bio (0310) - BoL: sex-linked genes

some alleles can only be found on the sex chromosomes: X and Y

note that the Y chromosome is significantly shorter than the X chromosome (this could be due to some kind of evolutionary change) and as a result carries less alleles.

also, as a result, it means if there is an allele for a certain trait or disease on the X chromosome for a man, there would be nothing on the Y and the X would determine stuff. catch it? because of this, men can't carry certain things, they can either just have the disease or not.

if you try draw punnet squares for two alleles and sex-linking them.. the result is 4 babies, with 2 male and 2 female, and the genotypes mixed accordingly. not that 4 babies are born, that's just the chance.

this is hard to explain.. but i understand it so that's what's important hahaha.

there are cases that a trait can be carried on the Y only, but it's not taht common. it's usually on the X since the X is the epic long one.

in the case of recessive diseases. this is why females can carry the disease but not necessarily have it. if they had a heterozygous pair-up for that disease, it'd mean they can carry the disease but not have it.

in the case of men, if they received one of the X chromosomes from their mother (they'd have to since they receive Y from their father) then either they have it (receive recessive gene, nothing on Y to counter it) or they dont (receive dominant gene, no issue there)