Poultry genetics - Comb type

I am trying to get to grips with genetics. I have always known when breeding you only breed from the best and closest to 'type' as possible. Common sense really.

This year the Indian game cockerel threw a couple of single combed offspring - pea comb being the standard for the breed. Even though the Indian Game pullet has beautiful markings, is a good size and shape and has already come into lay, I won't breed her back to the cockerel. I am however intrigued at the genetic make up of the birds and in the likely percentage of this happening again.

As I understand it this is how it works.

Despite the diversity of comb shapes all types can be traced back to just two genes the Pea comb gene and the Rose comb gene, both of which are located on different chromosomes - each chromosome having two genes. Therefore each bird has a total of four genes, these determine its comb type, depending on the dominant gene (or lack of )

The genes can be represented by P (dominant) or p (recessive) for Pea comb and R (dominant) or r (recessive) for Rose comb.
If a dominant gene is present in the birds make up only one is needed for the trait (ie comb shape) to be expressed.

Working backwards we know a single comb type can only be produced by all recessive genes being present i.e the pullet must have the genetic make up for comb type of (pp) (rr)

The parents therefore have the genetic make up (Pp) (rr), both showing Pea comb because of the Dominant (P) gene but carrying mostly recessive genes. This will result in a 25% chance of the offspring having the single comb.

This can been shown as below using The Punnet Square.

Punnett Square Calculator - Two traits, Autosomal

Parents
Parent (top):	AA Aa aa
	BB Bb bb
Parent (left):	AA Aa aa
	BB Bb bb

Traits	CC	Cc	cc
Dominant A
Co-dominant A
Recessive A
Dominant B
Co-dominant B
Recessive B

Punnett Square
	Ab	Ab	ab	ab
Ab	AAbb	AAbb	Aabb	Aabb
Ab	AAbb	AAbb	Aabb	Aabb
ab	Aabb	Aabb	aabb	aabb
ab	Aabb	Aabb	aabb	aabb

Frequencies
AAbb	4
Aabb	8
aabb	4

If I were to breed the single comb pullet back to the father the chance of a single combed bird being produced would be 50%

All the young hatched this year with a pea comb,carry either the genes (PP) (rr) or (Pp) ( rr ).
If the birds with the genetic make up of (PP) (rr) were to be bred back to their father all the offspring would carry at least one dominant gene for Pea comb.

With careful selection over the next few years I should have a flock of birds that carry only the Dominant Pea comb gene.