Abstracts of Papeks Presented at T H E 1939 Meetings of the Genetics Society of America

S OF PAPEKS PRESENTED AT T H E 1939 MEETINGS OF THE GENETICS SOCIETY OF AMERICA COLUMBUS, OHIO, DECEMBER 28-30, 1939 E. W. LINDSTROM, Secretary Department o j Genetics Iowa Stale College, Antes, Iowa ATWOOD, SANFORD S., U. S. Regional Pasture Research Laboratory, State College, Pa. : Cytogenetics of incompatibility in Trifolium repens.-Thirteen self-sterile F1 plants were crossed in all combinations and were backcrossed with their self-sterile parents. The F1 plants consisted of four intra-sterile, inter-fertile groups of five, four, three, and one plant, respectively, and all were reciprocally fertile with both parents. Using ten 5owers in each cross, compatible crosses averaged 44.9 seeds and incompatible 0.26. A second series of diallel crosses were made between 13F1 plants and their parents. One parent was self-sterile and the other highly “pseudo-self-fertile.” Both this latter parent and its progeny were practically self-sterile when individual 5owers were self-pollinated in either full flower or the bud, but they set selfed seed when the entire heads were rubbed to effect pollination. The factors conditioning this pseudo-self-fertility are independent of those causing cross-incompatibilities, since four intra-sterile, inter-fertile groups of four, four, three, and two plants, respectively were found in this second set of progeny. Compatible crosses averaged 41.9 seeds and incompatible 0.18. The results in both series of crosses are explained best by the diploid (16 bivalents found regularly) personate type of oppositional factors where the parents differ in both alleles. The 12 groups from the two series were compatible in all combinations, indicating a t least seven different allelomorphs in the four parents. Other evidence suggesting a large number of allelomorphs is that all matings (over 200) between unrelated plants were compatible. Few or no seeds were set in incompatible crosses because of poor pollen germination and pollen tube growth within a few hours after pollination. BANTA, S. M., Brown University, Providence, R. I.: Possible rdle of amixis in the evolution of organisms.-Experimental findings from parthenogenetic reproduction in Cladocera and other well authenticated facts suggest that amixis, particularly when alternating with amphimixis, may be a potent factor in evolution. In Daphnia, mutation in diploid parthenogenesis is moderately frequent-all of our recognized Cladocera mutations having arisen during parthenogenesis. Most of these mutations are recessives and their effects, almost exclusively physiological, are recognized only in the results of sexual reproduction-inbreeding within the clone involved. The relative frequency of occurrence of these mutations during parthenogenesis together with, in nature, the periodical occurrence of amphimixis suggests that in the amictic-amphimictic cycle abundant genic recombinations occur. GENETICS 25: 109 Jan. 1940