Immunological method for mapping genes on Drosophila polytene chromosomes.

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Abstract
A method is described for localizing DNA sequences hybridized in situ to Drosophila polytene chromosomes. This procedure utilizes a biotin-labeled analog of TTP that can be incorporated enzymatically into DNA probes by nick-translation. After hybridization in situ, the biotin molecules in the probe serve as antigens which bind affinity-purified rabbit antibiotin antibodies. The site of hybridization is then detected either fluorimetrically, by using fluorescein-labled goat anti-rabbit IgG, or cytochemically, by using an anti-rabit IgG antibody conjugated to horseradish peroxidase. When combined with Giemsa staining, the immunoperoxidase detection method provides a permanent record that is suitable for detailed cytogenetic analysis. This immunological approach offers 4 advantages over conventional autoradiographic procedures for detecting in situ hybrids: the time required to determine the site of hybridization is decreased markedly; biotin-labeled probes are chemically stable and give reproducible results for many months; biotin-labeled probes appear to produce less background noise than do radiolabeled probes; and the resolving power is equal to and often greater than that achieved autoradiographically.