Cytological and Cytogenetic Maps

Tomato aneuploid stocks have been used as tools for mapping loci for many decades (Lesley 1932). Populations developed from crosses between irradiated and mutant cultivars were extensively used to generate chromosome-based maps of tomato in the 1960s (Khush and Rick 1967b, 1968a, b) (Table 7, map 1). Radiation-induced chromosomal deficiencies allowed expression of recessive mutant alleles and localized mutations to chromosomal arms. In the 1990s, a resurgence of interest in cytology prompted the development of a physical recombination map used to quantify the distribution of crossovers along each chromosome (Sherman and Stack 1995) (Table 7, map 2). In the same decade a variety of in situ hybridization maps were also developed, linking fluorescent genetic markers to their physical chromosomal location (Fuchs et al. 1996; Zhong et al. 1996; Peterson etal. 1999; Wang etal. 2006), (Table 7, maps 3-7). These are termed cytogenetic maps, due to the connection made between genetic linkage and cyto-logical position (Harper and Cande 2000). The linear order of markers is not always conserved between genetic and cytological positions (Peterson etal. 1999).

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