Double Splits in Zebra Finches -- CFW and Fawn

[MiaCarter]

Okay, so, I was very perplexed when my zebra pair had a fawn baby, Cecily:



The mum Juliette is a normal grey hen.

The dad Piper is a normal grey male, split to CFW (I'm positive. I bred him.)

I was perplexed when I got a little fawn hen from this pair!

The only answer was that dad Piper had to be split for BOTH CFW and Fawn. But I wasn't sure if this was possible. Both of these are sex-linked genes and I (erroneously) thought that those traits shared the same gene location (this is the case for CFW and Lightback, so you're either/or, not both.)

It was very confusing.

I researched here on the forum and beyond, but I couldn't find an answer.

So I emailed finch god Roy Beckham (eFinch.com).

The answer: A zebra finch male CAN have a double split to CFW --AND-- Fawn.

According to Roy, he can only produce fawn and CFW hens. He cannot produce grey hens. So any greys from this pairing are necessarily male (which is what I suspected anyways.)

Females cannot be split for a sex-linked genetic trait because they only have one Z gene.

(Males are homozygous, ZZ. Females are heterozygous, so they're ZW. So they carry a sex-linked genetic trait on the Z, the W doesn't carry any sex-linked genetic traits.)

So my male Piper is necessarily a NG split to Fawn and CFW. (As is his dad, Molly Sue.)

Mystery solved!

[delray]

MiaCarter we actually learned the ZZ and ZW genetics in birds. Very complicated stuff! Roy is following the finchforum account on Instagram. He's awesome.

[MiaCarter]

delray - Yes! Genetics are complex.

But it's fun when you have something to apply that knowledge to, like your own birds!

Birds can be especially confusing because they're the opposite of humans (where males are heterozygous XY and females are homozygous XX. Birds are the opposite. Males are ZZ and females are ZW.)

Genetics was something that always just "made sense" to me and it's come in handy! I especially love punnet squares. They're handy for figuring it all out for a particular pair.

[delray]

MiaCarter we also did those last year in science. Yes, it does come in handy, I would like to learn Gouldian genetics one day.

[lnlovesorange]

MiaCarter Sounds like this might be my case as well, or close to it...maybe my Melvin is only split to fawn though, not CFW & fawn, because I didn't get any "white' babies... But that should mean that my 2 grays are males, and my two fawns are females right? Or is mine a little different because he is ONLY split to Fawn.

[MiaCarter]

lnlovesorange -- Your Melvin could certainly have a double split.

He's definitely split to Fawn.
If he ultimately produces a CFW baby, you'll know that he has a double split to Fawn and CFW.

What's funny in my case is that Piper's dad, Molly Sue, is also necessarily split to CFW and Fawn.

Molly Sue has fathered babies, but we've never gotten a fawn so we didn't realize he had that split.

What's funny is I adopted Molly Sue from a friend who had a bunch of babies --- 2 or 3 clutches. But I don't remember anything but normal greys and CFWs. (I would have scooped a non-NG or non-CFW)
But I know she had already given some away. And perhaps the splits could have been passed along from NG to NG, as Molly Sue did to Piper.

[Aspen]

The same is true of fawn and lightback. My NG male is probably split to both. Fawn for sure, still checking out the LB.

[MiaCarter]

Aspen - Ah, you're right! It could certainly be a fawn/lightback double split.

I know the only one of the sex-linked genes you can't have a double split for is CFW and lightback because they occupy the same location on the gene, so it's either/or, not both.

And you could also have them split for something else like pied (So my Piper and Molly Sue actually have three splits -- fawn, CFW and pied.)

[Aspen]

But pied isn't a sex-linked split. The male I have is split for fawn and LB (probably), the two sex linked genes, but also for BB, OB and Isabel - yet he looks NG! His fawn female mate is also split for BB, OB and Isabel. Lots of interesting colors out of that pair, when you get all the combinations going!