The accessory chromosome explanation was proposed by

Solution (By Examveda Team)

The accessory chromosome explanation was proposed by Mc clung.
Clarence Erwin McClung was an eminent American zoologist and prairie pioneer cytologist who discovered the role of chromosomes in sex-determination.
In 1901 McClung hypothesized that sex determination in grasshoppers is dependent upon the number of X chromosomes within a cell. Maleness in grasshoppers is determined by the absence of a second X chromosome (XO), while femaleness is induced by the presence of two X chromosomes (XX). This theory helped to prove that chromosomes carry genetic information that determines phenotype.