It's 2023

 I did not blog much in late 2021.  In 2022, I did not grow tomatoes at all, for the first time in many years.

As 2023 starts, I discovered some unfortunate news about my 55a7 x pBTD cross that I began a few years ago.  My goal here was to combine purple skin and green stripe.  In 2021, I collected seeds from F2 fruit, thinking that 1/16 would be atv/atv ; gs/gs , but at least some of the atv/atv that were not green stripe might also be gs/+ and thus worth breeding out to F3 in order to homozygose gs.   

Well.  This is a fine plan under the assumption that atv and gs are completely unlinked.  What are the odds?  Turns out they are tightly linked on chromosome 7.    I got the genome locations based on close markers from separate publications.   

Green stripe:   SNP marker SL2.50ch07_63842838

(Liu et al. New Phytologist, 2020.  GREEN STRIPE, encoding methylated TOMATO AGAMOUS-LIKE 1, regulates chloroplast development and Chl synthesis in fruit)

atv:  within SL2.50ch07: 60999091–61004074

Cao et al/. J Exp Botany 2017 -  A putative R3 MYB repressor is the candidate gene underlying atroviolacium, a locus for anthocyanin pigmentation in tomato fruit)

These are about 2.8 Mb apart, which I estimate to be about 4 cM based on the Tanksley map from 1992 (Genetics).

So - this means that the F1 was atv-+ / +-gs for chromosome 7.

For an F2 to be atv-gs / atv-gs , it would have to inherit two crossover chromosomes from the F1.  Odds of each are about 2%.  Odds of inheriting both are 1/2500.

What's also bad is that although I saved some F2 atv/atv seeds, these are about 98% likely to be homozygous wild type for gs - so they are not worth breeding out to get gs phenotype.

I suppose I could plant some F3 from the largest F2 purple fruit, just to see if I can a big size purple - gf line that is bigger than my old 46A2 line.  Try #18 maybe.