This study was conducted to establish prior perceptions and ideas held by students on the topics of Genetics and Evolution. The students, as used here refers to learners in the Boys', the Girls', Mixed secondary schools and the Genders as independent variables, while the perceptions and ideas characterized the dependent variables. The study was guided by Bruner's constructivist theory. Methodology was a stratified random sampling of the secondary schools. Data collection used two Questionnaires: Students' Questionnaire and Teachers' Questionnaire. The respondents were 269 students selected randomly from 9470 form three students and 18 Biology Teachers of 77 Teachers of Biology in Kakamega district, Kenya. The data analyzed using frequencies, percentages and chi-square test. The study established that the students found the concepts and sub-concepts difficult or the teachers had not used best strategies to teach them evidenced from the vague and incoherence of wrong versions. Social-cultural and religious teachings were the sources of the wrong versions and misconceptions by students. The teachers found teaching of Genetics and Evolution challenging as was evidenced by poor coverage