Boveri–Sutton chromosome theory

The Boveri-Sutton chromosome theory (also known as the chromosome theory of inheritance) is a fundamental unifying theory of genetics which identifies chromosomes as the carrier of genetic material. It correctly explains the mechanism underlying the laws of Mendelian inheritance by identifying chromosomes with the paired factors (particles) required by Mendel's laws. It also states that chromosomes are linear structures with genes located at specific sites along them.

It states simply that chromosomes, which are seen in all dividing cells and pass from one generation to the next, are the basis for all genetic inheritance.

Background
Theodor Boveri and Walter Sutton independently developed the chromosome theory of inheritance in 1902. Boveri was studying sea urchins, in which he found that all the chromosomes had to be present for proper embryonic development to take place. Sutton's work with grasshoppers showed that chromosomes occur in matched pairs of maternal and paternal chromosomes which separate during meiosis.

In 1879 Walther Flemming had discovered chromosomes and mitosis in salamander eggs. August Weismann then discovered meiosis in the germ cells, and linked this with Mendelian inheritance in his germ plasm theory. This proposed the Weismann barrier, which prevented germ line reproductive cells from passing on adaptive traits acquired by somatic cells during an organism's life, ruling out Lamarckian inheritance. Boveri and Sutton incorporated this correct idea into their reasoning. However, Weismann did not identify the meiotic chromosomes as Mendel's factors of inheritance.

Verification
The proposal that chromosomes carried the factors of Mendelian inheritance was initially controversial, but in 1913 it gained strong support when Eleanor Carthers documented definitive evidence of independent assortment of chromosomes in a species of grasshopper. Debate continued, however, until 1915 when Thomas Hunt Morgan's work on inheritance and genetic linkage in the fruit fly Drosophila melanogaster provided incontrovertible evidence for the proposal.