32. The cytological identification of the chromosomes associated with the
‘R-golden’ and ‘ B-liguleless’ linkage groups in Zea mays. Barbara MeClin-
tock and Henry E. Hill, Cornell! University.

The smallest chromosomes of the normal set (Science, vol. 69, p. 629, 1929)
carries the gene of the r-g linkage group. 2n +1 plants triplex for this chromo-
some give trisomic ratios for the factor pair B-r when selfed, sib-crossed, and
back-crossed. These plants showed disomic ratios for C-wz, su, b, y, gl-vs, pr,
and @. Plants triplex for the r-g chromosome differ only slightly in appearance
from the normal diploids. In 2n +1 plants the extra chromosome is transmitted
through one-third of the eggs. Only a small percentage of n +1 pollen grains
function in competition with a grains (rr? X EEr gd gave 941 colored to 486
colorless kernels, 2: 1 expected; rr9 x Rrr gf gave 1392 colored to 2685 colorless
kernels, 1:2 expected). The fourth largest chromosome carries the genes of
the b-lg linkage group. 2n-+ 1 plants triplex for this chromosome give trisomic
ratios for %, b, and ig. These 2n +1 individuals show a markedly decreased
vigor. The extra chromosome is carried through one-fourth of the eggs, but is
seldom transmitted through the pollen (lglg 2 X Lolglg $ gave 344 Lg: 163 Ig,
2:1 expected; igig 2 X Lglgig g gave 276 Lg: 542 lg, 1:2 expected). The
genetic investigations have been undertaken With the cooperation of Marcus M.
Rhoades and George W. Beadle.