What does is mean when aspergers syndrome is x-linked?

Answer 1

To be "x-linked" means that a trait is carried on the X-Chromosome.

Recall that each child receives one chromosome from each parent, a male receiving one X and one Y -chromosome, and a female receiving two X -chromosomes.

Because the male receives only one X-chromosome, he only need receive one X with a particular trait to be affected, whereas the female would need two Xs with traits to be affected.

So, Asperger's Syndrome is more prevalent among males, as they only need receive one X-chromosome with Asberger's on it.

This Asperger's-X must be from the mother, as the father would give the Y-chromosome required for a male. Since the mother has two X-chromosomes that might be affected (depending on if she has the Syndrome, or is just a carrier), there is a 75% chance the male will have Asperger's Syndrome if the mother has at least one Asperger's-X.

Conversely, a female must have one Asperger's-X from each parent, so if the mother has two Asperger's-X -chromosomes, the daughter will still only be a carrier (and so not have Asperger's Syndrome), if the father also carries the trait on his X-chromosome.