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#MABC

2 public questions tagged with this topic.

Plant Breeding 4

Background selection in MABC helps in:

Background selection accelerates recovery of recurrent parent genome beyond theoretical expectation using genome-wide molecular markers distributed across all chromosomes. While foreground selection tracks donor gene, background selection scans chromosomes unlinked to target using polymorphic SSR or SNP markers distinguishing recurrent and donor alleles by size or sequence. In each backcross generation, individuals carrying target gene are genotyped across background, and those with highest proportion of recurrent parent alleles are chosen as parents for next backcross. Conventional backcrossing expects 87.5% recurrent by BC2F1, but background selection can achieve greater than 95% by BC2F1, reducing required backcross generations from six to three, saving 2-3 years and resource and cost. It also simultaneously reduces linkage drag around target by selecting for double recombination near donor interval using flanking markers called recombinant selection. Thus overall genome recovery is visualized through graphical genotype, minimizing donor remnants responsible for yield penalty and quality issues and accelerating variety development. Cost benefit analysis shows MABC reduces backcross generations from six to three, saving field seasons, labor, and land resources; simulation studies indicate background selection increases recurrent genome recovery rate by 15 to 20

Ref: Frisch M et al. 1999 Crop Sci – background selection for RPG recovery; Ribaut JM MAS strategies

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Plant Breeding 4

Foreground selection in MABC focuses on:

Marker-assisted backcrossing comprises two selection layers that accelerate recovery and ensure gene retention. Foreground selection focuses directly on target locus introgressed from donor, using gene-specific or tightly linked markers less than 2 cM to ensure presence of desired allele in each backcross generation. In early generations BC1F1, BC2F1, individual seedlings genotyped for foreground markers, carriers retained, non-carriers discarded, avoiding waiting for phenotypic expression that may require disease inoculation or recessive homozygosity assessment. This prevents accidental loss of target gene during backcrossing where without marker, gene may segregate 1:1 and be lost by chance. For recessive genes, codominant markers differentiate heterozygous carrier from homozygous recessive while phenotype cannot in heterozygous state. High-throughput PCR allows screening thousands of seedlings at seedling stage, accelerating introgression of genes like Sub1 for submergence, xa13 for bacterial blight, and crtRB1 for provitamin A. Foreground selection ensures high transmission of donor allele through backcross pedigree efficiently. Recombinant selection using flanking markers on both sides of target gene helps minimize donor segment length, breaking linkage drag by identifying double crossover events that retain small donor interval containing only beneficial allele while replacing surrounding chromatin with recurrent parent alleles during backcrossing generations for quality recovery.

Ref: Hospital F & Charcosset A 1997 Genetics – MABC foreground selection. Collard & Mackill marker review

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