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Genetic Recombination and Spatial Chromosome Relations in Maize Ming-Hung Yu Iowa State University

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Genetic Recombination and Spatial Chromosome Relations in Maize Ming-Hung Yu Iowa State University Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1972 Genetic recombination and spatial chromosome relations in maize Ming-Hung Yu Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Agricultural Science Commons, Agriculture Commons, and the Agronomy and Crop Sciences Commons Recommended Citation Yu, Ming-Hung, "Genetic recombination and spatial chromosome relations in maize " (1972). Retrospective Theses and Dissertations. 5879. https://lib.dr.iastate.edu/rtd/5879 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This dissertation was produced from a microfilm copy of the original document. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the original submitted. The following explanation of techniques is provided to help you understand markings or patterns which may appear on this reproduction. 1. The sign or "target" for pages apparently lacking from the document photographed is "Missing Page(s)". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting thru an image and duplicating adjacent pages to insure you complete continuity. 2. When an image on the film is obliterated with a large round black mark, it is an indication that the photographer suspected that the copy may have moved during exposure and thus cause a blurred image. You will find a good image of the page in the adjacent frame. 3. When a map, drawing or chart, etc., was part of the material being photographed the photographer followed a definite method in "sectioning" the material. It is customary to begin photoing at the upper left hand corner of a large sheet and to continue photoing from left to right in equal sections with a small overlap. If necessary, sectioning is continued again — beginning below the first row and continuing on until complete. 4. The majority of users indicate that the textual content is of greatest value, however, a somewhat higher quality reproduction could be made from "photographs" if essential to the understanding of the dissertation. Silver prints of "photographs" may be ordered at additional charge by writing the Order Department, giving the catalog number, title, author and specific pages you wish reproduced. University Microfilms 300 North Zeeb Road Ann Arbor, Michigan 48106 A Xerox Education Company 72-26,956 YU, Ming-Hung, 1936- GENETIC RECOMBINATION AND SPATIAL CHROMOSOME RELATIONS IN MAIZE. Iowa State University, Ph.D., 1972 Agronomy- University Microfilms. A XEROX Company, Ann Arbor, Michigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED. Genetic recombination and spatial chromosome relations in maize by Ming-Hung Yu A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Subject: Agronomy (Plant Breeding: Cytogenetics) Approved; Signature was redacted for privacy. In Charge of Major Work Signature was redacted for privacy. F/^ the Major Department Signature was redacted for privacy. For the Graduate College Iowa State University Ames, Iowa 1972 PLEASE NOTE: Some pages may have indistinct print. Filmed as received. University Microfilms, A Xerox Education Company il TABLE OP CONTENTS Page INTRODUCTION 1 LITERATURE REVIEW 4 Diversity in Exchange Potential Within a Genome 4 Genes on chromosome 4 Crossing over and the centromere effect 6 Compensating exchange with a genome 9 Other factors affecting crossing over 15 The Phenomenon of Intragenic Recombination 1? Genetic fine structure in microorganisms 17 Gene conversion - nonreciprocal recombination 19 Recombination and polarity 23 Association of conversion and crossing over 2.5 Intragenic Recombination at the wx Locus 26 Methods of investigation 26 Factors affecting intragenic recombination 28 Chemistry of the Waxy Phenotype 29 The components of maize starch 29 Starch synthesizing enzymes 31 The reaction of starch with iodine 3^ MATERIALS, METHODS AND SYMBOLS 36 Gene Symbol and Definition of Terms 36 Source of Materials 37 Development of the Waxy-Translocation Combinations 41 Step 1 41 Step 2 41 Step 3 42 Step 4 42 Step 5 45 The Location of the wx Locus and the Length of the Rearranged Chromosome 46 Ill Page Pollen Collection and the Recombination Assay 48 RESULTS 50 Comparison of the Vfe Frequencies between Inbred and Outcross Sources of Parental Homoalleles on Standard Chromosome s 51 Comparison of the Wx Frequencies between Homo- allelic and Heteroallelic