Abstract

The chromosomes of the Chilean frog Eupsophus insularis are described for the first time. This species has a chromosome number of 2n = 30, and based on the karyotype it is concluded that E. insularis is closely related to E. migueli. E. insularis has an XX/XY system of sex determination, and pericentromeric constitutive heterochromatin is present in all chromosomes except in the Y chromosome. It is postulated that the Y chromosome is derived from a small ancestral metacentric chromosome that lost its heterochromatic segment.