Knock out mice - (Dec/10/2005 )

Here's my basic question.

If you want to create a double-knockout, why do you have to have both genes that you're knocking out on different chromosomes? Someone told me, if they're not, then you can only rely only on crossingover (which is rare?). I guess I just don't understand the basics of generating knockouts.

Thanks!

hi
if you have genes on the same chromosome : you have 50% chances to have the genes knocked down on the same chromosome (lets take "ab" as a notation for the two genes) . ok with this?

2nd step : cross the F1 generation : you need to have 2 mices that carries the chromosome ab

......AB.......ab
AB....AB/AB....AB/ab
ab....ab/AB....ab/ab


so only ¼ to get the good mice.
assuming you have only 50%to have AB/ab mice (instead of having Ab/aB mouse) for both « parents » only 25% of F1 generation may drive the second process.
so 25% in both steps means roughly only 6% to have 1required mouse.
so to be sure getting theorically 1mouse you need to screen 20mouses from 1 couple.
that’s impossible for a mouse to carry 20embryos

Nope--still a bit confused! Can you explain a bit more, PLEASE!!!