Diagram of factor VIII intron 1 and proposed model for inversion.

(A) Bar shows factor VIII intron 1, flanked by exons (drawn to indicate the direction of transcription), and containing a repeated sequence 9b (shaded) flanked by unique sequences 9a and 9c. The line shows DNA outside the F8 gene with the repeated sequence as a shaded box. Arrowheads indicate orientation of repeated sequences. The large curved arrow indicates the folding required for homologous recombination. (B,C) Homologous recombination between the two 9b repeats proposed to explain origin of inversion. (D) Inversion resulting from recombination. This shows why in the DNA of UKA29 PCR amplification succeeds for fragments 9ab and 9bc but not for 9ac. CEN indicates centromeric; TEL, telomeric.