In one of the experiments described in Module 18.13, researchers tested the hypothesis that the highly successful arthropod body plan resulted from new genes that originated in the arthropod lineage. Draw a diagram showing the evolutionary relationship between arthropods and velvet worms and use it to explain why velvet worms were a good choice to test this hypothesis. What results would have supported the hypothesis?

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Step 1: Begin by understanding the evolutionary relationship between arthropods and velvet worms. Arthropods (e.g., insects, crustaceans, spiders) and velvet worms (Onychophora) share a common ancestor, making velvet worms a close relative of arthropods. This evolutionary proximity makes velvet worms a good comparison group for studying genetic innovations specific to arthropods.

Step 2: Draw a simple phylogenetic tree to visually represent the evolutionary relationship. Start with a common ancestor at the base, then branch into two groups: one leading to arthropods and the other leading to velvet worms. Label the branches clearly to show the divergence.

Step 3: Explain why velvet worms were chosen for the experiment. Since velvet worms are closely related to arthropods but lack the highly specialized body plan of arthropods, they serve as a baseline for identifying genes that are unique to arthropods and potentially responsible for their evolutionary success.

Step 4: Describe the experimental approach. Researchers would compare the genomes of arthropods and velvet worms to identify genes that are present in arthropods but absent in velvet worms. These genes could be candidates for driving the development of the arthropod body plan.

Step 5: Discuss the expected results that would support the hypothesis. If the hypothesis is correct, researchers would find new genes in arthropods that are absent in velvet worms. These genes would likely be involved in processes such as segmentation, exoskeleton formation, or other features unique to arthropods. Additionally, functional studies of these genes could show their role in the development of the arthropod body plan.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Evolutionary Relationships

Evolutionary relationships illustrate how different species are related through common ancestry. In this context, a phylogenetic tree can be used to depict the lineage of arthropods and velvet worms, highlighting their shared ancestry and divergence. Understanding these relationships is crucial for evaluating hypotheses about evolutionary adaptations and the emergence of new traits.

Gene Origin and Evolution

The concept of gene origin and evolution refers to how new genes can arise through various mechanisms, such as gene duplication, mutation, and horizontal gene transfer. In the context of the hypothesis, researchers are investigating whether unique genes in arthropods contributed to their successful body plan. Identifying these genes and their evolutionary history is essential for understanding the genetic basis of evolutionary innovations.

Hypothesis Testing in Biology

Hypothesis testing in biology involves formulating predictions based on a hypothesis and designing experiments to validate or refute these predictions. In this scenario, results supporting the hypothesis would include evidence of unique gene presence in arthropods that are absent in velvet worms, indicating that these genes contributed to the arthropod body plan. This process is fundamental to scientific inquiry and helps establish causal relationships in evolutionary biology.