[Araucanas] Homozygous Ear Tuft Gene

Hello there! As you can see, I don't own any poultry yet as I'm working through the permits, space and everything, but I'm just wondering two things about homozygous ear tufts for Araucanas. What makes the gene lethal? Does it somehow affect organs? Why do the chicks mostly die if they have the EtEt combination? What kills them?

Oh, and:

Is it possible to hatch an EtEt individual?

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0040974
It's pretty detailed, and there is a lot of geneticist jargon to sift through, but it does help shed some light on the lethal tuft gene.

"These data indicate that Et is located in a region containing partial coding sequence for GNB1L, which encodes a protein implicated in neuropsychiatric disorders [24], [25], and complete coding sequence for TBX1[26], an important transcriptional regulator of embryonic development."

The lethality of the gene is due to where it is located on the genome. It's near a regulator for embryonic development. It's not necessarily the tuft gene itself, but it's proximity to other genes that is the problem.

Potoooooooo said:

Hello there! As you can see, I don't own any poultry yet as I'm working through the permits, space and everything, but I'm just wondering two things about homozygous ear tufts for Araucanas. What makes the gene lethal? Does it somehow affect organs? Why do the chicks mostly die if they have the EtEt combination? What kills them?

Oh, and:

Is it possible to hatch an EtEt individual?

Click to expand...

The gene is lethal because embryonic development is not properly regulated. You can see ear tufts on the outside but the damage is found on the inside of the bird.

In humans, the same dysfunctional gene TBX1 causes Digeorge syndrome. This gene is pleiotropic ( effects more than one area) and causes the incorrect development of the ear and the area around the inner ear and also the upper portion of the cardiovascular system. Similar effects are observed in mice and zebra fish.

Most likely the embryos die because of an anomalously formed ear, throat, cardiovascular system and gland found in the neck and head region. The chicks death is due to what is referred to in genetics as haploinsufficiency. The chick's cells that carry one good allele and one mutated allele take part in a process that makes a properly working product (the good allele) and the mutated allele which is responsible for making a bad product that causes the malformations. The chicks cells do not make enough good product that would cause normal development.

Embryos that are ET*ET/ET*et usually die between day 20 and 21; about 40% of the embryos die. Some additional chicks will die after hatching.

Birds (homozygous) that carry two copies of the dysfunctional TBX1 ( tbox 1 protein) allele or ET allele very seldom develop past 19 days and if they do hatch die after they hatch. Some homozygous birds do live to maturity and are able to reproduce but this is rare.

I read that experiment... it’s very interesting... but I have a question - is the tuft gene dominant. For instance if a bird only had one copy of the gene would they still get muffs?