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Lodi, California

The single-trait 2x2 Punnett square has been pretty helpful in modeling genetic outcomes of Squash x AG crosses. However, I don't believe a single-trait model of inheritance adequately describes what we see with the progeny of these crosses. For example, what people call "Squmpkins", squash plants that produce fruit with undesireable coloration.

In fact, it's rather uncommon for genetic traits to be coded by only a single gene. Many traits are polygenic, meaning controlled by more than one gene. This requires a larger punnett square to model, and results in a much larger variation of genetic outcomes. Here's a website that allows you to visualize these larger punnett squares:

https://scienceprimer.com/punnett-square-calculator

Now for some real examples to showcase this. Take the 1844 Holub. This world record was the result of crossing the 282 Scherber (1725 harp x self) with the world record 1578 Holub world record in 2014. Scott then isolated the green coloration in 2015 through selfing, and grew the world record in 2016.

The 1844 was a good seed that produced some big squash, and was relatively true to green. However, it did produce its share of squmpkins as well, which shouldn't have happened assuming a single trait was present, as modeled by a 2x2 punnett square. Instead, I think there was more than one gene in control of coloration. To oversimplify, the particular seed Scott grew to produce the 1844 (1060 Holub) wasn't the silver bullet seed with all genes coding for green, but it did mostly code for green. Assuming a 2 trait 4x4 punnett square, only 1/16 of the 1060 Holub seeds would have coded for pure green.

So what does that mean for us now? Squmpkins are not very common anymore now that we've selectively bred multiple generations of green offspring, and disregarded the squmpkins. However, I think this is good information to know when it comes to inheritence of the green trait in cucurbita maxima.

12/15/2022 3:59:43 PM