It has been known that genetic predisposition is involved in intramuscular fat accumulation in beef cattle. However, causative gene (s) for intramuscular fat accumulation still remain (s) unidentified. In order to detect the gene (s) responsible for intramuscular fat accumulation which is thought as a quantitative trait, the application of inbred rat models is an essential component due to usefulness of them in quantitative trait loci (QTL) analysis, congenic analysis, and positional candidate cloning approach. It is, therefore, important to detect rat model for intramuscular fat accumulation. Our investigation was designed to detect inbred rat strains, in which intramuscular fat content is preferentially markedly increased as compared to intra-abdominal and subcutaneous fat contents, by measuring intramuscular, intra-abdominal, and subcutaneous fat contents in males and females of 10 obese inbred strains at 25 weeks of age. These strains exhibited higher levels of intramuscular fat content than normal control rat, and fatty (fa) mutation affected an increase of intramuscular fat content. OLETF strain possessed sex difference in degree of intramuscular fat accumulation. Three strains, Zucker fatty, LEA, and SHC, but not other strains, irrespective of sex, exhibited preference of accumulation of intramuscular fat to of intra-abdominal and subcutaneous fats. Thus, these three strains seem to be useful as rat model for genetic analysis of intramuscular fat accumulation. In addition, we observed the correlation between plasma triglyceride levels and body fat contents, suggesting an important role of the plasma triglyceride level as a concise diagnostic indicator for prediction of body fat contents.
For populations in linkage equilibrium, the accuracy of marker-assisted combined selection (MACS) for quantitative characters relative to the conventional scheme of combined selection based on trait phenotype information only is investigated using a deterministic approach. It is assumed here that trait records can be obtained in both sexes. For MACS, two cases in which information about a single marker and two flanking markers linked to one quantitative trait locus (QTL) is available are considered, allowing the occurrence of recombination. The difference in the relative accuracy between the two cases of MACS is shown to be totally small. The influences of sizes of full- and half-sib families on the relative accuracy of MACS are likely to be small, relative to those of the magnitudes of heritability and the proportion of additive genetic variance due to the QTL. The influences of the length of, and the position of the QTL within, the interval bracketed with two markers are found to be also small. It is revealed that the accuracy of MACS is very close to that of the combined selection under the situation with the QTL allele transmission known exactly. For the trait as considered here, it is indicated that a slight gain in the accuracy is attained in MACS of the current type compared to the conventional scheme.
To elucidate the evolution of vertebrate genomes, it is important to estimate the number of protein-coding genes in the genome. The numbers of protein-coding genes of mouse genome were estimated by clustering full length mRNA sequences from DDBJ/EMBL/GenBank and sequencing data of the expressed sequence tags using by genome informatics procedure. The estimates of the total number of protein-coding genes were 33, 924.