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Cuphea is an herbaceous genus having species whose seed storage lipids are predominantly medium-chain triglycerides (MCTs). Cuphea lanceolate Ait, and Cuphea viscosissima Jacq. are central to the breeding of Cuphea as a new commercial source of MCTs. The objectives of this thesis were to develop a reliable method to extract DNA from Cuphea, to construct a molecular-marker linkage map of C. lanceolate, and to evaluate quantitative-trait loci (QTL) affecting seed capric acid content, seed oil content, and embryo development in C. lanceolate. We used allozyme and restriction-fragment- length-polymorphism (RFLP) markers to study Cuphea because molecular markers are the best method available to investigate the Mendelian genetics underlying quantitative traits, and are useful in breeding. Adequate yield of clean DNA is essential for RFLP mapping. We tried numerous DNA extraction methods that failed to remove contaminants that interfere with restriction digests of Cuphea DNA. The method described here was developed to remove those contaminants and maintain relatively high DNA yields. In this method, the critical step in purification consists of washing the DNA with phenol while it is complexed with CTAB and dissolved in 1 M NaCl. An RFLP and allozyme linkage map of C. lanceolate was constructed having 37 markers in six linkage groups with a total distance of 288 cM. Levels of polymorphism were estimated for three lines of C. lanceolate and one line of C. viscosissima using 84 random genomic clones and two restriction enzymes, EcoRI and HindIII. Twenty-nine percent of the probes detected RFLPs between C. lanceolate lines, whereas 63% of the probes detected RFLPs between C. lanceolate and C. viscosissima lines. Thirty RFLP and four allozyme markers were used to locate on the C. lanceolata linkage map QTL affecting seed capric acid content, seed oil content, and embryo development. Three unlinked QTL explained 19.4% of the phenotypic variation in capric acid content in F₂ seed. Seed oil content and seed weight were measured on seed from field-grown F₂ plants. Seed weight was indicative of embryo size (development). Four unlinked QTL explained 33.9% of the phenotypic variation in embryo size. One of these QTL, which explained 20.3% of the variation, may have been a chromosomal deletion detected by a marker having a null allele. Three QTL pleiotropically affected seed oil by affecting embryo size. The one QTL that only affected seed oil accounted for 2.8% of the phenotypic variation. / Graduation date: 1991

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.