Complete mitochondrial genomes of Bos taurus and Bos indicus provide new insights into intra-species variation, taxonomy and domestication.

The taurine and zebuine cattle breeds comprise the majority of the world cattle population but their taxonomic status is still controversial. The two forms of cattle are currently classified as Bos taurus and Bos indicus species and are differentiated primarily by the presence or absence of a hump. However, these two species hybridize readily, producing fully fertile offspring. We have determined and analyzed complete B. taurus and B. indicus mitochondrial genome sequences to investigate the extent of sequence divergences and to study their taxonomic status by molecular dating. The sequences encompassed 16,338 and 16,339 nucleotides, respectively, and differed at 237 positions. Estimated divergence times indicated that the two cattle lineages separated 1.7-2.0 million years ago. Combined phylogenetic analyses of 18 new and 130 previously reported extant B. taurus and B. indicus control region sequences with data from 32 archaeological specimens of the extinct wild aurochs (Bos primigenius) identified four major maternal lineages. B. primigenius haplotypes were present in all but the B. indicus lineage, and one B. taurus sequence clustered with B. primigenius P haplotypes that were not previously linked with domestic cattle. The B. indicus cluster and a recently reported new B. primigenius haplotype that represents a new lineage were approximately equidistant from the B. taurus cluster. These data suggest domestications from several differentiated populations of B. primigenius and a subspecies status for taurine (B. primigenius taurus) and zebuine (B. primigenius indicus) cattle.

The complete mitochondrial DNA sequence of the domestic sheep (Ovis aries) and comparison with the other major ovine haplotype.

The complete mitochondrial DNA (mtDNA) molecule of the domestic sheep, Ovis aries, was sequenced, together with part of the mtDNA of a specimen representing the other major O. aries haplotype group. The length of the complete ovine mtDNA presented is 16,616 nucleotides (nt). This length is not absolute, however, due to heteroplasmy caused by the occurrence of different numbers of a 75-nt-long tandem repeat in the control region. The sequence data were included in analyses of intraspecific ovine molecular differences, molecular comparisons with bovine mtDNAs, and phylogenetic analyses based on complete mtDNAs. The comparisons with bovine mtDNAs were based on the central domains of the ovine control regions, representing both major ovine haplotype groups, and the corresponding domains of Bos taurus and B. indicus. The comparisons showed that the difference between the bovids was 1.4 times greater than the intraspecific ovine difference. These findings suggest that the strains of wild sheep from which domestic sheep originated were more closely related than were the B. primigenius subspecies which gave rise to B. indicus and B. taurus cattle. Datings based on complete mtDNAs suggest that the bovine and ovine lineages diverged about 30 million years before present. This dating is considerably earlier than that proposed previously.

Analysis of mitochondrial DNA indicates that domestic sheep are derived from two different ancestral maternal sources: no evidence for contributions from urial and argali sheep.

To investigate the origins and phylogenetic relationships of domestic sheep, mitochondrial DNA (mtDNA) from 243 sheep of five European, one African, and four Asian breeds and several mouflon (Ovis musimon), urial (O. vignei bochariensis), and argali (O. ammon nigrimontana, O. a. collium) were assayed for restriction fragment length polymorphisms (RFLP). Twenty haplotypes were identified which occurred in three major phlogenetic groups: urial/argali, mouflon/domestic, and domestic sheep. From the branches that contain mouflon and domestic sheep, two major domestic sheep lineages are apparent. One lineage, termed European lineage, contains the majority of haplotypes detected among European domestic sheep. These mtDNAs resemble mouflon haplotypes. The other lineage, termed Asian lineage, consists of haplotypes found in central Asian and some European domestic sheep. The mean sequence difference between these two lineages (0.72%) is of similar magnitude as that between two argali subspecies. To accurately estimate sequence differences between the European and Asian mtDNA types, the mitochondrial control region of one animal from each lineage and of one mouflon and urial were completely sequenced. Sequence comparisons show that Asian and European domestic sheep lineages differ by 4.43%. The mouflon sequences diverges from the Asian type by 4.52%, but by only 1.36% from the European type. Our data supports the hypothesis that some modern domestic sheep and European mouflon derive from a common ancestor and provide evidence of an additional wild ancestor, other than the urial and argali groups, which has yet to be identified.

Flow cytometric detection of unbalanced ram spermatozoa from heterozygous 1;20 translocation carriers.

Flow cytometric analysis of enzymatically decondensed, DAPI-stained spermatozoa was performed to confirm the suspected production of unbalanced spermatozoa in heterozygous rams carrying a 1;20 translocation. High-precision flow cytometry (coefficient of variation, 0.6-0.8%) with a PAS II flow cytometer depicted Y- and X-chromosome-bearing spermatozoa from three cytogenetically normal rams as two distinct peaks. The difference in DNA fluorescence intensity between the gonosomes averaged 4.8%. Analysis of sperm samples from three heterozygous 1;20 translocation carriers yielded histograms with five peak distributions. The individual peaks were attributed to spermatozoa with a normal, balanced, and unbalanced chromosomal status. Peaks within Y- and X-spermatozoa populations were distributed in a ratio of 1:2:1 and were almost completely separated, with a coefficient of variation of 0.5-0.6%. Owing to the relative size of the translocated chromosomal segment (2.4% of the total DNA content, as determined from the flow cytometric data), histograms with five instead of the expected six peaks were observed.