To solve this problem, we need to identify the sub-stage of prophase I in meiosis where recombination nodules appear. Let's analyze the stages of prophase I:$\newline \bullet$Leptotene: This is the first stage of prophase I where chromosomes begin to condense and become visible as long threads.$\newline \bullet$Zygotene: During this stage, homologous chromosomes start pairing in a process called synapsis, forming synaptonemal complexes.$\newline \bullet$Pachytene: This is the stage where recombination nodules appear. These nodules are protein structures that facilitate genetic recombination or crossing over between homologous chromosomes.$\newline \bullet$Diplotene: In this stage, the synaptonemal complex dissolves, and homologous chromosomes start to separate, but remain connected at chiasmata where crossing over occurred.$\newline \bullet$Diakinesis: This is the final stage of prophase I where chromosomes are fully condensed and prepared for metaphase I.$\newline$Based on this analysis, recombination nodules appear during the pachytene stage of prophase I.$\newline$Therefore, the correct option is Option 2: Pachytene.