25 November 2011

Aberrant Angela's Blue - musings on heterozygosity

I'm growing four or five plants of each of my purple podded parent lines, one of which is Angela's Blue. However, one of the plants seems to not be carrying its full complement of purple podded genes. As discussed elsewhere, I need A to turn on anthocyanin production, and Pu and Pur to express this colour in the pods. I've been wondering what would happen if I only got one of Pu or Pur as a result of one of my crosses. This aberrant plant of Angela's might indicate the result. It shows a dappled purple colouration.

A developing pod on Aberrant Angela's Blue
The plant has only two pods, so it might not be a good plant to choose as a pollen donor, but both pods show this patterning. So how might this have arisen?
A, Pu and Pur, the three genes needed for purple podding are dominant. Whoever bred Angela's would have had to select for purple podded phenotype from their original cross. This means the plants they selected from would have had to be carrying A, Pu and Pur. But you can't tell if the plant has one copy of the dominant gene (heterozygous) or double copies (homozygous) unless you grow out lots of the progeny. My guess is the original parent was heterzygous, was grown out for a number of generations until the breeder thought it was homozygous for all three genes, but lurking in the population from which the seed was collected was a plant which was heterozygous for either Pu or Pur.

This is what a purple podded is supossed to look like:

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