Learning Genetics

I have been reading the genetics guide - Please explain in laymen’s terms about 

EE aa black, Ee aa black carrying red.

I have a white chinco foundy whose full genetics are underneath.  I realise that the little letters mean he does not have the trait but can pass on some of them to progeny but I do not understand the first bit.

Ee aa gg crcr dd chch FF zz pp stysty rbrb W+ oo spsp lplp patn1patn1 patn2patn2 - furtive follower in the myst.

After the capital E (presumably from the sire) can the underscore mean a little e or another capital from the mare ?    E_ AtAt brown

I don't have time to write out a long explanation now, but playing around with this can help! 

From my knowledge (please correct me if I'm wrong) anytime the horse with E_AtAt passes on the E (extension gene) to foals, they'll also pass on the AtAt (brown) gene.

E_ means E-and-whatever. It means it can be Ee or EE. A horse with Ee AtAt will pass on EITHER E or e, but will pass on At every time because it is homozygous. Punnett squares can help you determine possible genetics of foals. 


Edit: Okay, my kids are asleep, I can explain in detail:

ee aa, ee Aa, ee AA - Red (chestnut); the As don't matter here because Agouti only acts on black, E.

Ee aa or EE aa - Black; E allows black pigment to enter the hair shaft 

Ee Aa, EE Aa, Ee AA, EE AA - Bay; E allows black pigment, then A pushes that black pigment to the extremities of the horse, creating Bay (red with black points)

These are the only thee base coat colors. All other "coat colors" (like Cremello, Palomino, etc) are just modifications (dilutions, like Cr. Ch, D or Prl in real life) of these 3. 

Example:
Let's say you have a Bay horse with Ee Aa and a Chestnut horse with ee aa.

For these Punnett squares, Bay is horizontal, Chestnut is vertical.

      E.       e.                    A.        a. 

e.   Ee.   ee.             a.    Aa.     aa

e.   Ee.   ee.             a.    Aa.     aa

So, there is a 50/50 chance of Ee and ee; same for Aa and aa.

In this square I am finding the probability of combinations. Agouti is horizontal, Extension is vertical. 

.       Aa              aa                

Ee   Ee Aa.     Ee aa          
        Bay.        Black
ee   ee Aa.      ee aa       
         Red.         Red


So, from my hypothetical pair, you have a 50% chance of red, a 25% chance of black (remember that E allows black pigment to enter hair shaft) and a 25% chance of bay (remeber A along with a E pushes black pigment to points).

Theoretically, if that pair had 4 foals, 2 would be red, 1 would be bay, and 1 would be black - but of course, theoretical probability (what should happen based on numbers) is different than experimental probaility (what really happens in real life with chance involved). 

Whew! 

Hope that helped!

(Please excuse any typos-  typed this on my phone, in bed, after a day of raising 2 toddlers who got up at 6am!)

Last edited on 2018-01-22 at 22:16:21 by North

There is a helpful guide to all genetics here. :)

She said she had been reading the Genetics Guide but still needed help in layman's terms. ;)