[kc0bfv]

Hrm, if you're a girl, you get 1 X from Mom and 1 from Dad. So, if Mom's X's are chromosomes a and b, and Dad's is chromosome c, then your X chromosomes will be a,c or b,c with a .5 prob for each. With your suggestion, there's a .5 prob in each case that Dad's X will be used, and so a .5 prob overall that, for a girl, Dad's X will be used.

A guy has to use Mom's X. I think the paper's argument still holds, because there's a larger amount of possibilities for women than men, but I can't take this much further without circular reasoning.

[kc0bfv]

Oh, for the women there's a .25 prob that a is used, and a .25 prob that b is used, and a .5 prob that c is used. Dad's X has the best chance, and his X may have made him a better partner than his peers. Also, a .25 prob for the X that made Mom a better partner. So, a .75 prob overall of getting a great X and a .25 prob of getting an unknown X.

For the dude there's a .5 prob of getting a great X and a .5 prob of getting an unknown X.