Female chicks dying one by one, males fine? Ideas?

Ok, I have a pen of 2 frizzle roosters, and a bunch of non related smooth coat frizzles and silkie hens. I get a high rate of frizzle babies. BUT, the female chicks all seem to 'fail to thrive'. They are in the same brooder, same food, same age, but they never get out of the fluff stage. They grow enough wing feathers to show me they are frizzle, then they stop eating, start lingering, and eventually lay down and die!!

There are no parasites, I checked. (small swipe with Ivermectin under wing to be sure)
Not being bullied or crowded. (only 6 chicks in one brooder, 5 in the other)
They come in from the coop the day they hatch, its too cold for the hens to raise em, but I let them sit on them if they want.

I have been raising chicks for years, and these pens have produced countless frizzle babies, but they always seem to be roos....

Has anyone ever heard of a lethal gene being linked to sex? I know it can be linked to color, but these babies are all different colors. I am stumped.... Anyone have any ideas?

Thanks!

 

I swabbed a small amount under the wing of all the chicks when they came in, because I had found some head lice on some of the 4 month olds in the same pen. only way to get rid of these parasites, is to be sure to treat everybody. hatching under a hen exposes chicks to lice and mites, and subsequently your brooding equipment. I treat everybody every 8 weeks out in the coop anyways, but I must have missed some one, and admittedly, I was a little late as I had grown confident that we didnt have any bugs in our coop.... (lol)

It was trace amounts, of a half and half solution, and I have always done it. if you use a cotton swab, it is easy to control the application. an infestation of lice can quickly kill young birds.

regardless, I dont see why an ivermectin solution would only/selectively weaken the females.... which is the real oddity here. I know have two brooders with all young roo's in them. There is one hen chick left, and she is starting to linger.. I have begun feeding crumble soaked in egg yoke, and she likes that , but it looks like that is all she eats.... her crop is always empty, and she just hangs out under the light. The others are starting to be bigger, more feathers etc.....

I dont understand the pattern, why the female frizzles are wasting away.....