Cytoplasmic and mitochondrial inheritance of economic traits in cattle

Bovine mitochondria contain a 16338 nucleotide closed loop of DNA coding for 13 translated genes, 22 tRNA and 2 rRNA and is inherited exclusively through the maternal line, providing a genetic mechanism for cytoplasmic inheritance. Several early analyses of cattle populations indicating significant cytoplasmic variance in production traits were criticized on statistical grounds, Analysis under an animal model has revealed significant effects on milk fat concentration in two studies with Holsteins, but not in two other studies and no significant effects were found for growth and lactation traits in two beef cattle studies. Studies relating dairy performance to mitochondrial nucleotide variation across previously analyzed mitochondrial lineages found significant associations, but do not provide an independent test of mitochondrial effects. In a separate population no associations were found. The evidence is broadly consistent with 0 to 5% of variation in performance due to cytoplasmic effects, with the weight of evidence pointing to the low end of this range. If at the upper end of this range, however, cytoplasmic effects could be of practical importance. (C) 1997 Elsevier Science B.V.