FISH with Whole Chromosome Painting Probes

Some types of chromosome aberrations are not easily identified by the traditional Giemsa staining. It usually needs some banding technique and skilled person's eye. Whole chromosome painting FISH probe can stain designated entire chromosomes or domains in metaphase chromosomes or interphase nuclei, respectively. It allows to visually identify translocations, deletions, or amplifications of specific chromosomes. Once chromosomes are stained, even non-skilled researchers can easily identify those chromosome aberrations. Whole chromosome painting FISH has higher sensitivity to detect chromosome aberrations. This chapter introduces the method for whole chromosome painting FISH staining.

Reciprocal Translocation Analysis with Whole Chromosome Painting for FISH

Ionizing radiation can produce many chromosome aberrations; however, a number of aberrations are not readily detectable with a conventional Giemsa staining and require special staining methods. Moreover, an easy method to identify nondetectable chromosomal aberrations, such as symmetrical inter-chromosomal translocations, is available: whole chromosome fluorescence in situ hybridization (FISH) staining. Asymmetrical translocations such as dicentric chromosomes are known to be lethal but cells with symmetrical translocations may survive and persist in the progeny population for years. Chromosome banding techniques can also detect inter-chromosomal translocations but understanding banding patterns requires professional training and experience. Due to its clear detection by a discernible painting color, whole chromosome painting method is superior in identifying chromosome fragmentation, loss, and amplification of chromosomes. This chapter introduces whole chromosome FISH painting method to detect chromosomal aberrations such asfragments and translocations.

Early Stages of XY Sex Chromosomes Differentiation in the Fish Hoplias malabaricus (Characiformes, Erythrinidae) Revealed by DNA Repeats Accumulation

BACKGROUND

Species with 'young' or nascent sex chromosomes provide unique opportunities to understand early evolutionary mechanisms (e.g. accumulation of repetitive sequences, cessation of recombination and gene loss) that drive the evolution of sex chromosomes. Among vertebrates, fishes exhibit highly diverse and a wide spectrum of sex-determining mechanisms and sex chromosomes, ranging from cryptic to highly differentiated ones, as well as, from simple to multiple sex chromosome systems. Such variability in sex chromosome morphology and composition not only exists within closely related taxa, but often within races/populations of the same species. Inside this context, the wolf fish Hoplias malabaricus offers opportunity to investigate the evolution of morphologically variable sex chromosomes within a species complex, as homomorphic to highly differentiated sex chromosome systems occur among its different karyomorphs.

MATERIALS & METHODS

To discover various evolutionary stages of sex chromosomes and to compare their sequence composition among the wolf fish´s karyomorphs, we applied multipronged molecular cytogenetic approaches, including C-banding, repetitive DNAs mapping, Comparative Genomic Hybridization (CGH) and Whole Chromosomal Painting (WCP). Our study was able to characterize a cryptically differentiated XX/XY sex chromosome system in the karyomorph F of this species.

CONCLUSION

The Y chromosome was clearly identified by an interstitial heterochromatic block on the short arms, primarily composed of microsatellite motifs and retrotransposons. Additionally, CGH also identified a male specific chromosome region in the same chromosomal location, implying that the accumulation of these repeats may have initiated the Y chromosome differentiation, as well as played a critical role towards the evolution and differentiation of sex chromosomes in various karyomorphs of this species.