Cladistics & Trees (L2+3)

Darwinisim

a mechanism not a history, tells us the how and not the what of evolutionary history

Natural selection

acts on the phenotype

Ernst Haeckel

drew the first monophyletic tree of all life on Earth (all organisms share a single common ancestor)

Evidence of shared ancestor

universal genetic code (genes work the same), characters shared by two species existed in their common ancestor

Monophyletic group (Clades)

a single common ancestor and all descendants of the last common ancestor are in the group

Paraphyletic group

does not include all descendants of the last common ancestor (reptiles do not include birds)

Polyphyletic group

groups that have more than one origin

Outgroups

groups that are not part of a monophyletic group

Sistergroup

groups that can be combined to form a monophyletic group

Cladogram

diagram that represents the branching pattern of evolution and shows the relationship between species

Phylogram

like a cladogram but branch lengths show how much evolution has occurred between species

Principle of Parsimony (Occam’s Razor)

the simplest explanation is the right one

Homologous characters (Homologs)

inherited by two species from their ancestor

Analogous characters (Analogs)

evolved independently more than once (fin of sharks and dolphins) due to convergent evolution

LECA → Opisthokonta →

Choanozoa → Metazoa → Eumetazoa → Bilateria → Deuterostomia → Chordata → Craniata → Vertebrata → Gnathostomata → Osteichthyes → Sarcopterygii → Tetrapoda → Amniota → Synapsida → Mammalia → Eutheria → Eurarchontoglires → Primates → Homo sapiens

Multicellularity

evolved multiple times in different clades (almost all eukaryotic groups are single-celled)

Plesiomorphy (primitive character)

ancestral character shared by all members of a clade that does not distinguish the clade from other clades

12 amino acid insertion

in the f1 gene; found in Opisthokonts (unlikely to be analogous)

Gene fusion

of EGF and TK in choanoflagellates and animals (shows they are closely related)

Use of base sequence

to determine relation when there are no obvious morphological characters

Opisthokonts

flagellate cells that propel themselves with a single posterior flagellum

Synapomorphy

apomorphy shared by two or more taxa that can be thought of as evolutionary homologs

Apomorphy

novel character evolved from its ancestral form