Population cytogenetics of Chorthippus vagans. I. Polymorphisms for pericentric inversion and for heterochromatin deletion

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Abstract
Two different polymorphisms have been identified in natural populations of the grasshopper Chorthippus vagans. One of these involved an inversion polymorphism in the M7 chromosome and was present in two populations from Granada. In one of these, from Prados del Pinar, the frequency of this polymorphism was constant over three consecutive generations, and meiotic studies of heterozygous individuals indicated that this inversion had no effect on male fertility. The second polymorphism involved a deletion of the distal C-band of the short arm of the M4 chromosome, which was observed in three different populations. From the observed difference between its frequency in adults and embryos in one of these populations, that of Prados del Pinar, it would appear that this deletion is strongly selected against. Despite this, its frequency was maintained in adult individuals of this population over 2 consecutive years. Complete meiotic drive in favour of the M4-d chromosomes in heterozygous females would explain the maintenance of its frequency despite the fact that it is counterselected.