This study examines (a) the knowledge that secondary school students have concerning some basic aspects related to the location of inheritance information before they are taught about genetics (b) the effects of traditional instruction (in Spain) on students learning about these subjects (c) the characteristics of the teaching programs that are implemented in Spain (d) the characteristics of a teaching program on the location of inheritance information based on constructivism and (e) the learning achieved as a consequence of the implementation of this program (compared with what is learned by pupils who study genetics in a more traditional way)