def Double_list (list_genomes):
    """
    Create the new headers of the contig/s of the individual genomes and save the
    headers and sequences in different lists. In the same position in a list 
    it will be the header and in the other its respective nucleotide sequence.
    """
    # Create the lists:
    headers = []
    seqs = []
    # In each genome, modify the headers and then save the headers and sequences
    # in diferent lists.
    for file in list_genomes:
        n = 0
        # Open the file to read.
        file_in = open(file, 'r')
        for line in file_in:
            line = line.strip()
            if line[0] == '>':
                n += 1
                # New format of header.
                header = '>' + file[:-6] + '_' + str(n)
                headers.append(header)  
            else:
                seqs.append(line)
    
    return headers, seqs