What evidence supports the Ohno suggestion about vertebrate evolution from ancestral invertebrates by whole-genome duplication?

Question

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Ohno suggested that ancestral invertebrates underwent whole-genome duplication, which resulted in doubling of the number of genes in the genome. This event led to the evolution of vertebrates. The evidence supporting this suggestion includes the fact that modern vertebrates have four times the number of certain groups of genes compared to their homologues in Amphioxus, which is considered an invertebrate chordate closely related to the ancestral form. This suggests that a whole-genome duplication event occurred during vertebrate evolution, resulting in the increased number of genes. Choices B, C, D, and E are incorrect because they do not accurately reflect the evidence supporting Ohno's suggestion.

What Evidence Supports the Ohno Suggestion About Vertebrate Evolution from Ancestral