Joint scaling tests

Genetic basis of voluntary water consumption in two divergently selected strains of inbred mice

Background

Inbred mouse strains with normal renal function show a substantial difference in daily water consumption across strains. This study uses two strains of inbred mice C57BR/CDJ (BR), which are high consumers, and C57BL/10J (BL), which are low consumers, their reciprocal F₁ crosses, inter se bred F₂s and backcrosses produced by breeding high consuming F₂ animals to the low consumer parent strain and low consuming F₂ animals to the high consuming parent strain. Consumption was corrected for body weight prior to analysis.

Methods

The effective number of genes controlling water consumption was estimated using the Castle–Wright estimator. Additive and dominance genotypic values as well as the degree of dominance were calculated using estimated strain means.

Results

According to Castle–Wright, a minimum of 10 factors were estimated to affect the difference in consumption across the two strains. Between seven and eight are expected to be high effect factors. Using the Zeng adjustment, it was determined that 30–40 factors potentially affect the difference in consumption.

Conclusions

These numbers were surprising but may be related to several sources of variation present in the BR strain. A negative degree of dominance indicated the BL strain has more dominant factors.

The genetic architecture of behavioural responses to novelty in mice

The genetic architectures of 12 behavioural variables measured in adult male mice placed in a novel environment were analysed in a replicated 4 X 4 diallel cross. The results were combined with those obtained in a classical cross involving two of the four strains. Based on the hypothesis of an evolutionary history of stabilising selection for mouse exploratory behaviour, we expected additive genetic effects and ambidirectional dominance. Such genetic architectures were actually found for those exploratory behaviours where epistatic effects were of minor importance. Similar findings emerged for some non-exploratory phenotypes. All behaviours analysed appeared to be polygenically controlled.