sentences:  The most significant effect concerns achondroplasia (a form of dwarfism), which might occur in about 1 in 1,875 children fathered by men over 50, compared to 1 in 15,000 in the general population.However, the risk for achondroplasia is still considered clinically negligible.The "FGFR" genes may be particularly prone to a paternal age effect due to selfish spermatogonial selection, whereby the influence of spermatogonial mutations in older men is enhanced because cells with certain mutations have a selective advantage over other cells (see § DNA mutations).