3. Chromosome segments from Florida teosinte. The segments of chromatin or blocks of genes which distinguish Florida teosinte and maize have been transferred by repeated backcrossing to a uniform inbred strain of maize. Two of these have now been crossed with the nine-gene multiple tester stock previously mentioned and backcrossed to the multiple recessive. Here we are studying only the dominant effects of the chromatin segments from teosinte.

One of these segments proved to be linked with A on the third chromosome the other with Su on the fourth. In both cases the segments are somewhere near the center of the chromosome, the segment on the fourth includes the Su locus, the segment on the third shows approximately 25% crossing over with A, which is known to be near the end of the chromosome. Both segments have the same kinds of effects. Both reduce the number of rows of grain, the size of the seed and affect the development of the pistillate glume structure.

The segment on the third chromosome is usually inherited intact but that on the fourth is frequently broken as a result of crossing over. Parts of the segment have the same general effects as the entire segment, but in a smaller degree.

It is quite possible that the problem of inheritance of row number in maize is complicated by small segments of this kind originally derived from Tripsacum through admixture with teosinte. The crosses of Nobogame and Durango teosinte previously mentioned showed that genes involved in the difference between the two-ranked and the many-ranked condition occur on at least seven of the nine chromosomes tested. These are probably the same kind of genes which account for differences in number of rows of grain in some varieties of maize.

Summary of Linkages in Teosinte Crosses

+     = Linkage

I     = Indication of Linkage

-     = Independent Inheritance

*     = Deviation in Direction of Repulsion

P. C. Mangelsdorf