View Full Version : HOMOZYGOUS

12-04-04, 11:38 AM
To get a homozygous pinto would you have to have two coloured parents to produce colour every time.

12-04-04, 04:18 PM
only a homozygous Pinto produces 100% Pintos.
If you breed two heterozygous Pintos together you get:
50% heterozygous Pinto
25% homozygous Pinto
25% solid color

If you breed a heterozygous and a homozygous Pinto together you get:
50% heterozygous Pinto
50% homozygous Pinto

Hope that makes it clear.

12-04-04, 11:28 PM
What is a heterozygous? and how do you get a homozygous pinto because to get a homozygous grey all you have to do is cross two greys and if the foal is grey it is a homozygous that will throw grey every time.

13-04-04, 01:42 AM
So if a homozygous tobiano is put to a bay or chestnut mare, is the resultant progeny 100% black and white, or can it be brown and white? Does the homozygous status simply mean the offspring will be coloured in that it will be white and some other solid colour, but not necessarily black like the stallion? Just interested as I overheard someone talking about looking for a mare who MUST be black because she wants to breed a tobiano, using a homozygous tobiano stallion.

13-04-04, 07:28 AM
that is not correct. Each grey is born with a color and is greying out with time, no grey is born grey. Grey is no color it is a gene that modifies the color to grey with age. If you breed a grey mare to a grey stallion and they are both heterozygous you get:
50% greying out horses that are heterozygous (means giving the grey gene on to the foal only at 50%, 50% will be normal without grey gene)
25% of this mating will be homozygous for grey (means passing on the grey gene at 100% to each foal)
25% of this mating will be of normal color (means bay, chestnut, black etc.)

Tobiano is a pattern not a color, so if a horse is homozygous for Tobiano it gives the PATTERN at 100% to the offspring, not the color.
The stallion Sempatico I had before selling to the USA, was a homozygous Tobiano in black and white. His foals have been 100% Tobiano (Pinto) but came in bay and white and black and white. He might also be homozygous for black, but we had not tested him for this. This would mean he would never sire a chestnut foal. With the agouti gene available it modifies the black to bay. The base colors are only chestnut and black. Bay is not a base color it is a black horse with the agouti gene modifier to make the horse bay.

13-04-04, 07:42 AM
Homozygous means that the horse carries 2 copies of the same gene. That means that it has inherited the same gene for that trait from each parent.

Heterozygous means that the 2 genes inherited from the parents for any trait are different and the dominant gene has expressed itself in the phenotype (appearance) of the animal.

Eg: grey is a dominant gene so any horse that is grey MUST have a grey gene. It may have inherited one (heterozygous) or two (homozygous) depending on the colour of the parents, but it must have at least one grey parent. If you breed from 2 grey parents there are a number of outcomes depending on the genetic makeup of those 2 horses. A homozygous grey horse (2 grey genes) will always have grey offspring, no matter what color the other parent, because it will ALWAYS pass on 1 grey gene (which is dominant). Homozygous animals for any trait (including for the grey color) are far less common than those that are heterozygous for that trait.
2 heterozygous grey parents (1 grey and 1 other color gene each) will have offspring that are:
25% homozygous (2 grey genes) grey that will go grey
50% heterozygous (1 grey gene and another color) grey
that will go grey as grey is dominant
25% other color (no grey inherited) where the color is
determined by the recessive, not expressed genes inherited.
1 homozygous grey (2 grey genes) parent and 1 heterozygous grey (1 grey and 1 other colour gene) parent will have 100% grey offspring. Of these 50% will be homozygous and 50% will be heterozygous.

Chestnut on the other hand is a recessive gene and will only be expressed if inherited from both parents so that the offspring is homozygous to chestnut. That is why 2 bay parents can have a chestnut offspring. Both parents in that case are heterozygous for both bay and chestnut. 25% off the time they would have a chestnut foal.

I do not know any thing about the dominance or otherwise of the colored genes. There are other breeders on this forum who are far more knowledgable than me but the above is a general application.
All this applies to every gene for every trait inherited so it is easy to see why it is so difficult to breed the perfect horse!!!

I do hope all that makes some sort of sense :)

18-04-04, 10:17 AM
I use to own a Pinto Stallion. We bred him from a Homozygous B & W Pinto to a Bay TB mare and got a Chestnut & White Tobiano. He himself produced 4 foals, all tobiano. This could of been just coincedence as technically he had a 2 in 4 chance of throwing colour. There is a good book called 'Horse Colours Explained' by Jeanette Gower. It is a easy book read and quite interesting.

In relation to throwing colour he threw 2 Black & White from bay mare, Chestnut & white from Chestnut mare and a tri- colour bay, black,chestnut & white from bay mare.

His sire in the 10yrs he was serving did not influence the colour only the pattern and the foals tended to lean towards the mares colouring.

It is really interesting when you get into it. I am not breeding coloured horses anymore but it is still interest even for the solid colours. We now have a black warmblood stallion who in the past has throw black or bay foals. Last year we got a chestnut from a blk/bay mare. Anyway I could go on forever.