New mutations are a very relevant component of polygenic variability and they must be viewed as the raw material for the maintenance of genetic diversity. Nevertheless, the biological phenomena that originate new mutational variants are poorly understood, particularly in regard to the effects that factors such as a parent’s age may have. This research focuses on the analysis of weaning weight (10.48 ± 0.02 g) in 12,644 C57BL/6J mice from 46 non-overlapping generations. Data (y) were analyzed under the following model: y = Xb + Z₁p + Z₂a + Z₂m_p + Z₂m_m + e, where systematic (b), permanent environmental (p), and additive genetic effects (a, m_p and m_m) were linked by appropriate incidence matrices (X, Z₁ ande Z₂). Note that mutational effects where modeled depending on their origin (i.e., paternal, m_p; maternal, m_m), and an independent set of parent-specific mutational effects were estimated on the basis of new mutations arising to each individual in the pedigree file (i.e., m_p = m_p,1 + m_p,2 + … + m_p,12644). Within this context, m_p,i was assumed multivariate normal (MVN) distributed, p(m_p,i|M_i,σ_mp²,λ_p) = MVN(0,0.5M_iσ_mp² [1+ε_p,iλ_p])M_i being the matrix of mutational relationships specific to new mutations arising in the ith individual, σ_mp² (σ_mm²) being the paternal (maternal) mutational variance, ε_p,i being sire's age when conceiving ith individual, and λ_p being a linear regression coefficient linking mutational variance and sire's age. This model was solved under a standard Bayesian approach. Mode (and credibility interval) for σ_mp² and σ_mm² were 0.113 (0.069 to 0.163) and 0.052 (0.020 to 0.097), respectively. Whereas linear regression coefficient for dam's age collapsed to 0 and discarded additional changes in σ_mm², λ_p reached a modal estimate of 0.001 (10⁻⁵ to 0.051); e.g., this linearly increased σ_mp² from ~0.11 g² (puberal sires) to 0.154 g² (one-yr-old sires). This parameterization allowed us to clearly characterize different mutational patterns associated with the sex of the parent, as well as the effect of the accumulation of new mutations along breeding stock’s lifetime.