def strip_chr(chr):
    """Removes the 'chr' prefix if present.

    Args:
        chr (str): The chromosome.
        
    Returns:    
        str: The chromosome without a 'chr' prefix.
        
    Examples:
        >>> strip_chr('22')
        '22'

        >>> strip_chr('chr22')
        '22'
    """
    return chr[3:] if chr[0:3] == 'chr' else chr