25 April 2012

Purple snows, homo and heterozygosity and seed sources.

All the written material says purple pod colour is determined by 3 dominant genes, A,Pu, and Pur - so I'm trying to figure out what is going on in my purple podded snow pea crosses.
I grew 4 different purple poddeds last spring, and crossed them to a range of snaps and snows, some of which carried the A (anthocyanin) gene - they had purple leaf axils, and purple flowers.

Of the purples, two (at least) were indistinguishable, although from different seed companies - Lost Seed Co, and Select Organics. The F1s from all these crosses should all have purple pods, if the parents were homozygous. Not so. One of the F1s has big green snow peas developing. I figure that was one of my hangover crosses, and in the tangle of stems and shiraz induced fog, I've accidentally crossed two green snows by mistake. Ah well. But of the proper purple crosses, one of the F1s bears lovely deep purple pods, but the others are dappled purple.
My guess is the deep purples from the Lost Seed Co cross, were homozygous for A, Pu, and Pur. But somehow, the Select Organic parents weren't homozygous either for Pu or Pur, the two genes for expressing purple colour in pods. I grew 6 plants each of each purple parent, so would have expected at least one of the parents to show dappled pods if they had been heterozygous. (This happened with one of the six Angela's Blue, which exhibited just such a trait).

I'm not sure if I used the same parent plant for each of the SO crosses, but both of the SO crosses are exhibiting this dappled purple trait.
I could grow out the original seed again, but rogues wouldn't necessarily show up - if they are heterozygous, they will still be deep purple even if a non-purple recessive was lurking in there. A smarter move would be to grow out the (uncrossed) seeds I collected from these parent plants to see if they segregate for deep and mottled purple. That would be a clincher. Will have to see if I have room - I'm rapidly running out of garden beds, with all these growouts, and hundreds of F2s potentially to be grown next spring.

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