Molecular cytogenetics involves the combination of molecular biology and cytogenetics. In general this involves the use of a series of techniques referred to as fluorescence in situ hybridization, or FISH, in which DNA probes are labeled with different colored fluorescent tags to visualize one or more specific regions of the genome. FISH can either be performed as a direct approach to metaphase chromosomes or interphase nuclei. Alternatively, an indirect approach can be taken in which the entire genome can be assessed for copy number changes using virtual karyotyping. Virtual karyotypes are generated from arrays made of thousands to millions of probes, and computational tools are used to recreate the genome in silico.
Studies of meiosis
In eukaryotes, the Rad51 and Dmc1 proteins have a central role in meiosis. Teresawa et al. using immunofluorescence microscopy found that in Lilium longiflorum, Rad51 and Lim15 (an ortholog of Dmc1) co-localize on meiotic prophase I chromosomes where they form discrete foci. Using electron microscopic immunogold labeling localization, Anderson et al. found Rad51 and/or Lim15 proteins to be components of early meiotic nodules that are involved in recombination related events. The stages of meiosis in which the co-localization of the Rad51 and Lim15 proteins occurs are the leptotene and zygotene stages of meiosis, suggesting that meiotic recombination begins at the leptotene stage with the cooperation of these proteins and continues into zygotene. These proteins catalyze pairing of homologous chromosomes, DNA strand exchange, and recombinational repair of DNA damages.