My goal is to present the analysis of concepts on the “normal” karyotype and chromosomal abnormalities through comprehension of chromosomal variation within fruit flies populations, advantages of these insects as models to study genetic polymorphisms and the methodology from field to strains. Cytological preparations were obtained from cerebral ganglion. Staining methods include routine and fluorescent bandings as well as in situ hybridization using DNA probes. We define a more frequent karyotype of each one species and take them as the reference karyotype. The reference as well as the chromosomal variants studied within each species were isolated in different strains. The techniques applied revealed differences among individuals belonging to different strains, thus documenting the mutations into the DNAr cluster, variation in the patterns of heterochromatin, mosaic specimens carrying nuclei with different chromosomal numbers. Hoecht revealed double‐minute chromosomes and CG‐ rich banding marked somatic crossing over between sister chromatids. The most frequent karyotype is the reference karyotype, namely, the normal karyotype. Chromosomal mutations produce variability. In man, a number of these mutants are considered chromosomal abnormalities. We learnt that variation is the key to survival and that many individuals could be in the right place in the wrong moment.
Part of the book: Chromosomal Abnormalities