PHYLOGENY AND EARLY LIFE Flashcards
When did the first prokaryotes show up?
3.5 bya
When did the first eukaryotes show up?
~1.8 bya
What led to the evolution of eukaryotes?
Endosymbiosis, the theory that a prokarytic cell engulfed a smaller cell which would later evolve into an organelle found in eukaryotes
When did multicellularity appear?
Early multicellular eukaryotes appeared 1.2 bya - smaller multicellular eukaryotes appeared 1.8 bya and larger, diverse multicellular eukaryotes appeared 600 years ago
What are the benefits to multicellularity?
- Larger in size
- Prey to fewer predators
- Longer life
- Not restricted to the lifespan of a single cell
- Specialization
- Increases efficiency
How do multicellular cells stay attached?
Cadherins, or glycoproteins in cell-cell adhesion, which are crucial in development
When was land colonized?
Cyanobacteria and other photosynthetic eukaryotes coated terrestrial surfaces over 1 bya
Animals, plants, and fungi didn’t colonize until 500 mya
When did primates show up?
6-7 mya
What was the Cambrian Explosion?
Prior to the Cambrian Explosion, large organisms were soft-bodied and there was little evidence of predation
After the explosion, defensive adaptations began to arise
What is phylogeny?
Phylogeny is the evolutionary history of a species/group of species
What is the hierarchial classification?
Domain, kingdom, phylum, class, order, family, genus, species
What is a problem with the Linnaean system
Species may be places into a genus to which it may not be closely related. It distinguishes groups but does not tell about the group’s evolutionary relationship to one another
What are phylogenetic trees used for?
Phylogenetic trees represent a hypothesis about evolutionary relationships, and are depicted as a series of dichotomies, or 2-way branching points
What are sister taxa?
Sister taxa are groups of organisms which share an immediate common ancestor that is not shared with another group
What are problems with the phylogenetic tree?
- Shows patterns of descent but not phenotypic similarities
- Cannot infer ages
- Shouldn’t assume that a taxon evolved from the taxon next to it
What does a clade consist of?
A clade consists of ancestral species and their descendents
What is a monophyletic group?
A monophyletic group (“single tribe”) consists of ancestral species and all its descendents
What is a paraphyletic group?
A paraphyletic group (“beside the tribe”) consists of an ancestral species and some, but not all, descendents and the most recent common ancestor
What is a polyphyletic group?
A polyphyletic group (“many tribes”) consists of distantly related species but does not include the most common ancestor
What is adaptive radiation?
Adaptive radiation occurs when a common ancestor divides into multiple species with time which are adapively specialized to a specific environmental niche
What is divergent evolution?
Divergent evolution is the development of a new species fro a pre-existing species
What is convergent evolution?
Convergent evolution is the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
What are ancestral traits?
Ancestral traits are traits inherited from a common ancestor and have undergone little change since
What are derived traits?
Derived traits are present in that organism but are absent in the last common ancestor
