Über Die Feinstruktur Des Genoms Im Bereich Eines Pab Locus Von Neurospora Crassa

Summary

In crosses involving three allelic pab markers of the same cistron, the recombination frequencies between any two of the markers were such, that a consistent order of the three markers could be established. In these crosses two closely linked markers (0,9% distance, on each side) were also present. The segregation of the pab independent types showed, with respect to the outside markers, a frequent appearance of all four types of outside marker combinations, which in the crossing-over theory would belong to one crossover between the pab markers and 0, 1, or 2 crossovers in the adjacent regions. This deviation from ordinary crossingover expectations, called correlation effect, is confined to very small dimensions of the genome. In the present case to regions of about 0,05% map units.-Inspite of this effect, which sometimes nearly equals out the four types of outside marker combinations, the two recombinant types were, in all present crosses, significantly different, such that the pab markers could be ordered with respect to the outside markers. This ordering is in agreement with that established independently from recombination frequencies. Thus the frequencies of the different types of outside marker combinations are in agreement with the assumption, that the linear genes are built lengthwise into the chromosomal thread, and in disagreement with the assumption that genes or even larger chromosomal parts are sidechains of the chromosome.

For this work a subdividing technique has been used by which it was relatively easy to obtain the double mutants between close markers. The same technique can also be applied for the partial selection of double mutants of allelic markers, provided that relatively close markers are available. In determining the linkage relationships it has been found, that me-3 seems to involve a fairly large deletion.