Chromosome polymorphism in Avena ventricosa

The same karyotype which was described previously in A. ventricosa plants from Oran, Algeria was found in plants from Cyprus and in most of the plants from the Apsheron Peninsula, U.S.S.R. This karyotype, which consists of subterminal chromosomes, was designated C _v ¹ . In the karyotype of about one-third of the Apsheron plants a single pair of submedian chromosomes replaced a pair of long subterminals. This karyotype was designated C _v ² . The chromosomes formed 7^II at meiosis in both C _v ¹ C _v ¹ and C _v ¹ C _v ² hybrids regardless of geographic origin. A heteromorphic bivalent was apparent in PMCs in the C _v ¹ C _v ² hybrids. A pericentric inversion was postulated as the origin of the submedian pair, the C _v ² C _v ² karyotype being the inversion homozygote. The absence of duplication-deficiency gametes was inferred from the good fertility of the heterozygote. Members of the heteromorphic pair were transmitted in equal proportion and the segregates C _v ¹ C _v ¹ , C _v ¹ C _v ² and C _v ² C _v ² were equally fertile; thus the inversion did not handicap reproduction. The small contemporary colonies of A. ventricosa, with peripheral locations and vast distances between them, because of the full homology and interfertility, are considered remnants of a formerly large central population.Contribution No 282 from the Research Station, Central Experimental Farm, Ottawa, Ontario.This paper is dedicated to the memory of Dr. Barna Györffy, whose untimely death on August 5, 1970 ended a distinguished career that was an example of integrity and scholarship to a troubled generation of Hungarian geneticists.     

Material recycling in a closed aquatic ecosystem. I. Nitrogen transformation cycle and preferential utilization of ammonium to nitrate by phytoplankton as an optimal control problem

A mathematical model of the nitrogen transformation cycle in an aquatic environment is studied. Using Pontryagin's maximum principle, a preferential utilization of ammonium to nitrate by phytoplankton is explained and verified by experimental data. A multiparameter bifurcation is given. The model was found to have four types of equilibrium sets. It is shown that a Hopf bifurcation may occur.