Factors Affected BC1F1 Size for Development of Genome-Wide Introgression Lines

Introgression lines are important genetic materials for genetics study and breeding. Development of those lines involves cross and backcross processes between recipient and donor parents. The population size of BC₁F₁ is a critical parameter for fully covering donor genome and successfully obtaining desired introgression lines. However, the minimum sufficient number of BC₁F₁ plants is unknown for each species and cannot be obtained experimentally. A computer program was developed by simulating the recombination process during meiosis to define the ideal BC₁F₁ population size. The reliability of the program was confirmed by mathematics and experimental data. Three factors including linkage group number, linkage group length, and gene density were analyzed, and all of them had positive relation with the size of BC₁F₁ population. The population size increased from 6.06 to 9.49 when the linkage number increased from 5 to 40. The population size was 7.14 when the linkage group length was 80 cM, while it became 8.64 when the length was 200 cM. The population size was 7.65 with the density of 20 cM per gene and 8.22 with 10 cM per gene. The BC₁F₁ population sizes of rice (Oryza sativa L.), wheat (Triticum aestivum L.), maize (Zea mays L.), and soybean (Glycine max L. Merr.) were predicted to be 12, 13, 14–15, and 13, respectively, by the program with 95% confidential level.