In order to trace the inheritance of chromosome knobs and how their expression may or may not change through successive generations, the race Chapalote with internal knobs was crossed with Zea diploperennis with terminal knobs. Cytological material from specific parent plants and their F1 progeny was studied for precise comparison of chromosomes.
Theoretically, if the two parental strains were homozygous for knobs, the number found in the F1 generation should equal half the sum of the total number of knobs in both parents. However, if the knobs are heterozygous in the parents, there will be segregation and variation in the knob number of the F1 plants. Pure inbred lines were not used and the material is heterozygous.
Table 1 shows the number of knobs observed and counted in examinations of cells from specific plants of Z. diploperennis, Chapalote, the F1 progeny, and the expected range in knob number for heterozygous F1's. Analysis of the data reveals two points. First, there is a higher number in the range of internal knobs than the expected maximum number contributed by both parents. Secondly, there is a lower range in the number of terminal knobs in the F1 hybrids than would be the expected minimum. This suggests that terminal knobs of diploperennis may shift to internal positions when hybridized with maize.
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