In Situ Localization of Parental Genomes in a Wide Hybrid

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Abstract
In situ hybridization enabled DNA originating from the two parental genomes to be distinguished in plant hybrids. A probe of biotinylated total genomic DNA from Secale africanum labelled the chromosomes of S. africanum origin but not those from Hordeum chilense in root-tip chromosome spreads of the sexual hybrid between the two species. Hybridization of total genomic DNA from S. africanum to DNA on filters (dot blots) confirmed the distinction between DNA from Hordeum and Secale. The total genomic probe hybridized to the whole length of the chromosomes from S. africanum remarkably uniformly, labelling both euchromatin and heterochromatin, except at the centromeric region. The probe binding was visualized as a yellow colour by the fluorescein-coupled detection system which contrasted with the red fluorescing counterstain of the unlabelled chromatin. The chromosomes originating from both parents could be seen and distinguished as red and yellow fluorescence at all stages of the cell cycle. At interphase and prophase, the chromatin originating from the two parental genomes did not mix. Chromosomes or groups of chromosomes occupied distinct domains and also tended to be arranged in a Rabl configuration with the centromeres clustered at one end of the nucleus. We propose calling the technique using total genomic DNA as a probe ‘genomic in situ hybridization.’