Explanation

Thomas Hunt Morgan and his students (like Bridges) demonstrated that genes are linked on chromosomes, but Mendel's work established independent assortment. However, the specific phrasing 'discounted' usually refers to how Sutton and Boveri proposed the chromosome theory, while Morgan provided the experimental proof linking genes to chromosomes. Wait, let's re-read carefully. 'Linkage of hereditary units was discounted by...' This is a poorly phrased question. Usually, linkage was discovered by Morgan. Mendel didn't know about linkage. Sutton and Boveri proposed the chromosome theory. The question likely implies who showed that traits are linked on chromosomes or who challenged the idea of independent assortment? Actually, 'discounted' might mean 'disproved' or 'challenged'. But linkage is a real phenomenon. Perhaps it means 'Who discovered linkage?' No, 'discounted' is weird. Let's look at standard MCQs for this topic. Often, questions ask who proposed the chromosome theory of inheritance (Sutton and Boveri). Or who discovered linkage (Morgan). If the question means 'Who showed that genes are linked on chromosomes?', it's Morgan. If it means 'Who proposed that hereditary units are located on chromosomes?', it's Sutton and Boveri. The option A has typos ('Batson', 'Pun net'). Option B has 'T.B. Morgan'. Morgan is the father of linkage studies. He showed that linked genes do not assort independently, thus 'discounting' Mendel's law of independent assortment for linked genes? Or perhaps the question is garbled and means 'Who discovered linkage?' In that case, Morgan is the key figure. Option B includes Morgan. Option A is nonsense due to typos. Option C has Sutton (correct for chromosome theory) but Porter is wrong (should be Boveri). Option D has Bridges (Morgan's student, confirmed chromosomal basis of inheritance) and Shull (hybrid corn). The most likely intended answer in flawed MCQs about linkage is Morgan. Therefore, B is the best choice despite the 'discounted' wording being awkward.