THE STRANDEDNESS OF MEIOTIC CHROMOSOMES FROM ONCOPELTUS

Abstract

Meiotic chromosomes were isolated from male Oncopeltus fasciatus by dissecting the testes under insect Ringer's solution and spreading the living cells on the Langmuir trough. After being dried by the critical point method, preparations were examined under the electron microscope. Chromosomes at all stages of prophase prove to be multistranded. A significant increase in the number of parallel 250 A fibers in the chromosomes occurs between zygotene and diakinesis. Parallel folding, rather than true multistrandedness, is interpreted as the mechanism responsible for this observed increase in multistrandedness. It has not been possible to determine whether the multistrandedness observed at leptotene represents true multistrandedness or is the result of parallel folding. Apparent multistrandedness is lost at metaphase when the 250 A fibers of the chromosomes become coiled more tightly. In preparations isolated by these methods, no structures other than the 250 A chromosome fibers are visible in the chromomeres, which appear as regionally coiled or folded areas of the fibers along the arm of the chromosome.

The Human Chromosome

“…This explanation is supported by our observation that gentle loosening of the condensed metaphase chromosomes by protease treatment seems to uncover underlying parallel fibers . Wolfe and Hewitt (40) have also reported that Oncopeltus meiotic chromosomes exhibit parallel fibers while extended in prophase I, but not when they are more condensed in metaphase I .…”

Observations on the Cytology and Fine Structure of Mitosis in the Fern, <i>Ophioglossum petiolatum</i> Hook

“…Some evidence of chromosome coiling could thus be observed. However, it seems apparent that the most informative data concerning chromosome structure will come from whole mount studies of isolated chromosomes (Wolfe 1965, DuPraw 1966, Govaerts and Dekegel 1966, Rae 1966, Wolfe and Hewitt 1966 microtubules comprising the spindle fibers are similar to those previously described for plant spindles (Ledbetter and Porter 1963, 1964, Pickett-Heaps and Northcote 1966.…”

The Fine Structure of Human Somatic Chromosomes Studied by Scanning Electron Microscopy and the Replica Method

“…The surface-spread technique has merely made clear that the DUPRAW, 1965 a, b;WOLFE and BERNARD, 1965;WOLFE and HEWITT, 1966).…”