Help understanding homozygous vs heterozygous - The Horse Forum
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post #1 of 20 Old 12-15-2013, 09:01 PM Thread Starter
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Help understanding homozygous vs heterozygous

Every time I think I understand this, I don't. Can someone please dumb it down so I can understand what each term mean?

My friends that breed mini's & I are trying to figure out what color 1 of their 2014 babies might be. They are trying to find the color report that came with their stallion, but right now, it's misplaced. The past 2 breeding seasons he has produced a diluted color of the dam but usually with the pinto pattern. So if we are crossing him with this buckskin mare, we could get????
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Last edited by littrella; 12-15-2013 at 09:02 PM. Reason: typo
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post #2 of 20 Old 12-15-2013, 09:49 PM
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Your post is a little confusing. Has he produced a dilute foal from a definitely non-diluted mare?

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post #3 of 20 Old 12-15-2013, 09:53 PM
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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

Last edited by Yogiwick; 12-15-2013 at 10:00 PM.
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post #4 of 20 Old 12-15-2013, 09:57 PM
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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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post #5 of 20 Old 12-15-2013, 10:03 PM
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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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post #6 of 20 Old 12-15-2013, 10:04 PM Thread Starter
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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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post #7 of 20 Old 12-15-2013, 10:23 PM
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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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post #8 of 20 Old 12-15-2013, 10:23 PM
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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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post #9 of 20 Old 12-15-2013, 10:24 PM Thread Starter
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2 of this years foals. Hope this helps
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post #10 of 20 Old 12-15-2013, 10:26 PM Thread Starter
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so homozygous is dominant while heterozygous is recessive? this is where I get confused

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