# Help understanding homozygous vs heterozygous



## Chiilaa (Aug 12, 2010)

Your post is a little confusing. Has he produced a dilute foal from a definitely non-diluted mare?


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## Yogiwick (Sep 30, 2013)

I do agree your post is a little confusing.
Assuming the stallion is black and the mare is buckskin the foal could be black, chestnut, bay, smoky black, buckskin, palomino. With or without pinto.

I started to type a response on genetics but it was getting complicated..
check this out:
www.aces.edu/pubs/docs/A/ANR-1420/ANR-1420.pdf


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## Tryst (Feb 8, 2012)

Agree - a bit confusing 

Homozygous means that they carry the same gene at both loci, heterozygous means they carry two different genes. Each parent passes a gene from one of the two loci, so when you have a homozygous horse because both genes are the same it is 100% known what will be passed. If they are heterozygous it is a 50/50 chance which one will be passed.

An example is a chestnut horse, as they are always ee, so if they are bred every foal they produce will have a copy of e gene passed to it. Black based horses may be EE or Ee, and the only way to know is through testing or if they have produced a red foal or have a red parent (remember all red bases are ee), but both EE and Ee look the same. If the horse is Ee then there is a 50% chance that the parent will pass on the E and 50% they will pass on the e.

Hope that helps explain homozygous vs heterozygous.


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## Yogiwick (Sep 30, 2013)

If you want a more detailed response can you tell us what color foals the stallion has had when bred to what colored mares and same with the mare.


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## littrella (Aug 28, 2010)

Sorry, about the confusing post. he foals seem to be a lighter shade of the color of the dam, but even if the dam is a solid color, the foal will have pinto markings. So as to the homoz vs hetero, understanding what is what as to he passed on his pinto coloring, but not his coat color


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## Tryst (Feb 8, 2012)

Well there are multiple genes to every color. The stallion is still passing on color genes even if the foal is not the same color as the stallion. He may be heterozygous or homozygous for tobiano. Even though one foal got the gene does not mean he is homozygous for it.

Can you post pictures of the foal and the mare? Foal coats are often lighter than adult coats until they shed out.

I still don't understand your questions. 

Perhaps the Color Calculator will help you figure it out --> Color Calculator


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## Chiilaa (Aug 12, 2010)

Without seeing his DNA report, there is no way to tell if he is homozygous for tobiano to be honest. If you want to use his foals as a way to tell, he would need to have sired 100 or more foals before you could be reasonably sure, and just one that doesn't have tobiano in that 100 means that he is heterozygous.


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## littrella (Aug 28, 2010)

2 of this years foals. Hope this helps


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## littrella (Aug 28, 2010)

so homozygous is dominant while heterozygous is recessive? this is where I get confused


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## Tryst (Feb 8, 2012)

Homozygous just means two of the same gene, which can be two dominant genes (example AA) OR two recessive genes (aa). Homozygous means one dominant and one recessive.


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## littrella (Aug 28, 2010)

Tryst said:


> Homozygous just means two of the same gene, which can be two dominant genes (example AA) OR two recessive genes (aa). Homozygous means one dominant and one recessive.


ok, I understand that now, thank you.

The buckskin mare in the first photos is a maden. We were taking guesses as to what colors we might get. then debating the pinto factor & discussing homoz vs hetero & a simple conversation got very confusing quickly. I knew the color experts on here would understand this far more than I ever could


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## LovesMyDunnBoy (Aug 11, 2011)

I know next to nothing about paint genetics, but I understand base coats and modifying genes fairly well.

There are only two base coats possible; homozygous black (EE), heterozygous black (Ee), or sorrel/chesnut (ee). You can only have a homozygous sorrel, because the gene for sorrel (e) is recessive. Therefore any copy of the dominant gene (E) will make the horse black. 

So assuming that stallion is black, he could be either homozygous black (EE) or heterozygous black (Ee). If he's homozygous, he won't produce a sorrel based foal, period. (so no red duns, no palominos, no red roans etc.) 
I'll attempt to do a punnet square here, but I can't guarantee that it'll turn out lol!

Let's say he's homozygous black and the mare is sorrel; (in parenthesis are the possible offspring
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Mare- e - e 

Stud- E (Ee) (Ee)

E (Ee) (Ee)

So this stud bred with this mare will produce a heterozygous black foal.

Here's a heterozygous black stud with a homozygous sorrel mare;
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Mare- e - e

Stud- E (Ee) (Ee)

e (ee) (ee)

There is a 50% chance of a red based foal and 50% chance of a heterozygous black based foal. 