Combinations on Standard Chromosomes 5^ Comparison of the wx Recombination Values of All Interchanges with the Controls: Heteroallelic Homotranslocation vs. Heteroallelic Standard Chromosomes 59 Comparison of the Recombination Frequencies of the Same Heteroallelic Combination among Different Interchange Chromosomes 60 Variation in Percentage Change of the ^ Frequency from Control among Different Heteroallelic Com­ binations with the Same Translocation 67 Comparing the Wx Frequencies among the Homoallelic Combinations on Standard and Homotranslocation Chromosomes 69 Effect of Environment; The Effect of Different Years on the ^ Reversion Frequencies among Various Allelic Combinations 73 DISCUSSION 81 Development of Waxy-Translocation Lines 81 Analysis of the wx Intragenic Recombination 84 Characteristics of the wx Alleles 86 The Position of the wx Locus and the wx Intragenic Recombination 87 The wx Intragenic Recombination Study and Its Possible Extension 89 Iv Page SUMMARY AND CONCLUSIONS 91 BIBLIOGRAPHY 9^ ACKNOWLEDGMENTS 105 1 INTRODUCTION The tendency of parental combinations to remain together Is termed linkage; genes show linkage because they are on the same chromosome. When new combinations of linked genes occur they are referred to as recombination events. Genetic loci are arranged in a linear order, and recombination can occur within a gene as well as between genes on the same chromosome. Within a genome there is a wide diversity in recombina­ tion among chromosomes. Crossover frequency per unit of physical distance varies throughout the chromosome, because the centromere exerts a marked influence on the rate of cross­ ing over in its neighborhood. In order to investigate varia­ tion in recombination throughout the maize genome a standard marker, waxy locus, in maize has been relocated to various positions in this study. The gene, the unit of function, can be subdivided into many linearly arranged structural elements. This has been demonstrated for numerous loci among microorganisms. With most higher organisms, however, it is difficult to determine whether the functional unit is subdivisible by recombination. The difficulty is at least partly due to the technique of handling, collecting and screening sufficiently large number of progeny to detect rare recombination events. In maize, a higher plant, intraoistron mapping has been demonstrated by Nelson (1959» 1962) with a sensitivity 2 approaching that available in microorganisms. This is based on the differential staining reaction of starch in pollen of different genotypes. It is possible to use the pollen grains as the unit of observation in genetical investigations on the waxy locus, because the starch composition of a haplold pollen grain is determined by its own genotype (Demerec, 192^; Brink and MacGllllvray, 1924). Pollen grains with waxy (wx) alleles stain reddish brown in iodine-potassium iodide solution; whereas non-waxy (Wx) pollen stains dark blue. Therefore, In wx plants genetic recombination at this locus can be demon­ strated by the appearance of dark blue staining pollen (Wx). This technique has a distinct advantage in genetic investiga­ tion with maize in that large populations of hundreds of thousands of genotypes (pollen grains) can be obtained and scored relatively easily. Intragenic recombination can be determined from the possible single crosses (P^) among a given number of different wx alleles. If the frequency of Wx pollen grains from the plant is significantly higher than the mean of the Wx frequen­ cies in the parental stocks, it is indicative of genetic recombination between two mutant sites of the wx locus. This frequency also reflects the distance between different mutant sites. Nelson (I968) has studied an extensive series of crosses from the Independently originating wx mutants on the standard chromosome 9* It has been known that recombination frequency between 3 two genes Is determined by the position of the genes In rela­ tion to the centromere and not the specific nature of the section of chromosome Itself (Beadle, 1932» Graubard, 1932). The frequency of crossing over Increases as one approaches the middle of the chromosome arm, and Is greatest In the distal half of the chromosome. However, the effect on recombination frequency In changing the position of the wx locus from the centromere In a maize genome has never been determined. This study Is concerned with whether Intragenic recombina­ tion at a given locus Is affected by changes In position of this locus In the genome. What effects will
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