[Campbell Biology P.725] The genomic comparisons between Monosiga brevicollis and animals, p... | Practice Question
The genomic comparisons between Monosiga brevicollis and animals, particularly regarding cadherin proteins, strongly suggest which of the following about the evolution of animal multicellularity?
A: Animal multicellularity arose from a completely independent evolutionary path, with no genetic links to unicellular organisms like choanoflagellates.
B: Key steps in the transition to animal multicellularity involved the repurposing and rearrangement of existing protein domains found in choanoflagellates, alongside the incorporation of novel domains.
C: Choanoflagellates are direct descendants of the earliest multicellular animals, having simplified their cellular structure over time.
D: The presence of 78 animal-like protein domains in M. brevicollis proves that choanoflagellates are themselves multicellular organisms.
Explanation
The text explains that M. brevicollis has many protein domains otherwise only known in animals. It specifically discusses how animal cadherin proteins, crucial for multicellular functions, derive from ancestral choanoflagellate domains with the addition of the 'CCD' domain. This supports the idea that existing genetic components were adapted and combined in new ways for multicellularity.