5. Crosses between interchanges involving the same two chromosomes.

T2-4a × 2-4c = semisterile F1
T2-4a × 2-4b = "
T2-4b × 2-4c = "
T2-6c × 2-6d = 20% sterility on ears, pollen also low
T2-9a × 2-9b = semisterile
T5-7a × 5-7c = 29% sterility on ears (pollen also low)

The low sterility was thought to be the result of survival of a certain class of spores which ordinarily aborts. In crosses involving two interchanges in which the two breaks are close together and in the same relative position with respect to the spindle fiber (the same interchange having its break in each chromosome closer to the spindle fiber than does the other one) certain spore classes should be deficient for only one short region. According to the cytological date available, in T2-6c the breaks are in the long arms at .3 and .25 respectively from the S.F. in chromosomes 2 and 6; while in 2-6d they are also in the long arms but at .4 and .4. Deficiency tests for genetic loci in the two F1 hybrids showing low sterility were all negative:

for T2-6c × 2-6d: ms, si, pb were tested for chromosome 6
lg gl v4, ba2, ts were tested for chromosome 2.
T5-7a × 5-7c: bv gl6 for chromosome 5
sl, bd, gl, ra ij for chromosome 7

It seems probable that none of the genes tested is in the region suspected of being deficient.

C. R. Burnham