Which of the Following is an Example of a Metazoan

Question

Which of the following is an example of a metazoan (animal) innovation? A) 24TM Na⁺ channels B) 24TM Ca²⁺ channels C) 6TM K⁺ channels D) 2TM K⁺ channels E) None of the above

Accepted Answer

6TM and 2TM K⁺channels are found in prokaryotes as well as eukaryotes. Single-cell yeast and green algae have 24TM Ca²⁺ channels. Recently, single-celled eukaryotes called choanoflagellates have been found to have homologs of 24TM Na⁺ channels, suggesting that duplication of the 24TM Ca²⁺ channel gene occurred prior to the emergence of nervous systems.