Determination of n+1 Gamete Transmission Rate of Trisomics and Location of Gene Controlling 2n Gamete Formation in Chinese Cabbage (Brassica rapa)

A set of trisomics of Chinese cabbage was used for determining the n+1 gamete transmission rate and locating the gene controlling 2n gamete formation on the corresponding chromosome. The results showed that the transmission rates of extra chromosomes in different trisomica varied from 0% to 15.38% by male gametes and from 0% to 17.39% by female gametes. Of the nine F2 populations derived from the hybridizations between each triaomic and Bp058 (2n gamete material), only Tri-4×Bp058 showed that the segregation ratio of plants without 2n gamete formation to plants with 2n gamete formation was 10.38:1, which fitted the expected segregation ratio of the trisomics (AAa) based on the 7.37% of n+1 gamete transmission through female and 5.88% through male. In other populations the segregation ratios varied from 2.48:1 to 3.72:1, which fitted the expected 3:1 segregation ratio of the bisomice (Aa). These results suggested that the gene controlling 2n gamete formation in Chinese cabbage Bp058 was located on chromosome 4. Further trisomic analysis based on the chromosome segregation and the incomplete stochastic chromatid segregation indicated that the gene locus was tightly linked to the centromere.