Figure 1

The various kinds of analysis that are being applied to the wheat genome. (a) Markers such as single nucleotide polymorphisms (SNPs) and simple-sequence repeats (SSRs) are used in meiotic mapping to narrow down a complex trait to a region of a chromosome. (b) ESTs are used to discover new candidate genes within the chromosomal region of interest, and their expression is analyzed using microarrays and other techniques. (c) The ESTs are mapped onto the clones that make up a physical map of the genome. (d) Allelic diversity, such as the variable-length repeat markers linked to a gene (upper box) and/or SNPs or point mutations inside or outside the gene itself (lower box), can be used for mapping; mutations can be produced using mutagenesis, including using 'target-induced local lesions in genomes' (TILLING, a technique that creates point mutations through chemical mutagenesis and then screens for lesions using high-throughput genotyping methods). (e) Linkage disequilibrium (LD) mapping and mapping of the association of markers with the phenotype or quantitative trait of interest can then be used to identify the gene responsible for the trait.