Chromosome evolution in wild populations of acrididæ Part I. On the occurrence of a supernumerary chromosome in Aiolopus sp.

Abstract

1. Two individuals out of a total of 26 specimens ofAiolopus sp. 'B' examined cytologically showed in all the dividing cells of their testes a super-numerary chromosome of about one-third of the size of the X. 2. The normal diploid number in the species is 23 and it has an XX-XO mechanism of sex-determination. 3. The additional chromosome never forms a chiasma with any member of the normal chromosome set, but it has been found, in about half of the diplotene and diakinesis nuclei, to be associated with the X chromosome. 4. The supernumerary chromosome segregates without division independently of the X in the first meiotic division and divides equationally at the second meiotic division. As a consequence of this behaviour, it is regularly included in half of the sperms produced.