This lecture explores how the transmission of genetic traits is affected when two genes are located on the same chromosome. Through the study of Drosophila genetics, the instructor demonstrates genetic linkage and recombination, showing how the physical proximity of genes influences their inheritance patterns. The lecture covers the concept of genetic maps, illustrating how the frequency of recombination between genes can be used to map their positions on a chromosome. Additionally, the impact of environmental factors on phenotype expression is discussed, highlighting how gene interactions and environmental conditions can shape observable traits. The presentation concludes with a summary emphasizing the importance of understanding genetic linkage and recombination in studying inheritance patterns.