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NEMO | This post is derived from a thread below and is meant to be informative and has to do with Homozygous and Heterozygous. We still get lots of questions concerning it, so I feel like many people do not understand it. I will try to explain it in simple terms, and hope I don't make many mistakes, and if I'm missing something or wrong, I'm sure someone will point it out.
Hair coat color is determined by 'alleles' and every animal has two 'alleles'. One 'allele' comes from the father and one 'allele' comes from the mother.
Usually the 'allele' for hair coat color is represented by either a big 'B' which is Black, or a little 'b' which is Red.
Black (B) is dominant over Red (b) recessive.
HOMOZYGOUS means 'two' of the same allele. (I.E. Homosexual for lack of a better example)
HETEROZYGOUS means one of each different allele. (I.E. Heterosexual)
A cow or bull that is black in color is going to be either HOMOZYGOUS Black 'BB' (two big B's that are dominant) or HETEROZYGOUS Black 'Bb' (one big B and one little b). The Heterozygous black animal is genetically half Black and half Red, but since Black is dominant you see a 'Black' animal.
A cow or bull that is red in color is only going to be HOMOZYGOUS RED 'bb' (two little b's that are recessive). No Red animal can be carrying a 'black' gene, becuase if it was then the animal would have came out black since black is dominant.
If you mate a HOMOZYGOUS Black 'BB' bull to a Homozygous Red 'bb' cow, you will always get a black calf since the Homozygous Black bull is passing on one of it's big 'B's to the calf while the Red cow is passing on one of it's little 'b's to the calf. The calf is Heterozygous Black 'Bb'.
If you mate a Heterozygous Black 'Bb' bull to a Heterozygous Black 'Bb' cow 4 different times you will get 3 Black calves and 1 Red calf.
1 of the Black calves will be Homozygous Black 'BB' because the calf got a big 'B' from the bull and a big 'B' from the cow.
1 of the Black calves will be Heterozygous Black 'Bb' because it got a big 'B' from the bull and a little 'b' from the cow.
1 of the Black calves will be Heterozygous Black 'Bb' because it got a little 'b' from the bull and a big 'B' form the cow.
The 1 red calf 'bb' got a little 'b' from the bull and a little 'b' from the cow.
Hopefully the 'science' from this post will help to answer one, or some, of the questions from the previos thread. A heterozygous Black Hereford bull bred to a heterozygous Black Hereford cow will produce a Homozygous Black Hereford animal 25% of the time. The resulting Homozygous Black Hereford animal will always produce a black calf. The same 'science' can be applied to Black Simmental, Black Gelbvieh, Black Saler, etc.
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Homozygous and Heterozygous Hair Coat
