Cytogenetic studies of tetraploid hybrids of Euchlaena perennis and Zea mays
Shaver, D.L.
Dissertation Abstracts 21: 1033-1034
1960
ISSN/ISBN: 0099-3123 Accession: 014003352
Segregation of 11 markers was significantly altered in hybrids between Ax maize and Ax E. perennis, in comparison with the maize controls. Coefficients of preferential segregation ranged from 0.399 to 0.869. Genetic ratios from the Ax hybrids indicated a degree of chromosome homology intermediate to that found by geneti-cal analysis for species belonging to five other genera (unspecified). The comparison suggested that the relationship between Zea and Euchlaena is congeneric. Linkage, as measured by the coefficient of 4x linkage, was stronger in the hybrids than in the maize controls for four of the six regions analysed. This result was consistent with cytological observations indicative of a reduction in chiasma frequency in the hybrids. In segment wx-C, crossing over was higher in frequency than in maize, in spite of the fact that no crossing over occurred in the overlapping wx-sh1 and wx-yg2 regions. Inheritance of C thus appears to be irregular in the hybrids. The apparent increase in crossing-over frequency in region Y-Pl in the hybrids may be due to the fact that the frequency of chromosome-6 quadrivalents involving partner exchanges is twice the average frequency for the other nine chromosomes. The clone of E. perennis used as parent was heterozygous for sh1 and is probably triplex. The range in 2n number in the progeny of a randomly intercrossing population of 92 Ax maize plants was similar to that in the progeny of 40-chromo-some individuals. The distribution of numbers within the range of 36 to 43 was, however, significantly skewed towards hypoploidy. Chromosome numbers in the hybrids varied from 29 to 44, this range being significantly greater than in either of the maize populations. E. perennis had a quadrivalent frequency of 0.499, as against 0.871 in 4x maize. Quadrivalents were restricted to two types in E. perennis, whereas ten types were recognized in Ax maize. "These observations are compatible with a reduction of chiasma frequency to one or less per single chromosome arm in E. perennis. The minimal chiasma number, as estimated from quadrivalent configurations, is 3.879 in E. perennis, as compared to 4.202 for Zea, and 4.045 in the hybrid." Correlated cytological and genetical data from chromosome 6 indicated that its bivalents were in most, and probably all, cases homosynaptic, since random disjunction for chromosome-6 quadrivalents satisfactorily accounted for the observed frequency of recessive gamma gametes.