Which of the following pairs is wrongly matched?

Which of the following pairs is wrongly matched?

Option 1 : T.H. Morgan                                                   :      Linkage

Option 2 : Starch synthesis in pea                                :      Multiple alleles

Option 3 : XO types sex determination                         :      Grasshopper

Option 4 : ABO blood grouping                                     :      Co-dominance

Correct answer is option 2.