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Colorado

I have heard a few people say that if I take a (squash x pumpkin) cross, and then cross it back with a squash the following year, that it is likely that 50% of the progeny of that new seed stock will be green.

Can someone please explain the genetics/math behind that?

Also, if I took a (squash x pumpkin) cross, and then crossed it with a different (squash x pumpkin) cross the following year... can we logically say what % of the new progengy from this new seed stock would be green?

thanks.

3/4/2011 1:15:33 AM

Corryton, TN

All the following is assuming the green gene is a single recessive gene. I'll use P for pumpkin colors (shades of orange) and s for squash colors (shades of green).
Each fruit has a pair of genes that control the color of the fruit. In most of today pumpkins the genetic code would be PP and we get pumpkins. Likewise squash will be ss and we get a greenie. If we cross the two plants either way the resulting offsring will all have a code of Ps. Each P can combine with either s. There are 4 possible Ps combinations and since the orange is the dominate color, all the fruit produced by these crossed seeds will be orange.

If we use a crossed seed (Ps) and cross a squash (ss) onto it the 4 possible resulting are Ps Ps ss ss. 2 pumpkins, 2 squash.

Crossed seed (Ps) onto a crossed seed (Ps) results are PP Ps Ps ss. 3 pumpkins 1 squash

3/4/2011 7:25:01 AM

Somerset,Ky

Pete don't go pass the F-1 1/2 pumpkin crosses

3/4/2011 7:41:19 AM

Picton,ON (j.vincent@xplornet.ca)

Dave...that was an excellent explanation and easy to understand.

Just to through a fly in your ointment, if you self a Ps cross, you usually get 50% squash, and if you self that generation, you will usually get 75% squash. In your explanation you said a Ps x Ps should result in 100% orange, but there must be something different happening when selfing.I don't think the same thing happens when sibbing

3/4/2011 12:23:28 PM

Germany

I think Dave is right : According to Mendelian Laws all plants of the cross Pumpkin / Squash should throw pumkins, And if you pollinate such an F1 pumpkin/squash-cross with another F1 ( no matter if selfed,sibbed or a completly unrelated F1 cross the resulting seeds should throw pumpkins and squashes in relation 3 : 1.
But this math only works when the pumpkin in the cross is a "purebred" pumpkin ( PP). If P is the dominant gene for pumpkin colour, the pumpkin could have Ps in its genes. In that case the cross Squash x Pumpkin would be ss x Ps. And like Dave wrote, should result in 50% squash,50% Pumpkin. And that would fit with Johns post. Before my brain starts smoking, some field data . In 2009 I got 2 greenies out 5 of my 905 (selfed F1 cross ) and in 2010 1 greenie out of two . The 905 has alot of 845 Bobier in it and I think there are some hidden squash genes in it. This year I also tried a selfed seed out of a 848* x 1420 and only 1 squash out of 8 plants. So the genetic background of the pumpkin has a big influence. ( And another topic : probably the colour is not only determined by one gene )

3/4/2011 6:48:37 PM

Corryton, TN

That's why I posted "All the following is assuming the green gene is a single recessive gene."

What I should have said is if you cross a PP and ss the results (Ps) should be 100% orange.

None of this takes into account that I hypothesize that there is at least 1 other gene that controls white, blotching, ticking etc. If it or they are there it's possible they could be dominate and/or recessive. Or possibly work in an on/off fashion. So many possibilities, so few answers.

I wish we could plant 100's of the selfed and sibbed (Ps)'s to see where the stats fall. It might lead to more questions than answers.

3/4/2011 6:55:17 PM