Sequence heteroplasmy of D-loop and rRNA coding regions in mitochondrial DNA from Holstein cows of independent maternal lineages

A mitochondrial DNA (mtDNA) fragment containing the D-loop, phenylalanine t RNA, valine tRNA, and 12S and 16 rRNA genes was cloned and sequenced from 3 6 cows Of 18 maternal lineages to identify the polymorphic sites,within tho se regions and to detect the existence of heteroplasmic mtDNA in cows. Seve nteen variable sites were observed within the D-loop and rRNA coding region s of bovine mtDNA within a 2.5-kb span. The hypervariable sites ill the D-l oop and rRNA coding regions were identified at nucleotide positions 169, 21 6, and 1594. Heteroplasmic mtDNA (variable mtDNA within a tissue) existed e xtensively in cows and was detected within the above regions in II of 36 co ws sequenced The insertion, deletion, and nucleotide transversion polymorph isms Mere found only in homopolymer regions. Heteroplasmy was observed freq uently and seemingly is persistent in cattle. Though heteroplasmy was demon strated, most lineages and mtDNA sites showed no heteroplasmy.