Nature 189, 683 - 684 (25 February 1961); doi:10.1038/189683a0

The Pachytene Stage in Mammalian Oocytes

B. M. SLIZYNSKI

Institute of Animal Genetics, Medical Research Council Induced Mutagenesis Group, Edinburgh.

SEVERAL chromosomal abnormalities have recently been described in human cytogeneties, some of them probably directly and causally related to certain phenotypical effects. All this work was carried out using chromosomes of the mitotic metaphase, mostly from cultures of various cells. The exact identification of any single chromosome is not possible. All 42 autosomes and a pair of sex chromosomes are divided into four or five morphological classes using the length of arms and the position of the centromere as a landmark of identification. The difficulties may be illustrated by the fact that the sex of an individual is determined as male if there is an uneven number of small chromosomes. There is a great need for a more precise method of identification by which individual chromosomes can be recognized.