Figure 2

Chromosomal location of 5S rDNA, major rDNA and core histone genes on Brachidontes puniceus and Brachidontes rodriguezi. FISH using a 5S rDNA probe (digoxigenin, rhodamine, red) reveals the presence of two clusters of 5S rDNA on two chromosome pairs in both B. puniceus (BPU, a) and B. rodriguezi (BRO, b). Double-FISH experiments using a 5S rDNA probe (digoxigenin, rhodamine, red) and a 28S rDNA probe (biotin, fluorescein, green) show that major and minor gene clusters in B. puniceus (c) are to be found on different chromosome pairs but that in B. rodriguezi (d) one of the chromosome pairs bearing a 5S rDNA signal also bears one of the major rDNA signals. FISH using a histone H3 gene probe (biotin, fluorescein, green) shows two clusters of core histone genes on the long arms of two chromosome pairs in both B. puniceus (e) and B. rodriguezi (f). Triple hybridization (g, h) using a digoxigenin labeled 5S rDNA probe (red), a biotin labeled histone H3 gene probe (red) and a double (biotin and digoxigenin) labeled 28S rDNA probe (yellow, as a result of the mixture of green and red) reveals that the histone gene clusters are independent of the major rDNA clusters in B. puniceus (g, i) and in B. rodriguezi (h, j).

In both species, one of the chromosome pairs bearing a 5S rDNA signal also carries one of the core histone gene signals (g, h, i, j). The metaphase plate in g, i was also re-hybridized using a PNA telomeric probe (fluorescein, green). Scale bars, 5 μm.