Search Results - (Author, Cooperation:L. H. Rieseberg)

2011-08-20

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Angiosperms/*genetics ; *Biological Evolution ; Diploidy ; *Extinction, Biological ; Ferns/*genetics ; *Genetic Speciation ; Genome, Plant ; *Polyploidy

1432-2242

Sunflower ; H. annuus ; Random amplified polymorphic DNA (RAPD) ; Introgression ; Plant breeding

Springer Online Journal Archives 1860-2000

Biology

Abstract Population genetic theory suggests that mating designs employing one or more generations of sib-crossing or selfing prior to backcrossing are more effective than backcrossing alone for moving alleles across linkage groups where effective recombination rates are low (e.g., chromosomally divergent linkages). To test this hypothesis, we analyzed the effects of chromosomal structural differences and mating designs on the frequency and genomic distribution of introgressed markers using the domesticated sunflower, Helianthus annuus, and one of its wild relatives, H. petiolaris, as the experimental system. We surveyed 170 progeny, representing the end products of three different mating designs (design I, P-F1-BC1-BC2-F2-F3; design II, P-F1-F2-BC1-BC2-F3; and design III, P-F1-F2-F3-BC1-BC2), for 197 parental RAPD markers of known genomic location. Comparison of observed patterns of introgression with expectations based on simulations of unrestricted introgression revealed that much of the genome was protected from introgression regardless of mating design or chromosomal structural differences. Although the simulations indicated that all markers should introgress into multiple individuals in each of the three mating designs, 20 of 58 (34%) markers from collinear linkage groups, and 112 of 139 (81%) markers from rearranged linkage groups did not introgress. In addition, the average size of introgressed fragments (12.2 cM) was less than half that predicted by theoretical models (26–33 cM). Both of these observations are consistent with strong selection against introgressed linkage blocks, particularly in chromosomally divergent linkages. Nonetheless, mating designs II and III, which employed one and two generations of sib-mating, respectively, prior to backcrossing, were significantly more effective at moving alleles across both collinear and rearranged linkages than mating design I, in which the backcross generations preceded sib-mating. Thus, breeding strategies that include sib-crossing, in combination with backcrossing, should significantly increase the effectiveness of gene transfer across complex genic or chromosomal sterility barriers.

Electronic Resource

1432-2242

Key words Sunflower ; H. annuus ; Random amplified polymorphic DNA (RAPD) ; Introgression ; Plant breeding

Springer Online Journal Archives 1860-2000

Biology

Abstract Population genetic theory suggests that mating designs employing one or more generations of sib-crossing or selfing prior to backcrossing are more effective than backcrossing alone for moving alleles across linkage groups where effective recombination rates are low (e.g., chromosomally divergent linkages). To test this hypothesis, we analyzed the effects of chromosomal structural differences and mating designs on the frequency and genomic distribution of introgressed markers using the domesticated sunflower, Helianthus annuus, and one of its wild relatives, H. petiolaris, as the experimental system. We surveyed 170 progeny, representing the end products of three different mating designs (design I, P-F1-BC1-BC2-F2- F3; design II, P-F1-F2-BC1-BC2-F3; and design III, P-F1-F2-F3-BC1-BC2), for 197 parental RAPD markers of known genomic location. Comparison of observed patterns of introgression with expectations based on simulations of unrestricted introgression revealed that much of the genome was protected from introgression regardless of mating design or chromosomal structural differences. Although the simulations indicated that all markers should introgress into multiple individuals in each of the three mating designs, 20 of 58 (34%) markers from collinear linkage groups, and 112 of 139 (81%) markers from rearranged linkage groups did not introgress. In addition, the average size of introgressed fragments (12.2 cM) was less than half that predicted by theoretical models (26–33 cM). Both of these observations are consistent with strong selection against introgressed linkage blocks, particularly in chromosomally divergent linkages. Nonetheless, mating designs II and III, which employed one and two generations of sib-mating, respectively, prior to backcrossing, were significantly more effective at moving alleles across both collinear and rearranged linkages than mating design I, in which the backcross generations preceded sib-mating. Thus, breeding strategies that include sib-crossing, in combination with backcrossing, should significantly increase the effectiveness of gene transfer across complex genic or chromosomal sterility barriers.

