[Campbell Biology P.755] Based on Figure 33.29, if Acanthokara kaputensis had not possessed ... | Practice Question

Based on Figure 33.29, if Acanthokara kaputensis had not possessed the Ubx and abd-A Hox genes, how would the conclusions of the study regarding arthropod body plan evolution be affected?

  • A: The conclusion that Ubx and abd-A genes were not related to the evolution of increased body segment diversity in arthropods would be strengthened.
  • B: The hypothesis that Ubx and abd-A genes drove the evolution of body segment diversity in arthropods would be supported, as their absence in a closely related outgroup would suggest their novelty in arthropods.
  • C: The study would still conclude that the evolution of increased body segment diversity in arthropods was unrelated to new Hox genes, but the evidence would be weaker.
  • D: The study would become inconclusive, as the presence or absence of these genes in *Acanthokara kaputensis* is irrelevant to the evolution of arthropod body plans.

Explanation

The original hypothesis stated that the Ubx and abd-A Hox genes drove the evolution of body segment diversity in arthropods and arose on the arthropod branch. The experiment tested this by looking for these genes in onychophorans, a closely related outgroup. The actual result found the genes were present in onychophorans, leading to the conclusion that the genes predated the arthropod/onychophoran split, and thus new Hox genes were not the cause of increased segment diversity in arthropods. If, however, Acanthokara kaputensis had not possessed these genes, it would have supported the original hypothesis, suggesting that these genes indeed arose after the split from onychophorans and were novel to arthropods, thus driving their segment diversity.