GENELIST: The accompanying table lists the defined and designated gene loci of maize. The table includes the symbol for the locus, the chromosome (L=long arm, S=short arm) and map location, name and a brief phenotypic description, availability from the Stock Center (S), photograph (P) in Mutants of Maize (Neuffer et al. 1968), and references to original descriptions. Stocks may be obtained from the Maize Genetics Stock Center (see the preceding section); other variants (e.g., isozymes and RFLPs) exist inherently among generally available strains.

For a table of mapped RFLP loci, see MNL 65:145-153.

Three enhancements of the resources for maize genetics research are currently under development: The Maize Handbook (Freeling and Walbot, eds., Springer-Verlag, fall 1992); Mutants of Maize (Neuffer, Coe, and Wessler, Cold Spring Harbor Lab., 1993); and the Maize Database, Maizedb (Plant Genome Initiative, 1993 projected on-line date; please see the following section).

NOMENCLATURE: New definitions of standards and criteria are in preparation and will be distributed as soon as they are completed.

MAPS: Our working maps follow the table. The traditional linkage map, based on recombinational analyses of Mendelizing variations in an expression or a gene product, is in the center. Each map represents the order and distances in centimorgans (1% recombination = 1 cM), for loci for which sufficient information is available to make a reasonable judgment of location. Each chromosome begins at the top with the most distal locus known in the short arm. The physical (cytological) map of each chromosome, immediately to the left of each linkage map, is drawn with the length of each arm in proportion. Locations of B-A translocations, which generate hemizygous segments, are shown as TB-..., and A-A translocations as T with chromosome numbers and identifiers (see MNL 55:140ff.); placement on the physical map is in accordance with observed breakpoints; placement on the linkage map is in relation to cytogenetic mapping data (see MNL 52:129ff., 59:159ff., 60:149ff.). Locations of the centromeres are indicated according to the best available data from cytogenetic studies. The vertical line associated with simple B-A translocations represents the segment within which the breakpoint is located (genes distal to the line on that arm should be uncovered). In the case of compound translocations, the associated vertical line on the linkage map for the first arm involved (e.g., 1L of TB-1La-5S8041) defines the segment within which the second breakpoint is located (genes distal to the line are not uncovered). On the map of the second arm involved (5S in the example), genes distal to the associated line are uncovered (as they are with simple B-A translocations). TB's shown spanning one or more genes may or may not uncover the indicated gene or genes. To the right of the linkage map are shown genes (alphabetically in groups) for which a "rough" placement has been defined, either near a gene already on the map or to a region of the map. Furthest to the right are shown genes placed only to chromosome (vertical line with arrows) or to one arm (vertical line from near the centromere to the end of the arm).

To the left of each physical map is a map showing RFLP and isozyme loci, representing information and data derived at Missouri and at Brookhaven supplemented with information provided by Pioneer, Agrigenetics, and others. This is a strictly approximate representation, designed to aid searching and comparisons; it is NOT a mutually interdigitated map. The several available RFLP maps, most of which are internally consistent, are largely but not completely consistent with each other. Construction of an integrated map requires systematic compilations of data, but more importantly the development of complex mapping engines that are not yet available in any form. Enhanced mapping engines are a target of some labs, including the Maizedb program, and may become available to apply to our data during the coming year.

Dashed lines tying the RFLP map to the linkage maps show approximate locations of gene loci. Positions shown are mutually interdependent (i.e., locations indicated are derived from the information from each source by circular logic ).

The current Plastid Chromosome Genetic Map, prepared by Steve Rodermel, follows the nuclear working maps. For the Mitochondrial Map, see MNL 64:165.

MAP IT: The importance of placing loci defined by probes of known function cannot be overstressed. In a number of cases these give very accurate ties to the conventional map and, in the very least, provide functional significance to a particular region of the genome that will be important as further additional studies (particularly in the area of quantitative genetics) progress. Therefore, if you have a clone for a known function and know or believe that it hybridizes to a maize genomic sequence, please attempt to map the locus (or loci). This can be accomplished in a couple of ways (and we recommend doing both). First, the set of recombinant inbreds should be probed and the data sent to Ben Burr for analysis. Second, it would be appreciated if the probe could be sent to Missouri for mapping in the Immortal F2 population. We would also use the probe in correlation to physical and conventional markers. We have included in this Newsletter a sample form of the desired information for each clone you provide. If you have any questions regarding mapping of RFLP loci (both old and new), please call or write.

The quality of these resources is enhanced each year by corrections, clarifications, and suggestions provided by Cooperators; your input is welcome and needed.

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