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All confused with Roan

JNFerrigno April 23, 2011 April 23, 2011

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Alright a few years ago I took an Intro to Biology class (I goofed and thought I was taking Bio), and in their genetics chapter they had the typical red, pink, and white flowers (hibiscus if I remember), peas, flys, ect. In the case of flowers, they were explaining a red flower was RR, a white flower was rr and a pink flower was Rr. I forgot the genetic term here, not incomplete dominate...ugh. Just took my test tonight on it to LOL wonder if I failed that question....any way. This chapter all those years ago, there was a Blue Roan horse, which represented a mixture of black and white. So that a RR horse would be Black, a rr horse would be white, and an Rr horse would be roan. I tried to get my professor to explain this to me after class, and it became heated, and I was told I was wrong and that I should go by the book. So moving on to my next class. My recent Biology class I am taking has used cattle as an example of Roaning. Which that works (to my understanding of roan in cattle). It's not symbolized as R for roan I believe. But if I remember correctly the RR red cow will be solid, a rr cow will be white, and a Rr cow will have a mixture of the two randomly on the body. Cattle Roan doesn't follow the same patterns we see in equine roan. So....just what the heck is the deal on roan?! (in horses)

Katie Sat, 04/23/2011 - 02:44

Roan is not an incomplete dominant. One copy means that the horse will display roan. So a heterozygous roan displays the same as a homozygous roan.

Your old professor was wrong. However, back then it was probably because of the theory that a homozygous roan would die in utero.

RiddleMeThis Sat, 04/23/2011 - 06:40

[quote=JNFerrigno] I forgot the genetic term here, not incomplete dominate...ugh. Just took my test tonight on it to LOL wonder if I failed that question....any way.[/quote] I believe the term you're looking for is "Co Dominant".

[quote]This chapter all those years ago, there was a Blue Roan horse, which represented a mixture of black and white. So that a RR horse would be Black, a rr horse would be white, and an Rr horse would be roan. I tried to get my professor to explain this to me after class, and it became heated, and I was told I was wrong and that I should go by the book. So moving on to my next class.[/quote] In cattle that is how it is. "rr" is non roan, RNrn is roaned, and RNRN is white, but that is not how it works in horses. In horses it is a simple dominant. "rr" is non roan, RNrn is roan, and RNRN is still roan.

[quote]My recent Biology class I am taking has used cattle as an example of Roaning. Which that works (to my understanding of roan in cattle). It's not symbolized as R for roan I believe. But if I remember correctly the RR red cow will be solid, a rr cow will be white, and a Rr cow will have a mixture of the two randomly on the body. Cattle Roan doesn't follow the same patterns we see in equine roan.

So....just what the heck is the deal on roan?! (in horses)[/quote]See above.

JNFerrigno Sat, 04/23/2011 - 09:10

Thanks, thats what I thought. I mean thats what I've always known. But then you have a text book and two professors against the idea and I start to wonder if I had it wrong all this time. LOL and I was thinking Co Dominate last night, but I wasn't sure if I was making up terms now LOL.

Threnody Sat, 04/23/2011 - 09:58

That's frustrating. Those books were very outdated.

There is a stigma with the white homozygous roan heifers since they are often infertile and less valuable to the cattle industry. This is known as white heifer disease. People would apply the knowledge of white heifer disease to horses (don't breed roan to roan). This contributed to the idea of lethal roan in horses.

I'm also wondering if the fact that roan x roan matings never produced white offspring may have contributed to the thought that homozygous roans are impossible and lethal.

Monsterpony Sat, 04/23/2011 - 12:29

Interesting theory on the lethal roan idea.

This is how I remember incomplete versus codominant from way back in high school biology-

Incomplete: Red + white = pink
This is because neither is strong enough to take a stand so they mix together

Codominant: Red + white = red and white stripes
Both genes are strong enough to fully express so they manage to fight for their own expression to show.