Gouldians genetics, a briefing on dilutes?

[Meagan83]

Can someone please answer this question.

"Hi Megan

I have a favor to ask could you would explain to me why only males are dilute? I have myself in a bit of a mess haha"

This comes from a friend of mine. I cannot think of the best way to explain it to make it easy to understand. I know that the males carry two genes, so if they have a green+yellow it makes them dilute or SF yellow. Do hens only carry or show one gene for color? this always confuses me because I know they can be split...

[debbie276]

From the Finch Information Center genetic pages
http://www.finchinfo.com/genetics/lady_ ... colors.php

Dilute is the phenomenon of combining a 'yellow' Z (sex-linked) chromosome with a 'green' Z (sex-linked) chromosome in a purple-breasted bird. (Obviously since two Z chromosomes are required for this to occur, dilute birds can only be cocks.) Hens can never be dilute. The single yellow body gene "battles" with the green body gene for expression, and so a little of each gene is expressed making the bird not green nor yellow but a shade in between. This is the hallmark of incomplete dominance. Dilute will never occur in a white breasted cock (since then the bird who is SFYB will appear yellow), but dilute birds can be split for white breasted. Because the yellow gene suppresses the expression of black coloration and because the green gene mutes the effects of the yellow gene, any normally black area on the bird will appear grey (as opposed to white), so black headed birds will have grey heads.

[Meagan83]

Thanks, appearently my friend was elected to speak in a middle school biology class about homozygous, heterozygous, dominant, and recessive genes. She's using her Gouldians to explain these things, but realized she was less educated than she expected.

[Jasmin]

[quote="debbie276"]From the Finch Information Center genetic pages
http://www.finchinfo.com/genetics/lady_ ... colors.php quote]

Thanks for posting this article!
I was looking for a simple clean explanation and this article did it!
no science background needed

[debbie276]

The link for head, breast and body color genetics for gouldians is here:
http://www.finchinfo.com/genetics/lady_ ... /index.php

[nixity]

Thanks, appearently my friend was elected to speak in a middle school biology class about homozygous, heterozygous, dominant, and recessive genes. She's using her Gouldians to explain these things, but realized she was less educated than she expected.

The Pastel (aka Yellow) gene would be an example she could use as a co-dominant gene.
This is why Dilutes are Dilutes.. because the gene is neither dominant nor recessive, but co-dominant to the genes responsible for the normal body color (it is not simply a "green" body gene, but multiple genes that determine pigment deposition and structural colors that result in the green body color we see).
So, when a single copy is present in a male, it is like taking red paint and mixing it with white paint - you aren't left with pure red or pure white, but pink instead.

With the Pastel gene when a single copy on a male bird you get that same concept only think of it as taking a can of green paint and dumping about 50% more yellow into it, making the color more of a lime-green color.

The actual color depending on the bird and how much the melanins etc are suppressed by that pastel gene.

Females have full suppression because they can only inherit a single copy by default and that single copy interferes entirely with the expression of melanin pigment (which is related to structural blue color).

[Meagan83]

One thing confuses me. Females only have one gene for color but can be split for blue? Is this no different than being split for different breast color/ head color? And why can they be split for blue, but not split for yellow? These are my questions, not my friends, although I'm not sure she understands it either.
I know that blue is the only body color a bird can be split for . But the reasoning behind it piques my interest.

[nixity]

It is because blue body, along with breast color and orange head color, is an autosomal trait.
Yellow body (the pastel gene) and the red and black head color (really, a single gene that has two alleles, dominant is red, recessive is black) are sex linked genes wjich mean they 'live' on the Z chromosome.
Since females by default only have one (they are ZW), they can only inherit a single copy and express fully whatever they inherit in terms of being RH, BH or yellow body.

[Meagan83]

Thanks Tiff

[nixity]

Any time