Punnett Square

I posted this in response to a question in another thread, but I figured I'm sure a lot of people dont really understand how to set up a punnett square, so I'm just going to copy and paste from my other thread.

It's really not that bad, unless you've got a lot of hets--and then it just gets drawn out and you're more prone to making errors when you have to foil.

Say you've got a corn snake that's caramel het for amel and motley (butter mot).

That particular snake can give off the following possible combos, which is what you use for the punnett squares.

The makeup of the snake is this: ccAaMm

To be butter, the snake would obviously have to be: ccaa, and to be butter motley it would need to be: ccaamm

So, the possible combos from ccAaMm would be:

When you've got a recessive expressed trait, it can obvously only give off that expressed trait, so you know you'll only have the snake passing along the "c", in this case.

cAM
cAm
caM
cam

If you mated this hypothetical snake to one of the same genetic makeup, your punnett square would look something like this.


-----------cAM------cAm------caM------cam

cAM-----ccAAMM--ccAAMm--ccAaMM--ccAaMm
cAm-----ccAAMm--ccAAmm--ccAaMm--ccAamm
caM-----ccAaMM--ccAaMm--ccAaMM--ccAaMm
cam-----ccAaMm--ccAamm--ccaaMm--ccaamm


There's your punnett square.

Anything with two capital letters is going to be normal, there will be no trait expressed or not expressed, it's just not there. For example, MM is nothing, just normal. So the line ccAaMM would give you caramel het butter (amel), and there wouldn't be any motley in there.

ccAAMM= caramel, ccAAMm=caramel het motley, ccAaMM= caramel het butter, ccAaMm=caramel het butter motley, ccAAMm=caramel het motley, ccAAmm=caramel motley, etc etc.

The hardest part about the whole thing is accurately getting the possible combos thrown by each parent. When you start getting into more than a few hets it gets confusing.

I just wanted to add that you can always double check yourself with the predictor.

Using what I posted for traits, you'd come up with this:

Male is, Caramel, Het for Amel, Het for Motley
Female is, Caramel, Het for Amel, Het for Motley

Offspring are predicted to be...
25.00%, Caramel, Het for Amel, Het for Motley
12.50%, Caramel, Motley, Het for Amel
12.50%, Butter, Het for Motley
12.50%, Caramel, Het for Motley
12.50%, Caramel, Het for Amel
6.25%, Butter, Motley
6.25%, Caramel, Motley
6.25%, Butter
6.25%, Caramel


6.25% is 1/16, and if you look above out of 16 possible babies, the probability of getting a butter motley is 1/16, or 6.25%. This is for genotypes, if you want to just see what the snake will look like, or the expressed genes, you want to be looking at the phenotype.

When you finish your punnett square, there's a shortcut for this.

Make sure when you add things up, you go with the dominant letter first, as in Mm, not mM. There is a reason for the madness.

If you just want to see what your snake will look like, just go through and cross off the second letter of each trait.

For the ccaamm line, you would end up with:cam= butter motley.

For the ccAaMM line, it would be cAM= caramel (het for amel, it just is a hidden trait, and not expressed)

This works for all of them, if you're interested in a phenotype report instead of knowing all of the hets, or in case you want both.


Punnett squares themselves are not that difficult, the main problem is correctly coming up with the combonations or possibilities that each snake can give off.

Just remember when you're doing that, like for our example (ccAaMm) each heterozygous trait equals 2, homozygous equals 1. You're probably thinking, what in the hell, but watch.

cc=1, Aa=2, Mm=2

2x2= 4

How many possibile combos can that caramel het butter motley give? Answer is 4. That's a great way to check yourself when you come up with your combos.

Say you've got a caramel het hypo, motley, amel.

ccHhMmAa

Hh=2, Mm=2, Aa=2, 3x2= 6, so you'll end up with 6 possibile combos.

Not that bad once you work these out a few times.

Hope that all helps!

So it's not rocket science after all?!

Thanks for posting that. I've never even tried to understand breeding and genetics. I'm just getting started as a corn snake owner and only own 2. But you just got me interested. You've explained it well. Now I'm off to read up some more on it all.

Joejr14 said:

Say you've got a caramel het hypo, motley, amel.

ccHhMmAa

Hh=2, Mm=2, Aa=2, 3x2= 6, so you'll end up with 6 possibile combos.

Click to expand...

Small correction, it's 2 X 2 X 2 (2³, not 2*3) which is 8 possible combos.

The number of possible gametes (sperm/egg) is always a power of two. (1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, etc.)

(You can "count" your way through the gametes to figure them all out, but it becomes more work than it's worth. This is the nice thing about my "shortcuts" that I teach in the morph guide... they eliminate the excess grunt work. )

Serpwidgets said:

Small correction, it's 2 X 2 X 2 (two to the third power, not two times three) which is 8 possible combos.

The number of possible gametes (sperm/egg) is always a power of two. (1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, etc.)

(You can "count" your way through the gametes to figure them all out, but it becomes more work than it's worth. This is the nice thing about my "shortcuts" that I teach in the morph guide... they eliminate the excess grunt work. )

Click to expand...

Whoops!! LOL. I figured I'd make a mistake in there somewhere. Thanks for correcting that. And for some strange reason I cant edit my original post, so oh well.

*eyes swirl*

I remember doing this with black and white guinea pigs...

That's awesome though. Breeding corns seems like a fun thing to do. It's kind of like a grab bag. Throw this corn in and this one and out pops these ones!!

HadesBP18 said:

*eyes swirl*

I remember doing this with black and white guinea pigs...

That's awesome though. Breeding corns seems like a fun thing to do. It's kind of like a grab bag. Throw this corn in and this one and out pops these ones!!

Click to expand...

Absolutely. That's the whole fun of it. Get a snake that's a triple homozygous and mate it with one that's het for some of those, and wheeew. You can wind up with clutches that have quite the variety.