Introgressing multiple QTL in breeding programmes of limited size

Area of Science:

• Animal Breeding and Genetics
• Quantitative Genetics
• Genomic Selection

Background:

• Marker-assisted introgression (MAI) is a valuable tool for genetic improvement in livestock and crops.
• Efficiently introgressing multiple quantitative trait loci (QTL) from a donor breed into a recipient breed, especially in small populations, presents challenges.

Purpose of the Study:

• To evaluate the feasibility of enriching a breed with favorable alleles from multiple unlinked QTL using MAI in small populations.
• To assess the impact of selection proportion, marker interval size, number of QTL, and QTL position uncertainty on introgression success.

Main Methods:

• Simulated marker-assisted introgression over five generations of backcrossing and five generations of intercrossing.
• Utilized informative flanking markers to select progeny with the highest expected number of donor QTL alleles.
• Analyzed the effects of varying selection fractions (5-20%), marker interval sizes (5-20 cM), and the number of introgressed QTL (three to five).

Main Results:

• Sufficient QTL frequencies (0.30-0.35) were maintained after five backcrossing generations, even with 20% selection and three QTL.
• Over 90% of individuals achieved homozygosity for all introgressed QTL after five intercrossing generations.
• Higher selection proportions and more QTL increased the number of intercrossing generations needed for fixation.

Conclusions:

• Marker-assisted introgression of multiple QTL is feasible in small populations without requiring all selected individuals to carry favorable alleles at every locus during backcrossing.
• The strategy allows for successful enrichment of breeds with desired genetic traits through targeted introgression.