|Lorenzen, Lisa - ISU|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 19, 1996
Publication Date: N/A
Interpretive Summary: Plant breeding programs carry out crosses between two desirable parents, followed by a few generations to allow segregation and assortment of gene combinations, and then by selection of improved cultivars. A long-standing question among plant breeders is how much recombination of genes takes place. That is, is the genetic makeup of the plant scrambled during breeding experiments or are huge segments of chromosomes carried through breeding programs relatively intact. We determined that some regions of some soybean chromosomes are inherited intact in many independent programs, while another region undergoes recombination much more often than one could expect by random chance. Results of this study suggest that breeding programs may select against recombination events to hold together desirable combinations of genes, or may select for recombinants in regions containing neutral or negative genes. This information will be of most use to those working to develop improved plant varieties.
Technical Abstract: A question often asked by plant breeders is whether recombination is maximized or minimized during the breeding process. A retrospective analysis of soybean cultivars was conducted to determine if cultivars are composed of large regions of chromosomes inherited intact from one parent (indicative of minimal recombination), or if the chromosomes are a mixture of one parent's DNA interspersed with the DNA from the other parent (indicative of maximal recombination). Twenty-six soybean cultivars and their immediate parents (47 genotypes) were analyzed at 89 RFLP loci to determine the minimal number and distribution of recombination events that could be detected. Cultivars derived from single cross and single backcross breeding programs showed an average of 5.5 and 7.8 recombination events per cultivar, respectively. An analysis of randomly dispersed independent regions of chromosomes indicated that the number of recombination events did not differ statistically from what was expected at random. However, detailed analysis of each linkage group revealed that large portions of linkage groups "D", "F", and "G" were inherited intact from one parent in several cultivars. A portion of linkage group "G", in contrast showed more recombination events that expected, based on genetic distance. This analysis suggests that the breeding process acts to select against recombination events where agronomically favorable combinations of alleles are present in one parent, and for recombination in areas where agronomically favorable combinations of alleles are not present in either parent.