Efficiency of I-factors in offspring of isogenic lines of Drosophila melanogaster

Genetics of inbred Drosophila melanogaster. XXV. Simultaneous tests of I-inductivity and M-type

From a branch of an inbred line of Drosophila melanogaster we introduced the genome into cytoplasms from various sources. Among a pair of sister-lines, which at first showed R-type in the I-R system, one line switched to I-type. From a branch of this I-type line, for several generations kept at 18 degrees C, we established sub-lines derived from four single females. They were propagated at 25 degrees C with 14 or 28-day generation interval, respectively. It was presumed that 14-day generation interval gave strong, and 28 days interval gave weak R-elements. Tests of the strength of the I-inductivity disclosed no relation to the assumed strength of the R-elements. By the same test technique, primary non-disjunction and chromosome loss, the M-type was studied in the eight sub-lines. There appeared diversities in the M-type, assumed to be related to chromosomal mutations. Both primary non-disjunction and chromosome loss were affected by the P-M reaction.

Variation in the strength of R-reactivity and I-inductivity in inbred lines of Drosophila melanogaster

Two sets of two sister lines of Drosophila melanogaster, with common genome and cytoplasms of different origin, originally showed intermediate R-effects. All four lines had been kept at constant protocol for about 150 generations. From each of the four lines three sublines were established from single females and the strength of R-reactivity was tested by chromosomal loss technique. In two of the four sets, there was heterogeneity between the sublines. One subline in both cases was similar to the three sublines from the sister lines. The remaining two sets remained unchanged. Specific reactions were found in particular combinations of R- and I-lines. Six sets of independently arising I-lines with K-genome showed different response in the strength of their I-inductivity. The evolutionary relation in the strength of R-reactivity of R-type lines and the implication of the specific reactions are discussed.