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Genetic characterization and mapping of the Semigamy mutant of cotton (Gossypium barbadense L.)
Abstract
The time and mode of gene expression of the Semigamy mutant was examined by developing a genetical-statistical analysis based on a novel application of joint-scaling tests. A 3x3 factorial mating of genetically-marked parents was used to produce 9 populations, each of which was subsequently evaluated for haploid /chimera frequencies. These data were analyzed by use of joint-scaling tests based on genetic models that distinguished among various types of parental sporophytic, gametophytic, and zygotic genetic source effects. Chi-square tetests indicated that the Semigamy gene was expressed at the Semigamy gene was qualitatively inherited. The regression and associated t-sts of the genetic effects models demonstrated their validity, and that the sporophytic level as an incompletely dominant allele, and that maternal genotypic influence was strong, whereas paternal genotypic influence was moderate. A modified method of deficiency mapping was used to associate the Semigamy locus with a chromosome and/or chromosome segment. Semigamous hypoaneuploid F, stocks were derived by crossing semigamous line 57-4 (SeSe) with nonsemigamous (sese or se-) monosomic, monotelodisomic, and duplication-deficient types as female, that provided coverage for 38/52 chromosome arms. The F, semigamous aneuploids were testcrossed to nonsemigamous'S6' Pima females to produce 5 or more BC,FL plants per F, aneuploid. BCIF,'s were individually tested to determine haploid/chimera frequencies by evaluating 300+ Si progenies for each. Only the BC,FL families from F, plants deficient for chromosome 4 or the short arm of chromosome 4 were uniformly semigamous, which indicated that these F, plants were hemizygous (Se-), and that the Semigamy locus mapped to the short arm of chromosome 4. To more efficiently recover Semigamy induced haploid progenies, a statistical selection technique, based on seed weight, was devised. Seeds from 4 populations, 2 homozygous semigamous lines and the reciprocal crosses between them, were weighed and divided into discrete weight classes. Both raw and transformed seed weights were analyzed, and plotted against the numbers in each weight class per population and against haploid and chimera frequencies. The results indicated that a truncated selection regime based on -2.0 standard deviations from the mean seed weight would increase the 1 to 5% average haploid recovery rates to 37 to 1 00%. The weight distributions of chimeras was much more normal, and selection by weight would not be effective.
Description
Vita.Collections
Citation
Gwyn, Joseph Jefferson (1995). Genetic characterization and mapping of the Semigamy mutant of cotton (Gossypium barbadense L.). Texas A&M University. Texas A&M University. Libraries. Available electronically from https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1574763.
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