def get_genes_in_range(pos_hash, start, end):
    """Returns list of genes that occur in a given range of coordinates.

    Arguments:
        pos_hash (dict): Dictionary of position to list of genes.
        start (int): Start coordinate of the desired range.
        end (int): End coordinate of the desired range.

    Returns:
        list: List of genes that fall within range.

    """
    genes = set()
    for pos in range(start, end + 1):
        if pos in pos_hash:
            genes.update(pos_hash[pos])
    return list(sorted(genes))
