def remove_extra_loci(patterns):
    """
        If a pattern has more than one possible loci, return only one
        Input:
            patterns: A dictionary of patterns
        Output: A dictionary of patterns with only a single loci per pattern.
    """
    return {pattern: {list(loci.keys())[0]: loci[list(loci.keys())[0]]}
            for pattern, loci in patterns.items()}