Sex chromosomes were first studied by

Chromosomes that are involved in sex determination of an organism are called sex chromosomes. The X and Y chromosomes, the sex chromosomes in mammals including human, were first discovered in beetles by Nettie Stevens in 1906. She observed presence of identical looking pairs of each of several chromosomes in female beetles and that of one pair with two morphologically different chromosomes in female beetles. She termed these two chromosomes the X and the Y, and found that female beetles differed from males in containing two X chromosomes. Humans also follow XX-XY mechanism where females are XX and males are XY. Correct option is C.
Castle studies chromosomal basis of sex determination; McClung 1902 reported presence of two types of gametes in male grasshopper (XO); Correns rediscovered Mendel's principals of inheritance while working on incomplete dominance of flower colour in Mirabilis jalapa. Correct option is C.