Final answer:
Physical linkage via a 2 loci cross was first proposed by Bateson and Punnett in 1900, leading to the identification of genetic linkage. It was further substantiated by Morgan, Sturtevant, McClintock, Creighton, and Stern through a series of experiments with pea plants, corn, and fruit flies, which reinforced the Chromosomal Theory of Inheritance and introduced genetic mapping.
Step-by-step explanation:
The concept of physical linkage via a 2 loci cross was a major discovery in the field of genetics, primarily attributed to the early 20th-century geneticists William Bateson, and Reginald Punnett who first proposed the idea of linkage in 1900. Their work involved crossing pea plants with different traits and observing inheritance patterns that did not align perfectly with Gregor Mendel's laws of independent assortment, suggesting that some genes are linked on chromosomes and are inherited together. However, it was Thomas Hunt Morgan and his student Alfred Sturtevant, working with fruit flies (Drosophila melanogaster), who provided significant experimental evidence for this theory and developed methods like genetic mapping to study linkage and recombination further.
In 1911, Morgan and Sturtevant began systematic studies of genetic linkage and distances, laying the groundwork for the creation of the first genetic maps. Subsequently, in 1931, the concept was vividly demonstrated by Barbara McClintock and Harriet Creighton in corn plants, as well as by Curt Stern in Drosophila, showing the physical evidence of chromosome crossover during meiosis. Through meticulous breeding experiments and microscopic analysis of chromosome structure, these scientists confirmed that linked genes could undergo homologous recombination, providing a molecular mechanism for genetic inheritance and variability.