FISH of 5S rDNA and telomeric (TTAGGG) n repeats in normal and translocated populations of the frog Quasipaa boulengeri (Anura, Ranidae)

Abstract

Quasipaa boulengeri, a spiny frog, is widely distributed in the low mountain regions, around Sichuan Basin. Our previous study revealed five karyotypes, caused by a translocation, that are randomly distributed throughout different populations. 5S rDNA and telomere sequence (TTAGGG)n are potential good markers for chromosome identification and karyological evolution. In this study, we examined the sequences of 14 populations using fluorescence in situ hybridization (FISH) to detect if there is any variation between karyologically normal and translocated populations. 5S rDNA loci were located at the same position on chromosomes 1 in 7 translocated populations. In two of the seven normal populations, 5S rDNA also occurred on chromosome 5 in addition to chromosome 1. Our findings further indicate that the 5S rDNA on No. 1 most likely represents the ancestral condition, while the minor loci represent the derived state. Signal density variations of the 5S rDNA were observed beteween homologous chromosomes or sister chromatids of pair 1 in both normal and translocated populations. Telomere sequences were identically located on all ends of the 26 chromosomes in seven rearranged populations, however, no ITSs were observed on the translocated chromosomes 1 and 6. Two of the six normal populations were found to contain ITSs which indicates that populations with translocation events diverged prior to those with ITSs rearrangements. In the KKS and BF populations, the ITSs of chromosome 3 are not always found on both homologues. Inter-chromosomal signal strength of telomeric sequences commonly differs within all populations.