Maize NAM map as downloaded from the Panzea website.

From the Panzea FAQ: Our collection of 5000 RILs in 25 populations (plus the pre-existing IBM RIL population derived from a cross of B73 and Mo17) is collectively referred to as our "maize Nested Association Mapping (NAM) population". NAM is a new approach to the mapping of genes underlying complex traits, in which the statistical power of QTL mapping is combined with the high (potentially gene-level) chromosomal resolution of association mapping. The RILs are "nested" in the sense that they all share a common parent, B73, but each population has a different alternate parent. The NAM strategy consists of genotyping a feasible number of (e.g., about 1000-2000) common parent specific SNPs in the entire mapping population, in combination with much higher resolution genotyping of the 26 parents (e.g., by sequencing the entire genome of all 26 parents). The common parent specific SNPs are either present only in B73 or are present in B73 and rare in the other parents. These are used to classify each chromosomal segment that they define in each RIL according to whether it derives from B73 or from the corresponding alternate parent. In this manner, the high resolution genotypic sequence data can be projected from the parents onto the RIL offspring, without the need to sequence all the offspring. An association analysis can then be performed across the entire population. This takes advantage of historical recombination in the ancestors of the 26 parents in order to map the genes responsible for a given trait, potentially down to gene-level resolution. The NAM concept is further explained and demonstrated via computer simulation in Yu et al. (2008).