Colchicine-induced abnormal meiotic chromosomal segregation in primary oocytes of the Chinese hamster. Part II. Anaphase lagging.

A single dose of 3/~g/g b.w. colchicine was intraperitoneally injected to female Chinese hamsters with a normal estrous cycle at the onset of the formation of the first meiotic spindle. Morphologically abnormal secondary oocytes having one or two extremely large first polar bodies occurred frequently, i.e., 47 (11.3~) out of 416 oocytes. In 30 of them, chromosome analysis was successful with both the oocytes and their giant polar body/bodies. In 25 cases, the abnormal chromosome segregation between the oocyte and its giant polar body/bodies could Ice ascertained. Three types of abnormal segregation were classified. One of them was of nondisjunction and the remaining two of anaphase lagging. ~[he fate of the lagging chromosomes was observed. They were included neither in the oocytes nor in their polar body, and eventually were degenerated within perivitelline space. The behavior and the fate of the lagging chromosomes and the mechanism of the giant polar body formation were discussed.