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A Genetic Evaluation of Methods of Utilizing Heterozygosis and Dominance in Autotetraploids 1
Author(s) -
Dudley John W.
Publication year - 1964
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1964.0011183x000400040024x
Subject(s) - geneticist , dominance (genetics) , library science , biology , citation , genealogy , computer science , history , genetics , gene
To simplify analysis of the problem the following assumptions were made: a) alpha (coefficient .of double reduction) ~ 0; b) alleles per locus; c) inbreeding occurs without selection; d) 100% crossing when matings are made. The further assumption was made that the information of value concerning crossed populations is either the percent of individuals heterozygous (overdominance hypothesis) or the percent of individuals containing at least one dominant allele in the genotype (dominance hypothesis). Under these assumptions there are 5 possible genotypes at a given locus, designated A~, A~, A?, A~, and A°, where the superscripts denote the number of A alleles in the genotype. Among 5 genotypes there are 15 possible single-cross mating types. Thus the single-cross mating type A* X A~, coded as 43, represents a cross between quadruplex and triplex individuals or random selfed lines from them. Crosses between two such single-crosses (e.g., 44 X 43) are referred to as double ,crosses. To determine the percent heterozygosity or percent dominance in a given crossed population under different conditions, the generation matrix results of Demarly* were used to obtain the genotypic distribution in a given selfed generation for a particular mating-type. From the genotypic distribution of the selfed lines, the gametic output of each line was calculated. By multiplication of the gametic distributions of the parents involved, the genotypic distribution of the crossed progeny was determined. From this genotypic distribution, the percent heterozygous and percent dominant individuals were determined. For example, consider the mating-type A~ X A~ in the S~ generation (Symbols So, &, S~, S~ refer to non-inbred, Erst selfed, third selfed, and homozygous generations respectively). The genotypic distribution will be 1⁄4A~ + 1/2A~ + 1/~A~ from the A~ parent and all A~ from the A~ parent. The corresponding gametic distributions will be 13/24 AA + 10/24 Aa -}1/24 aa from A~ and all AA from A~. Multiplying these gametic distributions results in 13/24 A4 -~5/12 A~ q1/24 A~ in the F~ or, as shown in Tables 1 and 2, 45.8% heterozygous and 100% dominant genotypes. Gametic distributions from the single crosses thus obtained were used to compute genotypic distributions in double-cross progeny. In the section on 2: loci, the 2 loci were considered to be independent; hence, the percent A--B-individuals in a population was computed as the product of the proportion of A-individuals and B-individuals.