Chromosome Segregation in Maize Translocations in Relation to Crossing Over in Interstitial Segments

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Abstract
In maize translocation heterozygotes which form rings and have short interstitial segments (low crossover frequency), alternate segregation occurs in about 50% of the meiocytes. In them, both types of adjacent segregations occur, not always with equal frequency but the total is roughly 50%. In those with interstitial segments long enough to permit a high crossover frequency there is little or no adjacent 2 segregation. The segregation in rings differs greatly from that in chains. In chains, there is little or no adjacent 2 segregation whether the interstitial segment is long or short (in terms of crossing-over). There is, therefore, no evidence of any directed segregation in the maize translocations studied, even with greatly break positions. This, together with Catcheside''s observations that segregation is directed even in unequal translocations produced by X-raying an Oenothera race with 7 pairs, suggests that directed segregation may be genetically controlled. Even in a species homozygous for such a genotype, translocations with long interstitial segments should have considerable sterility as a result of crossing-over in those seg- ments, reaching 50% as a possible maximum. According to the literature, the translocations that have survived in Oenothera are those with short interstitial segments. These, therefore, would have low sterility from that source. A search for genes in maize affecting segregation is being made by crossing stocks of widely different origin with translocations having short interstitial segments.
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