Independent Origins
Volvox; refered to as a colony by certain researchers
- Multicellular organisms with differentiated cells originated multiple times
- Red, green, and brown algae arose independently from each other
- Ex:
VOLVOX - multicellular green algae with two differentiated cells
CHLAMYDOMONAS - unicellular, cell homologous (similar) to those of Volvox
- Suggests that transition from unicellularity to multi- can result from changes in how existing genes are used (does not require origin of novel genes)
25.2 Multicellularity has Originated
Several Times in Eukaryotes
novel gene: gene that has never been identified as a gene before ("new")
Multicellular Colonies
The fact that organisms originated multiple times allows us to compare and contrast how independent groups were originated
- 1st multicellular forms (occur early in fossil record and also remain common today)
- Colonies: collections of cells that are connected to one another but show little or no cellular differentiation (specialization)
- Found in eukaryotic lineages whose members have rigid cell walls and some who do not
- The former remain attached by shared cell walls
- Latter held together by proteins that connect to each other
Steps in the Origin of Multicellular Animals
Multicellular Volvox compared to unicellular Chlamydomonas
- Protist groups closely related to animals serve as information to help track origin
- Origin of multicellularity required evolution of cells - adhering and signaling each other
- Research - Identifying specific proteins that played roles in origin
True: Origin resulted from co-opting genes used for a different purpose (or converting existing genes to have different uses)
False: Origin resulted from evolution of a "toolkit" made of novel genes