Chromosomal theory of inheritance was based on
A. Segregation of genes.
B. Diploidy and haploidy.
C. Sex linkages.
D. Presence of sex chromosomes.

Hint: Boveri and Sutton were the ones to come up with the chromosomal theory of inheritance which states that genes are found at some particular locations on the chromosomes, they also said that the behavior of chromosomes throughout the process of meiosis will make an explanation for Mendel’s laws of inheritance.

Complete step by step answer: Sutton and Boveri in the year 1902 by correlating what Mendel had concluded came up with the chromosomal theory of inheritance based on how chromosomes behave during mitosis and meiosis.
1. They said chromosomes are present in pairs.
2. The chromosomes which are homologous tend to separate during meiosis so that alleles can get separated or segregated.
3. Genes are present on chromosomes.
4. During fertilization, the chromosomal pair is retained.
This formed the basis of the Chromosomal theory of inheritance.
Hence, Option A- Segregation of genes the correct answer.
Additional Information:
Thomas Morgan along with his students explained the whole genetic theory on fireflies with proper evidence for his explanation. He tried explaining the mutations in the color of the eyes of a firefly. This brought about huge progress in the field of genetics to study and locate every gene on the chromosome and determine the difference between the genes of a male and female. The logic that chromosomes and hereditary might be linked or connected to one another became even more clear after the experiment performed by Theodor Boveri and Walter Sutton. However, Thomas Hunt Morgan's experiments with fruit flies confirmed it.

Note: The chromosomal theory of inheritance isn’t the discovery made by one scientist instead it is because several scientists worked upon it and gave their theories one scientist was able to combine parts from those various theories to get the chromosomal theory of inheritance.