A comparison of intron 1 CA-rich sequences. Intron 1 sequences that encompass the CA-rich regions from the 11 inbred strains are aligned for comparison. Two haplotypes can be distinguished: Haplotype 1 (represented by the top 7 sequences) contains a contiguous stretch of 21 CA repeats (nucleotides 250-291, based on the BALB/cJ sequence, setting the A of the ATG start codon to 1). Haplotype 2 (represented by the bottom 4 sequences) contains no more than 6 consecutive CA repeats within the same region. The sequence within haplotype 1 is designated CA21; that within haplotype 2, CA6.