Chapter 15 The Chromosomal Basis of Inheritance Lecture Outline Overview: Locating Genes on Chromosomes Genes are located on chromosomes. Concept 15.1 Mendelian inheritance has its physical basis in the behavior of chromosomes Around 1900, cytologists and geneticists began to see parallels between the behavior of chromosomes and the behavior of Mendel?s factors. Using improved microscopy techniques, cytologists worked out the process of mitosis in 1875 and meiosis in the 1890s. Chromosomes and genes are both present in pairs in diploid cells. Homologous chromosomes separate and alleles segregate during meiosis. Fertilization restores the paired condition for both chromosomes and genes.