Recurrent patterns of chromosome variation in a species group

Abstract

The chromosome characteristics of five closely-related species in Rumex subgenus Acetosa are considered. All are dioecious diploids with 2n = 12 + XX in females and 2n = 12 + XY1Y2 in males. The autosomes of all species are very similar, all highly acrocentric and displaying apparent homoeology, and only two chromosome changes have occurred in the evolution of the group -shift of an NOR and deletion of part of the long arm of chromosome 6. The heterochromatic Y-chromosomes are more variable and only two species cannot be identified by examination of the Ys alone. Hypervariability in centromere location is characteristic of Ys in the whole subgenus although there is no quantitative variation in heterochromatin. On the autosomes, parallel polymorphisms for heterochromatic supernumerary segments on the short arms of pairs 1, 5 and 6 are found in 4 of the 5 species, and euchromatic B-chromosomes are common in three species. These recurrent patterns of chromosome variation emphasise the close relationships within the species group. © 1988, The Genetical Society of Great Britain.