X chromosome deactivation (Females have two X chromosomes (One of their X…
X chromosome deactivation
Males have an X and a Y chromosome
Females have two X chromosomes
One of their X chromosomes gets deactivated so makes and females have same number of X chromosomes.
Which X chromosome gets deactivated is random- as see in tortoise shell cats.
X inactivation happens early (when pluripotent cells of ICM are beginning to differentiate)
Mary Lyon, a British geneticist in the 1960's made predictions very close to these (possibly proven?) hypotheses.
The mean % of maternal chromosomes deactivated is 50%
When a cell has switched off a pair of X chromosomes that copy stays switched off for the rest of the woman's life.
There are roughly 1300 genes on X chromosomes
X dosage compensation (X chromosome deactivation) is only in mammals with placentas).
Deactivation is by epigenetics- X chromosome keeps its integrity. No mutations occur.
Despite Mary Lyon's predictions, how X inactivation takes place is still largely unknown.
That X deactivation only happens in X chromsomes and not any of the other 22 autosomes suggests it must be unique in some way.
Around 1300 genes are for the rest of a woman's life, switched off in each of her cells.
Imprinting is much less permanent than X inactivation.
There are only 50-100 imprinted genes in human DNA.
Gene imprinting is about balancing the needs of the paternal and maternal genome. X inactivation is random so mutations in X linked gene decreased.
X deactivation is difficult to study because X inactivation is finely tuned by minute chemical fluctuations and interfering with these without meaning to may result in experimental error.
X and Y chromosomes are thought to have originally been autosomes rather than sex chromosomes as some regions of the DNA are the same on both X and Y chromosomes, just like normal pairs of chromosomes.
Muscle dystrophy- do further research on syntactical muscle tissue.