Electronic Resource

1432-2242

Key words RAPD ; DNA fingerprinting ; Homology ; Statistics ; Classification

Springer Online Journal Archives 1860-2000

Biology

Abstract  In order to estimate the impact of mis-coding non-homologous, co-migrating DNA bands as homologous, two sets of data were utilized. Analyses were conducted using three Helianthus species in which each co-migrating band had previously been confirmed. Comparisons of the similarities between these three Helianthus species using the original 177 RAPD bands and the corrected, homology verified, 197 RAPD band data set revealed that the triangular relationship among these three species was almost identical in both data sets. The non-homology errors in the Helianthanus data sets were found to be random. These random errors merely reduced the absolute similarities, but not the relative similarities nor the relationships among the taxa, in principal-coordinate-analysis ordination. Analyses of RAPDs for the classical Brassica U triangle were made by inserting random non-homologies for 5, 10, 15 and 20% of the original 220 RAPD bands. These analyses revealed a progressive decrease in similarities and less loading on the first two axes in principal coordinate analysis (PCO). However, the basic U triangle of relationships among these six Brassica species was maintained. It appears that if errors in homology of co-migrating DNA bands are random, this will have little effect on the relative similarities and on PCO ordination. This helps explain the successful use of RAPDs at the specific level.

Electronic Resource

1432-2242

Key words Gene flow ; Hybridization ; Sunflowers ; Transgenes

Springer Online Journal Archives 1860-2000

Biology

Abstract  The development of transgenic plants has heightened concern about the possible escape of genetically engineered material into the wild. Hybridization between crops and their wild relatives provides a mechanism by which this could occur. While hybridization has been documented between several crops and wild or weedy relatives, little is known about the persistence of cultivar genes in wild populations in the generations following hybridization. Wild and weedy sunflowers occur sympatrically with cultivated sunflowers throughout much of the cultivation range, and hybridization is known to occur. We surveyed two cultivar-specific RAPD markers in 2700 progeny in a naturally occurring population of wild Helianthus annuus over five generations following a single generation of hybridization with the cultivar. Moderate levels of gene flow were detected in the first generation (42% hybrids at the crop margin) and cultivar allele frequencies did not significantly decline over four subsequent generations. These results indicate that gene flow from cultivated into wild populations of sunflowers can result in the long-term establishment of cultivar alleles in wild populations. Furthermore, we conclude that neutral or favorable transgenes have the potential to escape and persist in wild sunflower populations.

Electronic Resource

1432-2242

Hybridization ; Gene flow ; Sunflowers Transgenes

Springer Online Journal Archives 1860-2000

Biology

Abstract With the development of transgenic crops, concern has been expressed regarding the possible escape of genetically-engineered genes via hybridization with wild relatives. This is a potential hazard for sunflowers because wild sunflowers occur as weeds in fields where cultivated sunflowers are grown and hybridization between them has been reported. In order to quantify the potential for gene escape, two experimental stands of sunflower cultivars were planted at two sites with different rainfall and altitude profiles. Populations of wild plants were planted at different distances from each cultivar stand. An allele homozygous in the cultivar (6Pgd-3-a), but absent in the wild populations, was used as a molecular marker to document the incidence and rate of gene escape from the cultivar into the wild populations of sunflowers. Three-thousand achenes were surveyed to determine the amount of gene flow from the cultivated to the wild populations. The marginal wild populations (3 m from the cultivar) showed the highest percentage (27%) of gene flow. Gene flow was found to decrease with distance; however, gene flow occurred up to distances of 1000 m from the source population. These data suggest that physical distance alone will be unlikely to prevent gene flow between cultivated and wild populations of sunflowers.

Electronic Resource

1615-6110

Angiosperms ; Datiscaceae ; Datisca ; Chloroplast DNA ; polymerase chain reaction ; restriction-site variation ; interspecific variation ; disjunct distributions ; biogeography

Springer Online Journal Archives 1860-2000

Biology

Abstract Datisca (Datiscaceae) is a ditypic genus with an intercontinentally disjunct distribution. Chloroplast DNA restriction site data was obtained from 23 populations and four 10–20 year old herbarium specimens ofD. glomerata and three populations ofD. cannabina from throughout their geographic ranges in western North America and southwest-central Asia, respectively. InD. glomerata, plastome diversity is partitioned geographically. All populations from southern California have a common plastome, while most populations north of this region share a relatively divergent plastome (0.49% sequence divergence). Likewise, these plastomes are highly divergent (0.87% mean sequence divergence) from those found inD. cannabina. Biogeographic processes dating to the Pleistocene and Late Miocene may be responsible for these intra- and interspecific patterns of chloroplast DNA divergence.

Electronic Resource