Interestingly, FISH with the labeled fragment of 18S rDNA stained the whole short arm of the latter mentioned submetacentric chromosome (Figure 1b). FISH signals of the labeled 18S rDNA on these chromosomes were very strong and made it difficult to observe signals in other chromosomal regions (Figure 1b). Nevertheless, an additional small FISH signal could be observed near the termini of some other chromosomes. For detailed analysis, the level of the weak signal was artificially increased (Figure 1c). In this way, small clusters of 18S rDNA were detected in numerous sites. They varied in size and were colocalized or localized near to the clusters of telomeric repeats. Additionally, interstitial clusters of telomeric repeats (Interstitial Telomeric Sequences—ITSs) were present in many chromosomes. Usually they were located not far from clusters of telomeric repeats in the termini of long arms. In some chromosomes, they were close to the clusters of telomeric repeats in the termini of long arms and were almost fused with them (Figure 1b,c). In the future, the pattern of the here applied probes together with other repetitive DNA probes might be used to clearly identify individual chromosome pairs. An attempt to do this based on C-banded chromosomes is shown in Figure 2a.