Chromosome Pairing in Melanoplus femur-rubrum

Abstract

The individual chromatids were traced through chiasmata in chromosome configurations during all stages of the first meiotie division in Melanoplus femur-rubrum.
Seventy-one compensating and thirty-five non-compensating chiasmata were found. The chiasma frequencies Show interference curves of variation. There is therefore both “chromatid interference” and “chiasma interference” in this species.
There is no significant reduction of chiasma frequency in the long chromosomes, and none in the medium and short ones. Interlocked and non-interlocked chromatids occur with equal frequency in the compensating chiasmata. These observations are opposed to Sax's hypothesis of crossing-over; they are in accord with the general “partial chiasmatype” hypothesis, but Belling's formulation of it would require modification to account for the preponderance of compensating chiasmata in this species.
Terminal chiasmata are demonstrated to arise from earlier interstitial ones. From both direct observation and the calculation of terminalization coefficients, the movement of chiasmata was found to be toward the spindle attachment in some cases.
There is an indirect relationship between chiasma frequency and length of chromosome, and also between length of chromosome and time of terminalization.
A heteromorphic bivalent was found in one indi'vidual. It has only one chiasma and separates equationally in the first division, as would be expected an the “partial chiasmatype” hypothesis.
A greater degree of contraction was found in the chromosomes of the spermatogonial divisions than in the first division of meiosis, and the different types of chromosomes contract differentially.