POLYMORPHIC SEQUENCE IN THE D-LOOP REGION OF EQUINE MITOCHONDRIAL-DNA

The D-loop regions in equine mitochondrial DNA were cloned from three thoroughbred horses by polymerase chain reaction (PCR). The total numb er of bases in the D-loop region were 1114 bp, 1115 bp and 1146 bp. Th e equine D-loop region is A/T rich like many other mammalian D-loops. The large central conserved sequence block and small conserved sequenc e blocks 1, 2 and 3, that are common-to other mammals, were observed. Between conserved sequence blocks land 2 there were tandem repeats of an 8 bp equine-specific sequence TGTGCACC, and the number of tandem re peats differed among individual horses. The base composition in the un it of these repeats is G/C rich as are the short repeats in the D-loop s of rabbit and pig. Comparing DNA sequences between horse and other m ammals, the difference in the D-loop region length is mostly due to th e difference in the number of DNA sequences at both extremities. The s imilarities of the DNA sequences are in the middle part of the D-loop. In comparison of the sequences among three thoroughbred horses, it wa s determined that the region between tRNA(Pro) and the large central c onserved sequence block was the richest in variation. PCR primers in t he D-loop region were designed and the expected maternal inheritance w as confirmed by PCR-RFLP (restriction fragment length polymorphism).