Fawn babies from Gray zebras.

Learn about mutations and expected breeding outcomes.
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Sally H
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Fawn babies from Gray zebras.

Post by Sally H » Tue Mar 14, 2006 2:24 pm

From another thread, quoting Crystal.


They start their first molt when they are about 2 months old. Fawn is a sex-linked recessive trait, so if two of the chicks are fawn, it is likely that your cock bird is carrying the fawn gene on one of his "X" (Z) chromosomes. His other "X" (Z) is gray, which is why he does not appear fawn. If the babies really are fawn, those two chicks will be hens. The grey chicks could be either sex.

Okay, thats the second time I read that about it coming from the male and that the fawn chicks will all be female. Why? How do you get a fawn male? One of these babies and another male that has the fawn gene?

How about that lighting thing to influence the sex of the clutch? If somehow I could increase the chance of male offspring, that would only decrease the chance of fawns, right?

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Crystal
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Post by Crystal » Tue Mar 14, 2006 3:26 pm

The trick to fawn is that it is recessive (so it is "hidden" or "overridden" by dominant traits, such as gray), AND sex-linked, or located on a sex chromosome (the human "X" or the avian equivalent, "Z"). Birds are the opposite of mammals in the respect that the FEMALE (hen) is "XY" (ZW) and the MALE (cock) is "XX" (ZZ). This means that the hen will show a recessive sex-linked trait when only one copy is present, because she only has one "X" and no other "X" to override the recessive gene.

The cock on the otherhand has two X's, so he can have one carry a "hidden" recessive gene, and the other cary the dominant, phenotypically visible gene.

Each baby receives one copy of a sex gene from each of its parents--one from the hen and one from the cock. The cock can donate one of his two X's, the hen can either donate her X (producing cock babies) or her Y (producing hen babies).

In the case of your cock, he is carrying one fawn X and one gray X. Only the gray shows up because the fawn is recessive to the gray; they gray overrides the fawn.

The reason he is able to produce fawn daughters is because some of his daughters will inherit the fawn X (and some will inherit the gray X); the Y gene from the mother hen does not carry information for color, so you get what the cock passes on--hens carrying a fawn X (their only X) will appear fawn and hens carrying a gray X (their only X) will appear gray.

To get a fawn cock, you need to produce a bird that is carrying TWO fawn X chromosomes. You could breed one of the fawn hens you have produced to a fawn cock, or a split for fawn cock like their father (although I highly recommend NOT inbreeding daughters back to fathers). Breeding a fawn hen to a split for fawn cock will produce some fawn cocks and some gray cocks which are split for fawn.

If you could influence sex, producing more males would produce fewer fawn babies, since the only fawns you can get from a split fawn cock X gray hen are fawn hens. The males produced however could either be gray and not carrying any fawn gene or gray and split for fawn.

I hope that answers your question! Let me know if you are still confused. :)

Sally H
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Post by Sally H » Tue Mar 14, 2006 7:11 pm

I think I'm getting it. So my lil Fawn hens have XY so they would be passing the fawn gene to their male offspring but if her cock mate was a true gray she would never produce fawn babies because her fawn X is continually overridden by the cock's gray X X's. Her male chicks would be "split" to fawn? All of them? I guess there is no way to look at a zebra cock and know if there is any fawn in one of his X's.

And no, I would never inbreed my zebras. I am having such a good time watching them raise their chicks, I wouldn't do anything to sabotage their success. I may have come off like Frankenstein but really I'm just an owner of a pair of pet zebra who hopefully soon will find some owls to fill her new barn cage. I plan to breed them if I can find enough unrelated birds to begin with. But thats another post... :)

Thanks again.

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Post by Crystal » Tue Mar 14, 2006 8:22 pm

You are correct. And I didn't mean to imply that you seemed like someone who would inbreed your birds, just that it's always a good thing to avoid doing.

:)

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