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Old April 5, 2018   #40
bower
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Join Date: Feb 2012
Location: Newfoundland, Canada
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The nice thing about Beta is that you can see if it's there, even in F1 or any heterozygous generation. The standard ratios apply to the color, so you would expect one in four to be BB in the F2, and two of four to be B/- visible as orange-red.
So you can always focus on recapturing size in any of the 3/4 F2's with a B allele showing. Then you can pick up the BB as 1/4 in a subsequent generation of maybe half dozen plants.

To get the size back, I would aim for 20 plants if you can do it. It is not easy and the ratio of 1 in 10 which Frogsleap found, may still not be quite full size of the largest parent. Chris can probably work out the ratio exactly, I'm just estimating. You would need more than ten to get one which also has a Beta allele. (I think the math is something like: 1/10 X 3/4 = 3/40 so roughly one in 14 plants might be large and Beta-allele, that is before probability calcs)

You could instead just aim to recover a Beta/- with the multi-locule trait fas, using perhaps 1/2 dozen plants, with the plan to take the largest multilocule fruit B/- or B/B and backcross it to CG or side cross to another larger fruit parent when you have selected a B/B full Beta.
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