A classical Mendelian cross-breeding study of the Naples high and low excitability rat lines

The heritability of HVA trait was estimated across the 20 generations of selection and Mendelian cross hybrids. Quantitative-genetic analysis on this trait and its HA and VA components, was applied by the Lynch and Walsh joint-scaling test procedure to evaluate underlying genetic mechanism. The correlation between experimental data of hybrids and estimated values from different heritability models were also computed. Results indicated that (i) the activity scores by Mendelian hybrids were intermediate between the two parental lines and were also graded; (ii) there was no sex effect on the heritability of trait but only a general tendency of females to higher activity levels; (iii) the heritability of HVA trait was very high (h2 index = 0.824); (iv) heritability model of HVA and HA trait was polygenic with a marked epistatic control where as VA trait was fitted by simpler model with less genes and lower epistatic effect. In conclusion the Naples lines reveal strong genetic determinants for behavioural traits associated with polygenic pattern. Moreover, HA and VA activity components with prevailing cognitive and non-cognitive meaning, respectively, show differential genetic control.