Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/15/2003
Publication Date: 2/15/2003
Citation: Zou, J., Lee, J., Singh, R., Xu, S.S., Cregan, P.B., Hymowitz, T. 2003. Assignment of molecular linkage groups to the soybean chromosomes by primary trisomics.. Theoretical and Applied Genetics. Vol. 107:745-750. Interpretive Summary: Soybean is a major U.S. crop that is grown on 70 million acres. A more complete knowledge of the soybean genome and the structure of its chromosomes are needed to assist in making further genetic improvements of the soybean. A trisomic individual is one that has a normal set of chromosome pairs plus a third copy of one chromosome. Humans with Down's Syndrome are trisomic for chromosome 21. Trisomic plants have been studied for many years in corn and tomato. Any gene that is located on the trisomic chromosome will be inherited in an unusual fashion, that is, the rules established by Gregor Mendel will not apply. Thus, trisomic plants can be used to associate a particular gene or DNA marker with a particular trisomic chromosome. In soybean, a set of trisomic individuals has been completed. Each member of the set of 20 soybean trisomics is trisomic for a different chromosome. A new genetic map of the soybean was recently developed that has more than 2000 DNA markers or landmarks that are divided into 20 groups referred to as linkage groups. The 20 linkage groups are assumed to correspond to the 20 soybean chromosomes. We report here the assignment of 11 linkage groups to the 11 chromosomes upon which they reside using a procedure referred to as trisomic analysis. This procedure used the simple sequence repeat DNA markers on the new map of the soybean genome to rapidly detect deviations from normal inheritance patterns in genetic populations developed from the soybean trisomics. The knowledge gained through this work allows soybean geneticists to better understand the structure of the soybean genome and the physical organization of the genes in the genome. This knowledge will facilitate breeding of superior soybean varieties.
Technical Abstract: Primary trisomics provide an invaluable cytogenetic tool to locate genes and to associate linkage groups with specific chromosomes. We have assigned 11 molecular linkage groups to soybean [Glycine max (L.) Merr., 2n=40] chromosomes by using primary trisomics (2x + 1 = 41) and SSR markers. Primary trisomics were hybridized with G. soja Sieb and Zucc. (2n = 40) in the greenhouse, F1 plants with 2n = 40 and 41 were identified cytologically and 41 chromosome plants were selfed. The SSR markers usually segregate in a co-dominant (1:2:1) fashion in the F2 population. A deviation from 1:2:1 ration suggests association of the markers with a particular chromosome. Of the possible 220 combinations, involving 20 molecular linkage groups and 11 primary trisomics, 151 combinations were examined. The relationships between soybean chromosomes and molecular linkage groups are: 1=D1a+q, 3=N, 5=A1, 8=A2, 9=K, 13=F, 14=C1, 17=D2, 18=G, 19=L and 20=I. These results provide a unified view of the available cytogenetic, classical, and molecular mapping information in soybean.