1: History of genetics

Section 1: Fundamentals - History of Genetics

Understanding genetics requires tracing its roots, moving beyond the simple observation of inherited traits to the discovery of fundamental mechanisms. Early ideas were often speculative. Ancient Greek philosophers like Hippocrates proposed "pangenesis," suggesting miniature particles from all body parts were inherited. Aristotle countered this, emphasizing information transfer but incorrectly favoring the blending of parental contributions – an idea that persisted until Mendel. The invention of the microscope in the 17th century revealed sperm and egg cells, leading to debates between "preformationists" (believing a tiny preformed human resided in the sperm or egg) and "epigenesists" (arguing the embryo developed progressively).

The foundation of modern genetics was laid not in a major institute but in an Augustinian monastery garden. Between 1856 and 1863, Gregor Mendel conducted meticulous hybridization experiments with pea plants. He tracked discrete traits (like seed shape and flower color) across generations, quantifying inheritance patterns mathematically. Mendel deduced that inherited characteristics are determined by discrete units (later termed "genes"), existing in pairs (alleles), with one inherited from each parent. He formulated his Laws of Segregation (alleles separate during gamete formation) and Independent Assortment (alleles for different traits assort independently). Published in 1866, his work was largely ignored for over 30 years.

Mendel's groundbreaking insights were independently rediscovered in 1900 by Hugo de Vries, Carl Correns, and Erich von Tschermak. This sparked the rapid development of classical genetics. Walter Sutton and Theodor Boveri (1902-1903) recognized the parallel between Mendel's factors and the behavior of chromosomes during meiosis, proposing the Chromosome Theory of Inheritance, which stated genes reside on chromosomes. Thomas Hunt Morgan and his team, using the fruit fly (Drosophila melanogaster), provided compelling evidence for this theory. They discovered sex-linked inheritance (1910), mapped genes to specific chromosome locations, and demonstrated genetic linkage.

The focus then shifted to the chemical nature of the gene. Frederick Griffith's 1928 experiment with pneumococcal bacteria demonstrated a "transforming principle" capable of changing bacterial traits. Oswald Avery, Colin MacLeod, and Maclyn McCarty (1944) identified this principle as DNA (Deoxyribonucleic Acid). Confirmation came from Alfred Hershey and Martha Chase (1952) using radioactive labeling in bacteriophages. The race to understand DNA's structure culminated in 1953 when James Watson and Francis Crick, building on Rosalind Franklin's and Maurice Wilkins' X-ray crystallography data, proposed the iconic double helix model. This structure immediately suggested a mechanism for genetic replication and information storage, revolutionizing biology and ushering in the era of molecular genetics.