The primary unit of heredity in living organisms is the gene. Genes are segments of DNA that encode the instructions for producing proteins responsible for various traits and functions within an organism. They are inherited from parents and can vary in expression based on environmental factors, leading to phenotypic diversity. Understanding gene transmission and expression is vital for studies in genetics, evolution, and biotechnology. Research in genetics helps uncover the underlying mechanisms of heredity, paving the way for advancements in medicine, agriculture, and conservation.