Abstract
Observations on meiosis in male Stenobothrus parallelus show that:-
1. Randomness of chiasma distribution is modified by “interference”; the mean frequency is more than five times the variance.
2. Randomness of chiasma frequency is modified by an indirect relationship to size such that while the long chromosomes are seven times the length of the short, they have only three times as many chiasmata. This is a genetic adaptation to secure regular pairing with a wide range of size of the chromosomes, and may occur in Drosophila.
3. In eight analysed cases the successive chiasmata were relatively “compensating ”.
4. Terminalisation in this species is slight. It consists merely in the expansion of loops at the expense of free arms and of the attachment loop at the expense of other loops. Considered in conjunction with similar studies on Tulipa, Campanula and other genera, these observations suggest an electrostatic explanation of terminalisation which is in accordance with the general behaviour of the chromosomes at these stages of their development.
We are indebted to Prof. J. B. S. HALDANE for criticism.
