Chromosome theory of inheritance was proposed by

In Mendel's and Darwin's time, the chromosomal theory of inheritance was unknown. Sutton and Boveri were the ones who proposed it.

Walter Sutton's articles from 1902 and 1903, as well as separate work by Theodor Boveri around the same time, are credited with the chromosomal hypothesis of heredity.

So, option A is the correct answer.

Option A : Sutton and Boveri independently.