Linkage analysis and genetic mapping Marker assisted selection and “map-based” breeding “Mendelizing” QTL

“Mendelizing QTL”

We can more completely characterize quantitative traits and the loci that confer quantitative inheritance Identify the number of loci conferring a Quant. Trait Identify gene action and estimate the magnitude of individual loci (VQTL/Vp) Select for genotype when phenotypic selection is less efficient

New technology opens the possibility of “map-based” breeding. How easy will it be to pyramid genes or break unfavorable linkage?

Synthesize information from numerous crosses to understand patterns of genome organization Clusters of disease resistance genes Candidate genes for Quant. Trait loci

Power of modern genetic mapping in breeding applications comes from: Combining classical and new techniques Placing “economic traits” onto maps Working in genetic backgrounds that favor application

Building Genetic Maps Single-locus analysis Two-locus analysis Measuring linkage distance Linkage grouping Gene ordering Multi-point analysis

Building Genetic Maps Single-locus analysis Two-locus analysis Measuring linkage distance Linkage grouping Gene ordering Multi-point analysis

Definition of Genetic Linkage The association of genes located on the same chromosome The association or non-independence among alleles at more than one locus Statistical definition

Linkage between qualitative traits Does each locus segregate as expected? Mendel’s first law Do the loci assort independently? Mendel’s second law What is the distance between loci?

Estimation of linkage distance Historical overview Additive method Weighted mean method Product method Maximum likelihood Log of the odds

Keep in mind the following: We are first going to cover the theory and practice of linkage analysis Application of linkage data and “map-based” breeding are up to the creativity of the breeder There are sometimes conflicting goals between breeding applications and genetic applications