Did that make any sense? Haha, it's nearly impossible to show you without a picture or drawing, but I tried!
_Posted via Mobile Device_


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## LovesMyDunnBoy (Aug 11, 2011)

It took out all my spaces 
_Posted via Mobile Device_


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## Yogiwick (Sep 30, 2013)

Do you know the mare's parents colors?

As far as pinto the only way to tell 100% is to test him. Those foal's don't tell us much since they got the color from the dam.


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## LovesMyDunnBoy (Aug 11, 2011)

Here's a pretty good document to read about genes;

http://www.google.com/url?q=http://...sQFjAA&usg=AFQjCNHQF6B7zZUg1cbdPAfOujYiDfv6lg
_Posted via Mobile Device_


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## Peppy Barrel Racing (Aug 16, 2011)

Tryst said:


> Homozygous just means two of the same gene, which can be two dominant genes (example AA) OR two recessive genes (aa). Homozygous means one dominant and one recessive.


Tryst made a typo :shock: HETEROZYGOUS means one dominant one recessive


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## JCnGrace (Apr 28, 2013)

Color genetics are more confusing when discussing homozygous vs heterozygous so lets use the pattern gene instead.

First off is the very basic that each foal inherits 2 sets of genes, one set from the sire and one set from the dam. Keep in mind that sire and dam each have 2 sets of their own so are capable of passing along a gene from either set.

Tobiano is a dominant gene but if the mare or sire is heterozygous for tobiano then approximately half the time you'll get a tobiano foal and half of the time a solid foal if the other parent is solid. If both parents are heterozygous for the tobiano gene then the percentage of a tobiano foal raises to like 75%. (I'm doing this from memory so may not be totally accurate in my percentages but just trying to give you the jist of how it works.) And that 75% breaks down into something like 50% heterozygous and 25% homozygous for the tobi gene. 

If the dam or sire is homozygous for the tobiano gene this means they inherited a tobi gene from their sire and a tobi gene from their dam. They will produce color 99.9% of the time and recent studies have shown that the .1% is still tobiano just not showing any white but will still throw the tobiano pattern onto their own offspring 50% of the time just like any other heterozygous tobi.


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## Chiilaa (Aug 12, 2010)

I just want to clarify something quickly.

Homozygous means there are only the same genes present, to translate it literally. So this means that there are two the same, AA, aa, EE, ee, ToTo, tt, OO, oo and so on.

Heterozygous means there are differing genes present. This does not necessarily mean that they are one dominant and one recessive - remember that several different loci (the places pairs of genes are found) have multiple dominant mutations. So looking at the agouti loci for example, there are several ways the horse can be homozygous (AA, aa, AtAt, A+A+) and more ways to be heterozygous (Aa, AAt, AA+, aAT, aA+, AtA+). Some of these combinations are two differing dominant genes.


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## LovesMyDunnBoy (Aug 11, 2011)

Without knowing if the sire and dam are homozygous or heterozygous and assuming the sire IS black and the dam IS buckskin here are the chances (about, without decimals)

35% buckskin
35% bay 
11% smokey black
11% black
3% palomino 
3% sorrel

That's considering that the parents can be either of these;
Sire- Eeaacc or EEaacc only
Dam- EeAaCc, EEAaCc, EeAACc or EeAACc

(A-agouti[bay]gene C-cream gene E- black)

If the mare is buckskin (assuming she isn't a dunskin [buckskin + dun] or anything) she has to have a dominant black gene (Ee or EE) the agouti gene (Aa or AA) and only one copy of the cream (Cc) (two copies would make her a double dilute/perlino) 

And assuming the sire is honestly black he has to have a dominant gene for black (Ee or EE) no agouti (aa) and no cream (cc) 

The two foal pictures you posted don't help much as far as figuring if the sire is homozygous black (EE) or heterozygous black (Ee) because neither of the foals look to be red based. A black foal is obviously black based and a bay foal is black based with at least one copy of the agouti gene (EeAa, EEAa, EeAA, or EEAA). And of course he could be brown (A+ I believe) but I didn't really account for that.

If you could tell us more information, such as other foal this sire has produced, the color of the sire's parents or the color of the dam's parents it would be very helpful In narrowing down the possible genotypes of the mare and stallion.

Anyone feel free to correct me, I'm new to genetics!
_Posted via Mobile Device_


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