Location of the recessive gene ym (yellow margin) on chromosome 12 of diploid Solatium tuberosum by means of trisomic analysis.

Ten out of twelve primary trisomics of dip-loid S. tuberosum were crossed as females with a recessive mutant for yellow margin (ym ym) obtained from S. phureja. All primary trisomics used proved to be homozygous dominant. Trisomic plants from all ten F1's were backcrossed with the mutant and trisomics from eight F1's were crossed also with a disomic heterozygous f1 plant from triple 10 X mutant.In both BC1 and half sib progeny of each trisomic type the mutant plants were easily identified because of their typical small roundish leaflets with yellow or reddish margins. The observed segregation ratios for normal to mutant were tested against the expected non-critical ratios and against various expected critical ratios.From the results of these tests it is concluded that the gene ym is located on chromosome 12 of the potato. A hypothesis of linkage between ym and a gene l x for lethality is put forward. It is concluded that l x is not identical with a previously detected recessive gene l 2 which is responsible for yellow cotyledons and lethality.