For low abundant cDNA or non-expressed genes, you may have to screen genomic library with labeled cDNA that you already have as probes. Separate the clones based on the intensity of the hybridization signal with probes of different regions of the cDNA (5'-probe, mid-region, and 3'-probe). Identical clones will give strong signal, and distant homologs will give weaker signal. Characterize the clones by restriction digestion and DNA sequencing.
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