A variety of animals use Earth's magnetic field as a reference for their orientation behaviour. Although distinctive magnetoreception mechanisms have been postulated for many migrating or homing animals, the molecular mechanisms are still undefined. In this study, we found that zebrafish, a model organism suitable for genetic manipulation, responded to a magnetic field as weak as the geomagnetic field. Without any training, zebrafish were individually released into a circular arena that was placed in an artificial geomagnetic field, and their preferred magnetic directions were recorded. Individuals from five out of the seven zebrafish groups studied, groups mostly comprised of the offspring of predetermined pairs, showed bidirectional orientation with group-specific preferences regardless of close kinships. The preferred directions did not seem to depend on gender, age or surrounding environmental factors, implying that directional preference was genetically defined. The present findings may facilitate future study on the molecular mechanisms underlying magnetoreception.
In the previous models, it was assumed that there is no change in the genetic properties from parents to offspring. The present study was undertaken with the purpose of developing a more practical prediction model of long-term selection response taking into account the genetic change caused by segregation and recoupling of gametes. Under the assumption of equal gene effects, we can obtain the distribution of genetic value of gametes using hypergeometric distribution.Then the change of genetic properties with long-term selection can be predicted by the repeated use of the procedures of selection on phenotype, segregation into gametes and recoupling of gametes. In comparison with the previous models without genetic change from parents to offspring, the following results are shown; 1) the variance of breeding value declines more slowly because of the variance caused by segregation and recoupling of gametes, 2) the mean increases more rapidly because of larger genetic variance and 3) the skewness changes more slowly especially in earlier generations.Jpn. J. Zootech. Sci., 59 (6): 554-559, 1988 Key words: prediction model, long-term selection, selection responseThe selection response per generation cannot be held constant, because selection changes the genetic properties of population from genertion to generation. The prediction of genetic change under a long-term selection pressure is fundamentally important to control the genetic properties of population.In the previous models1-5) to predict long-term selection response, it was assumed that there is no difference in genetic properties between parents and offspring in order to simplify the subject. The genetic properties are, however, changed by the segregation and recoupling of gametes under the pressure of selection.In order to obtain a higher accuracy of prediction, we studied the effects of segregation and recoupling of gametes under a gene-assumed model.
Basis and proceduresThe genetic change with generations contains segregation and recoupling of gametes. Therefore, we have to obtain the distribution of gamete generated from Jpn. J. Zootech. Sci., 59 (6): 554-559 554 1988
The authors proposed the method for selecting fixed effects in sire evaluation models using Akaike By calculating ABIC's for 15 alternative models, the model which included the combined fixed effect of {Calf born year}-{Slaughter house}-{Age class at slaughter} was selected as the best fit model for the five traits except Carcass price per weight, and the model which included the combined fixed effect of {Calf born year}-{Fatted prefecture}-{Age class at slaughter} was selected for Carcass price per weight.Slaughter house and Fatted prefecture were not included in one model at the same time, because these effects were strongly confounded.Sire born prefecture and Calf born prefecture were not employed in the best fit models.These results suggested that combined fixed effects were useful effects of the model in the Japanese Black sire evaluation.In the future, Fatting method which is not confounded with Slaughter house should be considered in stead of Fatted prefecture.
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