Analysis of Variance and Covariance of Chromosomal Association and Behavior During Meiosis in Clones of Dactylis glomerata

Abstract

1. Data on chromosomal association and behavior during meiosis were collected from three replications of each of six clones of Dactylis glomerata L. for two years, 1940 and 1941, and of three additional clones for one year, 1941. Statistically significant differences among clones were found for number of half-chiasmata per chromosome, average number of quadrivalents per sporocyte, frequency of unpaired chromosomes at metaphase I, frequency of lagging and dividing univalents at anaphase I, and frequency of micronuclei in the quartets. All characters were recorded in both years except chiasma frequency, which was recorded only in 1941. For all the characters recorded in both years the interaction of clones x years was significant, while the difference between years was significant only for frequency of univalents at metaphase I and for frequency of micronuclei in the quartets. 2. From analyses of covariance, correlation coefficients were calculated for the various characters. The correlation coefficients (r) of quadrivalent frequency with frequency of metaphase I univalents and with frequency of anaphase I laggards were not significant, while r of chiasma frequency with metaphase I univalents was negative and significant. Significant positive values of r were obtained between chiasma frequency and quadrivalent frequency, metaphase I univalents and anaphase I laggards, metaphase I univalents and micronuclei in the quartets, and anaphase I laggards and micronuclei in the quartets. 3. By means of analyses of covariance, it was found in all but one case that there were significant differences among plants in the dependent variable which could not be ascribed to its regression on the independent variable. In the exceptional case all significant differences among plants in occurrence of laggards at anaphase I could be accounted for by variations in frequency of metaphase I univalents. 4. It is suggested that in D. glomerata unequal distribution of chromosomes from quadrivalents is of minor importance in conditioning other meiotic irregularities. On the other hand, the presence of unpaired chromosomes at metaphase I which lag and divide longitudinally at anaphase I, tending to be left in the cytoplasm at telophase I or telophase II, appears to play a major role in that regard. Three of the nine clones had low frequencies of metaphase I univalents and consequently few laggards at anaphase I and few micronuclei in the quartets. 5. Significant differences among clones suggest the possibility of selecting lines of D. glomerata which would be more regular in meiosis and possibly more fertile. The relationships found among the various characters of meiosis serve as a guide for selection.