Published online by Cambridge University Press: 14 April 2009
Recessive transformants (col) obtained from v (vermilion) embryos treated with v+ DNA are shown to map at 1−0·02, a position not distinguishable from that of su(s) (suppressor-of-sable) and in agreement with observations indicating phenotypic allelism of col with su(s) mutants. Recombination in the y–col–gt segment of the X chromosome, over a total map length of O·3 units, was studied among the progeny of colv1/y1gtE6cvv1f and y1colgtE6cvv1f/v1 females. The data from both crosses exhibit the following features: (1) recovery of reciprocal recombinants between y1 and col; (2) recovery of reciprocal recombinants between col and gtE6 and (3) striking negative interference in the y–col–gt segment. These results allow three alternative interpretations: (1) that recombination in the y–col–gt segment results from conventional crossing-over, with high coincidence of crossovers in the two subsegments; (2) that it results from symmetrical gene conversion at the col site (col to col+, and col+ to col), which may be accompanied by single cross-overs in either of the adjacent regions; (3) that col behaves like a transposable element, formally symbolized su(s)+·col, and that recombination in su(s)+·col/su(s)+ (i.e. col/col+) heterozygotes results from transposition of the col element from homolog to homolog, accompanied sometimes by crossing-over, either in the y–col subsegment or in the col-gt subsegment.