Help understanding homozygous vs heterozygous - Page 2

       The Horse Forum > Horse Breeds, Breeding, and Genetics > Horse Colors and Genetics

Help understanding homozygous vs heterozygous

This is a discussion on Help understanding homozygous vs heterozygous within the Horse Colors and Genetics forums, part of the Horse Breeds, Breeding, and Genetics category

Like Tree8Likes

LinkBack Thread Tools
    12-15-2013, 10:34 PM
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.
littrella likes this.
Sponsored Links
    12-15-2013, 10:41 PM
Originally Posted by Tryst    
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
    12-15-2013, 11:07 PM
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
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;
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
littrella likes this.
    12-15-2013, 11:08 PM
It took out all my spaces :(
Posted via Mobile Device
    12-15-2013, 11:14 PM
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.
    12-16-2013, 12:07 AM
Here's a pretty good document to read about genes;
Posted via Mobile Device
    12-16-2013, 12:32 AM
Originally Posted by Tryst    
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 HETEROZYGOUS means one dominant one recessive
Tryst and BreakableRider like this.
    12-16-2013, 01:18 AM
Green Broke
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.
littrella likes this.
    12-16-2013, 05:24 AM
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.
    12-16-2013, 08:17 AM
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

Quick Reply
Please help keep the Horse Forum enjoyable by reporting rude posts.

Register Now

In order to be able to post messages on the The Horse Forum forums, you must first register.

Already have a Horse Forum account?
Members are allowed only one account per person at the Horse Forum, so if you've made an account here in the past you'll need to continue using that account. Please do not create a new account or you may lose access to the Horse Forum. If you need help recovering your existing account, please Contact Us. We'll be glad to help!

New to the Horse Forum?
Please choose a username you will be satisfied with using for the duration of your membership at the Horse Forum. We do not change members' usernames upon request because that would make it difficult for everyone to keep track of who is who on the forum. For that reason, please do not incorporate your horse's name into your username so that you are not stuck with a username related to a horse you may no longer have some day, or use any other username you may no longer identify with or care for in the future.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Old Thread Warning
This thread is more than 90 days old. When a thread is this old, it is often better to start a new thread rather than post to it. However, If you feel you have something of value to add to this particular thread, you can do so by checking the box below before submitting your post.

Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
Homozygous question! MangoRoX87 Horse Colors and Genetics 24 07-13-2012 04:17 PM
Homozygous Grey vs Heterozygous Grey <PIC heavy> SunnyDraco Horse Colors and Genetics 27 03-12-2012 01:54 AM
Breeding to a Heterozygous stallion for 2013 MyLittlePonies Horse Breeding 19 07-26-2011 09:46 PM
Breeding a homozygous black/white to a homozygous red/dun? APHAforlife Horse Colors and Genetics 26 03-15-2011 08:58 PM
Grey horses... Homozygous and Heterozygous trends? Fiyaero Horse Colors and Genetics 16 02-13-2011 07:23 PM

All times are GMT -4. The time now is 02:26 PM.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0