In 1902, Walter Sutton recognized that the way genes behaved during the production of gametes in peas, was identical to the way chromosomes behaved during meiosis. Among his observations were:
- Genes and chromosomes are both found in pairs.
- The alleles of a gene are distributed equally in gametes. Homologous chromosomes are also distributed equally in gametes.
- Genes and chromosome pairs both act independently.
These observations led Sutton to theorize that genes are actually located on chromosomes. Numerous studies by others in subsequent years provided further supporting evidence that genes are located on chromosomes. Finally, genetic studies on fruit flies provided convincing evidence that chromosomes carry genes. Sutton's observations were the basis for the chromosome theory of inheritance. The chromosome theory of inheritance states that chromosomes are composed of linear sequences of genes.