Which of the following pairs is wrongly matched?

Starch synthesis in pea seeds is controlled by a single gene. It has two alleles (B and b) that exhibit incomplete dominance. ‘BB’ homozygotes produce large starch grains. In contrast, ‘bb’ homozygotes produce smaller starch grains. Heterozygotes (Bb) produce starch grains of intermediate size. 

(2) AB blood type is an example of codominance. 

(3) X0 sex determination is found in grasshoppers.

(4) T.H. Morgan discovered linkage in Drosophila melanogaster.