Chromosome 7.

Certain stocks of the late Professor A. C. Fraser, and several of the co-op stocks as well, contain a factor for defective seeds. This recessive factor reduces seed size to 1/16 - 1/4 that of normal and is somewhat variable in expression. Defective seeds entirely fail to germinate in weak lines but may produce 1/4 - 1/8 sized plants in vigorous stocks. As a new defective seed mutant, this one would hardly command any attention. However, this semi-lethal was isolated by selfing cultures containing the genes in v5 ra gl and these same cultures had previously shown unequal parental and crossover classes in 3 point tests. One may presume that this semi-lethal is linked rather closely with those markers and is the cause of these aberrant ratios. It is unlikely that this recessive by itself can account for the marked differences obtained in linkage results in different lines, unless it has an effect on crossing over when present in the heterozygous condition. This has not been studied. One might easily ascribe ears segregating for this gene to the effects of poor pollination, but ears segregating approximately 3:1 have been recovered from normal seeds taken from a segregating ear.

M. J. Murray