VIABILITY ESTIMATES FOR SIXTY TOMATO MUTANTS

Abstract

Monogenic segregation data for 60 mutants show that for 42 of them the observed number was less than the expected and 25 of these 42 were significantly less. In many cases the discrepancy was too small to de detected in populations; of less than 500 plants. In no case was the mutant more viable than the wild type allele unless one accepts data for mutants H and o which appear to be cases of misclassification. The cause of the inviability was obvious in many cases where the mutant was slow growing (I, dil, tf), or poor germinating (ro, au, dpy), but in many cases the mutant wais as vigorous as the wild type. There were two types of change in viability, in the first case newly arisen mutants became more viable as the result of selection on different genetic backgrounds, in the second case there was a sudden change in viability because the mutant became associated in coupling phase with a lethal gene. The segregation ratios of genes at the proximal end of chromosome 2 are affected by the gametic eliminator (gt) whereas segregations in the central region, in the vicinity of aw, are affected by a chromosomal rearrangement. Genes at the distal end of chromosome 2 may have distorted ratios because of a lethal near the bip locus. The importance of uniform background and planned experiments is pointed out.