Theoretical consideration of the origin of gene-for-gene relationships led to the conclusion that such relationships, postulated by Flor for the Linum:Melampsora system, should occur as a general rule in host:parasite systems. An ideal gene-for-gene system, with five related host and parasite loci, was designed to illustrate the properties inherent in gene-for-gene systems, and to illustrate a new method of analyzing for these properties. Analyses of published data of the Solanum:Phytopthora and Linum:Melampsora systems proved that gene-for-gene relationships are in fact operative in these systems and that Flor's hypothesis—that for each specific locus in the host determining resistance and susceptibility there is a specific and related locus in the parasite which determines virulence and avirulence—is correct. Analysis of Flor's data showed, however, that most of his "single-gene" differential varieties actually possess two or more genes for resistance, and that resistance genes in these varieties need not fall into allelic or closely linked groups.

Bivalents, univalents, end-to-end and side-by-side associations, also chromosome distributions to the poles were associatively recorded for each of approximately 2000 meta-anaphase cells of a haploid Triticum aestivum L. It was demonstrated that the distribution of the univalents to the polar groups was not random. An inverse relationship between side-by-side association and bivalent frequencies was also demonstrated, and this formed the first in a series of analytical steps which led to a description of chromosome movement in the haploid. The validity of certain assumptions concerning chromosome behavior was tested using the χ2 method; for others, confirmatory observations were made in monosomic cells.

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Meiotic chromosome behavior was described for a group of monosomic plants, including representatives of the F1 and the first to seventh backcross generations. All plants were partially asynaptic. Rings-of-four were commonly seen in F1. and early backcross generations. Irregularities occurring among the progenies of monosomics were also described. These included monosomic plants which, through a process termed univalent-shift, were deficient for chromosomes other than those deficient in their respective monosomic parents. It was concluded that the irregular karyotypes occur as a consequence of partial asynapsis in the parent monosomics.