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Tuft Genes and Araucana Hatchability

By Richard Collard
Edited by Alan Stanford, Ph.D.

The tuft gene is a dominant autosomal gene and is lethal when an offspring has two copies of the gene (is pure for the gene); it will kill the embryo before it hatches.

On this web site
The tuft gene is represented by the symbol	Et
The no tuft gene is represented by the symbol	nl

Research has shown that almost all embroyos homozygous for the tuft gene die after 17-19 days of incubation. A few might hatch, but most die within a week. Occasionally an "escaper" lives to maturity. One such Araucana has been verified. These rare birds do not transmit their viability to their offspring. Heterozygotes (birds heterozygous in the gene) also experience increased embryonic mortality at about 20 or 21 days of incubation.

Tufts are difficult to perfect for showing. They can grow in many different ways, sizes, and shapes.

Tufts can grow on both side of the head or on only one side.
They can be very big or very small.
They can be just a fleshy peduncle with no feathers.
They can be different sizes on different sides of the bird or the same size on both sides.
They arise near the ear, on the throat, or even internally.
They can be upswept, spiral, tear drop, or other shapes.
There can be a different shape on each side of the head.
Rare birds have more than one tuft on the same side.

That's why a breeder is happy if she hatches a few chicks a year with big even tufts .

Table of hatchability
(Et,nl) x (nl,nl) Tufted (heterozygous) x Not tufted (homozygous)
(Et,nl) Tufted (heterozygous)	50% of Eggs	44% of Survivors	20% die before hatching Some survivors have no visble tufts
(nl,nl) Not tufted (homozygous)	50% of Eggs	56% of Survivors	All live and vigorous

Table of hatchability
(Et,nl) x (Et,nl) Tufted (heterozygous) x Tufted (heterozygous)
(Et,Et) Tufted (homozygous)	25% of Eggs	None of Survivors	Rare Survivors
(Et,nl) Tufted (heterozygous)	50% of Eggs	62% of Survivors	20% die before hatching Some survivors have no visble tufts
(nl,nl) Not tufted (homozygous)	25% of Eggs	38% of Survivors	All live and vigorous

Glossary

Autosomal	This gene is independant of sex; it affects both sexes equally.
Sex linked	This gene has a different effect on different sexes.
Dominant	An organism (plant/animal) with a single copy of this gene shows the effects of this gene.
Recessive	This gene has is not evident unless the organism (animal/plant) has two copies of this gene.
Homozygous	The organism has two copies of this gene.
Heterozygous	The organism has only one copy of this gene. The matching gene is different.

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