E. W. Lindstrom

Genetics of polyploidy

ConclusionIn general, then, genetic evidence from polyploids harmonizes surprisingly well with concepts based on the modern gene-chromosome law of heredity. This is true for both the individual hereditary characters and the organism as a whole. With the former, it is evident that character inheritance follows the particular gene distribution even when the cytological mechanism is disturbed by the addition of chromosomes.The organism as a whole is also influenced by polyploidy but the relations of the parts are, nevertheless, maintained. The addition of one chromosome in a trisomic, for example, alters many individual characters and upsets the favorable balance of plus and minus factors established in the diploid by long continued selection. Nevertheless, the plant continues to function as a whole. This can mean only that there is a high degree of elasticity in an organism, affording a margin of safety for variable conditions. This may well explain the success of the mutation theory of evolution in giving new mutations time to become established and to become fitted into the germinal complex in which they arose. True polyploidy affords, in addition, extra gene loci as sources for new mutations. Such extra loci, as they mutate, must preserve a correlated function with their original sister loci and the polyploid condition would seem to afford time and protection for this process.

Linkage of Qualitative and Quantitative Genes in Maize

SEVEN years ago I commenced a series of investigations to test for the presence of genes for quantitative characters in the known linkage groups of two species, one a cross-fertilized type, Zea wtays, and the other a naturally self-fertilized species, Lycopersicumn esculenturin. In the latter I have already reported (1924, 1926 and 1928) that genes controlling fruit size of the tomato show genetic linkage with qualitative genes on the first three chromosomes of that species. In maize, a great mass of data bearing on a similar situation has been collected. Since this will necessitate publication in several long reports, it seems well to present a brief summary of the results, giving a general picture of the relations discovered. Number of rows on the maize ear was chosen as a typical quantitative character (East, 1910; and Emerson and East, 1913). A suspicion that some genetic correlation might exist between row number and cob color, for example, was aroused by the fact that all known eightrowed varieties of maize have the white-cob, none are red-cobbed. Accordingly cob color and other qualitative characters, such as aleurone and endosperm color as well as endosperm texture, were brought into the problem. Commercial varieties of maize inbred for only one generation served as foundation stock for the crosses. To have inbred them more would undoubtedly have introduced another variable, namely, that the inbred line chosen might not have represented the main varietal characteristics. It would, however, have given a sharper definition to the resulting data. The following varieties were used:

Genetical research with maize

INTRODUCTION. DESCRIPTION AND INHERITANCE OF GENETIC CHARACTERS. EAR CHARACTERS. ENDOSPERM CHARACTERS. PLANT CHARACTERS. CHLOROPHYLL CHARACTERS. ANTHOCYANIC OR .PLANT COLOR CHARACTERS. VARIEGATION AND MUTATION, LINKAGE GROUPS OF MAIZE. RELATIVE FREQUENCY OF CROSSING OVER IN MICROSPOROGENESIS AND IN MEGASPOROGENESIS. EFFECTS OF INBREEDING IN MAIZE. ALPHABETICAL LIST OF GENETIC FACTORS IN MAIZE. BIBLIOGRAPHY.