Restriction fragment length polymorphisms have become powerful tools for genetic investigations in plant species. They allow a much greater degree of genome saturation with neutral markers than has been possible with isozymes or morphological loci. A previous investigation employed isozymes as genetic markers to infer the location of genetic factors influencing the expression of quantitative traits in the maize population: (CO159×Tx303)F2. This investigation was conducted to examine the inferences that might be derived using a highly saturated map of RFLP markers and isozymes to detect quantitative trait loci (QTLs) in the same maize F2 population. Marker loci that were associated with QTL effects in this investigation generally corresponded well with previous information where such comparisons were possible. Additionally, a number of previously unmarked genomic regions were found to contain factors with large effects on some plant traits. Availability of numerous marker loci in some genomic regions allowed: more accurate localization of QTLs, resolution of linkage between QTLs affecting the same traits, and determination that some chromsome regions previously found to affect a number of traits are likely to be due to linkage of QTLs affecting different traits. Many of the factors that affected plant height quantitatively in this investigation were found to map to regions also including known sites of major genes influencing plant height. Although the data are not conclusive, they suggest that some of the identified QTLs may be allelic to known major genes affecting plant height.
Genetic linkage maps were constructed for both maize and tomato, utilizing restriction fragment length polymorphisms (RFLPs) as the source of genetic markers. In order to detect these RFLPs, unique DNA sequence clones were prepared from either maize or tomato tissue and hybridized to Southern blots containing restriction enzyme-digested genomic DNA from different homozygous lines. A subsequent comparison of the RFLP inheritance patterns in F2 populations from tomato and maize permitted arrangement of the loci detected by these clones into genetic linkage groups for both species.
When DNA molecules are injected into Xenopus oocyte nuclei, they can recombine with each other. With bacteriophage lambda DNAs, it was shown that this recombination is stimulated greatly by introduction of double-strand breaks into the substrates and is dependent on homologous overlaps in the recombination interval. With plasmid DNAs it was shown that little or no recombination occurs between circular molecules but both intra-and intermolecular events take place very efficiently with linear molecules. As with the lambda substrates, homology was required to support recombination; no simple joining of ends was observed. Blockage of DNA ends with nonhomologous sequences interfered with recombination, indicating that ends are used directly to initiate homologous interactions. These observations are combined to evaluate possible models of recombination in the oocytes. Because each oocyte is capable of recombining nanogram quantities of linear DNA, this system offers exceptional opportunities for detailed molecular analysis of the recombination process in a higher organism.
One hundred six commercial hybrids of current importance in U.S. maize, Zea mays L., production were profiled for 46 restriction fragment length polymorphism (RFLP) probes. Objectives were to (i) compare diversity among hybrids with that found among public lines; (ii) reveal associations among hybrids; (iii) measure the correlation between RFLP and pedigree distances; and (iv) determine the impact on diversity from the usage of similar genotypes. Of RFLP variants found among 150 public lines 82% were found among the hybrids. Only three variants found among the hybrids were not also found among public lines. The RFLPs, therefore, showed little evidence of exotic germplasm usage. Fifty‐three hybrids fell into 10 groups within which members shared 90% of their profiles; groupings based on higher levels of similarity were also evident. Inter‐hybrid distances for RFLP vs. pedigree data for 36 hybrids with known pedigrees showed a correlation of r = 0.87. Collective use of hybrids with similar RFLP profiles had an impact on diversity at least equivalent to that of some widely used hybrids. Multivariate techniques and diversity indices failed to show a reduction of diversity due to the high intensity of individual hybrid usage because extremely disproportionate usage among maize varieties was not evident. Restriction fragment length polymorphisms could provide assessments of the amount of diversity among commercially available hybrids.
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