[joseph]

I'd guess that bush habit is a recessive trait, because wild squash are vining. (It's harder to stabilize a dominant trait than a recessive.) I haven't paid close enough attention to estimate whether yellow skin is dominant or recessive.

There have been something like 8 genes identified that are directly involved in fruit color in pepo squash. So in the worst case scenario where they are all recessive and there are no common genes shared between the two parents the odds are 15 in a million of finding the right combination to get the same colors. Could be worse than that considering that we don't yet know all the genes that affect fruit color in squash. Could be much better if the two varieties share many of the same genes. Then there are the genes for productivity and vining habit and flavor to toss into the lottery.

I prefer selfing to back-crossing because I can let nature do the crossing and there is no work involved for me.

Also, with selfing I might find something close to the combination I'm looking for among the F2. If I do back-crossing then it takes a year longer.

It'd also be possible to do a back-cross in the F2 generation if the traits I'm looking for don't show up. Or to manually cross a few plants that have the traits that most resemble the end goal.