RILs are developed by:
Recombinant Inbred Lines are immortal homozygous mapping population developed by repeatedly selfing progeny from single cross through single seed descent without selection for six to eight generations. Starting from F2, one seed per plant is advanced randomly; heterozygosity halves each generation, approaching 99% homozygosity by F6, genotype fixed as mixture of parental alleles in homozygous form through recombination. Each RIL represents unique mosaic of parental chromosomes after multiple recombination events, capturing increased mapping resolution compared to F2 due to accumulated crossovers. Because RILs are true-breeding, they can be multiplied and evaluated across environments, years, and labs for accurate phenotyping of quantitative traits with replication. Genetic map constructed from segregation of codominant markers in RILs enables QTL detection with reduced dominance variance and greater additive estimation. RIL population is cornerstone for fine mapping, gene cloning, and multi-environment trial in Arabidopsis, rice, and maize for complex trait dissection. Advances in genotyping by sequencing and SNP arrays provide high density maps improving RIL utility for ultra high resolution mapping and genome wide association; immortal nature allows sharing seeds among researchers globally, enabling collaborative multi-environment QTL validation and identification of stable QTLs useful for marker assisted breeding across regions.
Ref: Burr & Burr 1991 RIL development; Singh & Singh Plant Breeding – SSD repeated selfing method