Jump ahead to any of the linkage groups:

Linkage group I
Linkage group II
Linkage group III
Linkage group IV
Linkage group V
Linkage group VI
Linkage group VII

Genetic linkage information on chromosomal loci is summarized in Fig. 1 through 7. Loci whose order is established with reasonable certainty are displayed on the maps. Many loci are not displayed, but are listed below the maps because their order has not been completely established relative to loci shown on the map. The meaning of each locus symbol, data on linkage with nearby markers, and further detailed information will be found in the section Information on Individual Loci, where genes are listed alphabetically by symbol.

Relative distances on the maps are only rough approximations. rec genes with local effects differ in many of the strains used for mapping, and recombination values for the same interval have been shown to vary 10-fold or more in crosses of different parentage (167, 169, 170, 174). For this reason, no attempt has been made to correct for undetected multiple crossovers in long intervals by using a mapping function.

Linkage group I is estimated to be at least 200 map units long, and the total for all seven groups probably exceeds 1,000 (808). Because of the genetically determined variability, no map scale is indicated graphically. Interval lengths were estimated as composite or representative values based on all the crosses available and are shown on the scale ca. 1 cm = 7% recombination. It must be stressed that absolute and relative interval lengths shown on the maps possess only limited predictive value, depending on the genotype of a particular cross with respect to genes that determine the frequency of recombination in each local region. In contrast, gene order is constant in the absence of rearrangement.

Because of rec gene differences, gene order cannot be established reliably by combining two-point recombination values from different crosses. Seriation has, therefore, been based wherever possible either on meiotic crossing over data from three-point crosses or on duplication coverage. Duplication-producing rearrangements such as insertional or terminal translocations allow a simple test to be performed from which it can be determined whether a locus is to the right or left of a rearrangement breakpoint (see, for example, references 798, 808, and 816). Breakpoints are shown on the maps only for those rearrangements that have been used to establish gene order or to map chromosome tips and centromeres.

Crosses involving strains with a history of transformation have not been used in constructing standard maps because genes may be inserted in abnormal positions, and we recommend that new loci not be defined on the basis of mutations that originated in pedigrees from transformed parents until more is understood about the transformation process. (See the entry for os-6.)

Fig. 1. Linkage group I of N. crassa. The map shows loci whose order is established with reasonable certainty. Order of markers in parentheses is uncertain. The centromere is represented as a circle. The order of genes listed below the map is less well established relative to loci shown on the map; percentages and fractions indicate recombination among random ascospore progeny, unless stated otherwise. For detailed information and documentation, see alphabetical entries under "Information on Individual Loci."


FIG. 2. Linkage group II of N. crassa. Scale and conventions as for Fig. 1.