Answer: The correct answer for the blank is- Chromosome theory.
Chromosome theory was proposed by Boveri and Sutton, which states that genes are located at specific locations on chromosome and chromosome is considered as the genetic material, involved in Mendelian inheritance pattern.
During the process of meiosis ( gamete formation in sexually reproducing organisms), pair of homologous chromosomes segregate as discrete units and are independent of other pair of chromosomes.
Thus, chromosome theory is the right answer.