Chsomosomal theory of inheritance:

This illustration is given to explain the Mendal’s principle of independent assortment. In terma of movement of chromosomes during meiosis.

1) Mendal work could not be widely published in his time.

2) And also his concept of genes as stable and discrete units did not ‘blend’ with each other, was not accepted by contemporaries 

3) Thirdly, Mendel’s approach of using mathematics to explain biological phenomena was totally new and unacceptable.

4) In 1900, three Scientists (de Vries, Correns and von Tschermak) independently rediscovered Mendel’s results on the inheritance of characters.

5) Due to advancements in microscop , chromosomes were discovered and their  movement during meiosis also worked out.
6) Walter Sutton and Theodore Boveri noted that the behaviour of chromosomes was parallel to the behaviour of genes and used chromosome movement to explain Mendel’s laws. They also argued that the pairing and separation of a pair of chromosomes would lead to the separation of a pair of factors they carried.

7) Sutton united the knowledge of chromosomal segregation with Mendelian principles and called it the
chromosomal theory of inheritance.
 

Experimental verification of the chromosomal theory of inheritance by Thomas Hunt Morgan:

Morgan and his colleagues, led to discovering the basis for the variation that sexual reproduction produced. Morgan worked with the tiny fruit flies, Drosophila melanogaster, which were found very suitable for such studies.

1) They could be grown on simple synthetic medium in the laboratory.

2) They complete their life cycle in about two weeks, and a single mating could produce a large number of progeny flies.

3) Also, there was a clear differentiation of the sexes – the male and female flies are easily distinguishable.

4) Also, it has many types of hereditary variations that can be seen with low power microscopes.

5) For example Morgan hybridised yellow-bodied, white-eyed females to brown-bodied, red-eyed males and intercrossed their F1 progeny. He observed that the two genes did not segregate independently of each other and the F2 ratio deviated very significantly from the 9:3:3:1 ratio.