crosses of the F; hybrid to the WMT maize stock pro- 
duced triploid plants having 20 maize and usually 18 
Tripsacum chromosomes. The second backcross to W MT 
yielded a population of 92 plants segregating for varying 
numbers of extra T'ripsacum chromosomes, ranging from 
one to thirteen, of which seven were marked by dominant 
genes. 
Our genetic analysis (Galinat, Mangelsdorf and Chag- 
anti, 19638) of the transmission frequencies of the seven 
dominantly marked Tripsacum chromosomes indicated 
a negative answer to the second question: 7.e., does 
Tripsacum carry the dominant alleles in duplicate? The 
frequencies of these dominants were similar, averaging 
32.2 per cent with the exception of J; which was present 
in almost twice this frequency (Table IV). We now know 
that at least part of the high frequency of Ji was the re- 
sult of a poor expression of 7; which is characteristic of 
this gene. The progeny of another generation of back- 
crossing to WMT of one plant classified as Ji proved to 
be all.j1, while another similar backcross progeny proved 
to be all green, perhaps because of the presence of one 
of the R# alleles which is known to be associated with a 
factor inhibiting the expression of 7; (Emerson, Beadle 
and Fraser, 1935). 
The average transmission frequency of 32.2 per cent 
for each dominantly marked chromosome (except J1) was 
interpreted as a deviation from the expected 50 per cent 
on random segregation of a single chromosome. This was 
Tasir IV. Genetic data for transmission rate to 92 WMT maize plants 
of seven dominantly marked 7’. dactyloides chromosomes derived from 
a maize-Tripsacum BC, hybrid. 
Maize Chromosome 
] ? 3 4 t 8 9 
Dominant from Tripsacum Bm, Lg, <A, Su, Gl, J, Wx 
Frequency of Dominants, % 34.5 23.9 31.6 28.2 38.0 60.5 37.0 
[ 8303 ] 
