Study On Factors Affecting The Efficiency Of Marker-Assisted Introgression

In animal breeding, we often meet such problem: a breed or line with many superior traits while at the same time it exist some objection, so influence its economic value. Marker-assisted introgression makes the problem simple. During the marker-assisted introgression process in practical breeding, the genetic background of recipient need not restore entirely, but some certain background traits need restore, the markers closely linked with QTLs related to these traits and the phenotypic information can be used to make MBLUP background selection so that the genetic background could restore. In this study, MBLUP was first used for genetic background restoration, analyzing the effect of different factors on marker-assisted introgression efficiency, discussing the suitable marker-assisted introgression scheme.The effect of different factors on the efficiency of marker-assisted introgression a QTL was simulated in this study. The factors include different foreground selection methods (single marker selection, flanking markers selection and direct gene selection), background selection methods (no selection-NO, phenotypic selection-PH, BLUP selection, MBLUP selection, markers score selection-MS, genomic similarity selection-GS and marker index selection-MIS), map distances between markers (2cM, 5cM, 10cM, 20cM and 30cM), population sizes (500, 800 and 1000), sire-dam ratios (1:5, 1:8 and 1:10), trait heritabilities (low, middle and high), genotypic values of QTL (low, middle, high), original marker allele frequencies (0.5/0.5, 0.6/0.4, 0.7/0.3, 0.8/0.2, 0.9/0.1 and 0.95/0.05).The following results were obtained: (1) When introgress a known QTL, direct gene selection can make the QTL retain during marker-assisted introgression, when introgress a unknown QTL, the flanking markers selection can get higher introgressed QTL frequencies and more genetic responses for foreground trait than single marker selection. (2) MS, GS and MIS can make recipient genome recover entirely through 3~4 backcross generations, though MBLUP selection could not make recipient genome recover quickly, it can recover the QTL frequencies and get the most genetic responses for recipient background traits. (3) Shortening map distances between markers can increase introgressed QTL frequencies and genetic responses for foreground traits, but when the map distances shorten from 1 OcM to 2cM, the change range of introgressed QTL frequencies is little. (4) Enlarging population sizes and sire-dam ratios can increase introgressed QTL frequencies and genetic responses for foreground traits. (5) Increasing foreground trait heritabilities and genotypic value of QTL can heighten genetic responses for foreground traits, but has little effect on introgressed QTL frequencies and genetic background restoration. (6) When use flanking markers selection for foreground selection, enlarge the original marker allele frequency of donor can increase introgressed QTL frequencies and genetic responses for foreground traits. (7) When use MBLUP selection for foreground selection, enlarge the original marker allele frequency of donor can increase background QTL frequency and genetic responses for background traits, but has no effect on introgressed QTL frequencies and genetic responses for foreground traits. (8) When the original marker allele frequency of donor line is 0.8, useMBLUP selection for foreground selection, increase the foreground selection proportions, can decrease introgressed QTL frequencies and genetic responses for foreground traits.The effect of different factors on the efficiency of marker-assisted introgression two QTLs was further simulated. The factors include different experiment designs (experiment design 1 and experiment design 2), population sizes (500, 800 and 1000), foreground selection methods (flanking markers selection and MBLUP selection).The results indicate that: (1) For the two experiment designs, during backcross phase, experiment design 2 obtained a little higher introgressed QTL frequencies than design 1, during intercrossing phase, there is no diff...