The non-random chromosome segregation in spermatocytes of Gryllotalpa hexadactyla. A micromanipulation analysis.

Abstract

Males of Gryllotalpa hexadactyla have 22 autosomes and one X chromosome in their chromosome complement. One pair of autosomes forms a heteromorphic bivalent in meiosis: one dyad is several times the size of the other. At metaphase of the first meiotic division the large dyad and the X chromosome are invariably oriented to the same pole, and they move to this pole in anaphase. These earlier observations (Payne, White) have been confirmed by studies on living spermatocytes, and a preliminary experimental analysis by micromanipulation has been made. No physical connection between the X chromosome and the heteromorphic bivalent could be detected when either one was moved with a microneedle. When the X chromosome was detached from the spindle in prometaphase and brought to the other pole, it oriented to this pole, but it usually reoriented and moved back to the original pole. When the heteromorphic bivalent was detached from the spindle and its position inverted, the large and the small dyads oriented to the new poles. The heteromorph remained in inverted position but the X chromosome usually reoriented and moved to the pole to which the large dyad was now oriented. When the heteromorph was detached and taken out of the cell, the X chromosome reoriented and moved to the other pole, reoriented again and moved back to the original pole. When the X chromosome was detached and taken out of the cell the heteromorph did not show any reaction. It is concluded that the X chromosome's reorientation response is the critical factor in non-random segregation in Gryllotalpa.