to coat the whole X chromosome.
What is XCI in genetics?
X chromosome inactivation (XCI) is a dosage compensation process that was adopted by female mammals to balance gene dosage between XX females and XY males. XCI starts with the upregulation of the non-coding RNA Xist, after which most X-linked genes are silenced and acquire a repressive chromatin state.
What are the three phases of X chromosome inactivation?
Timing
| Process | Mouse | |
|---|---|---|
| 1 | Zygotic genome activation | 2–4 cell stage |
| 2 | Imprinted (paternal) X-inactivation | 4–8 cell stage |
| 3 | X-activation | Early blastocyst stage |
| 4 | Random X-inactivation in the embryonic lineage (inner cell mass) | Late blastocyst stage |
What is X-inactivation or Lyonization?
Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, while males have one X and one Y chromosome. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in cells other than egg cells. This phenomenon is called X-inactivation or lyonization.
What is X-inactivation of the X chromosome?
X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells.
How common is skewed X-inactivation in the US?
Our collective data suggest that skewed X-inactivation is common in the general population. This may contribute to manifestation of symptoms in carriers of recessive X-linked disorders. We recommend that X-inactivation results should not be used lightly in the interpretation of X-linked variants.
What is an example of X inactivation in cats?
A classic example of X-inactivation is seen in cats. If a female cat is heterozygous for black and tan alleles of a coat color gene found on the X, she will inactivate her two Xs (and thus, the two alleles of the coat color gene) at random in different cells during development.
