Abstract

A single individual of Moraba scurra from Michelago, N.S.W. (out of 1730 examined cytologically) was found to be heterozygous for a pericentric inversion, which has converted the normally equal-armed AB chromosome into a J-shaped element with one limb about twice the length of the other. This is presumably a newly arisen rearrangement. It leads to five detectable cytogenetic consequences: (1) a decline in the chiasma frequency of the AB bivalent; (2) occasional failure of pairing, there being two AB univalents at first metaphase; (3) frequent orientation of the AB bivalent with its centromeres on the equator instead of in the axial plane; (4) frequent formation of a chiasma between the mutually inverted sections; (5) a stimulatory effect on the chiasma frequency of the short arm of the CD chromosome carrying the Blundell inversion. The implications of these findings for the chromosomal evolution of the approximately 180 known species of morabine grasshoppers are indicated.