Chapter 2, Problem 33P

Recall that Mendel obtained pure-breeding with either long or short stems and those hybrids had long stems (Fig. 2.8). Monohybrid crosses produced in F₂ generation with a 3:1 ratio of long stems to short stems, indicating that this difference in stem length is governed by a single gene. The gene that likely controlled this trait in Mendel’s plants has been discovered, and it specifies an enzyme called G3βH, which catalyze the reaction shown in the accompanying figure. The product of the reaction, gibberellins, is a growth hormone that makes plants grows tall. What is the most likely hypothesis to explain the difference between the dominant allele (L) and recessive allele (l)?