Transcript Constructing and Using Phylogenies

Human Impact on the Evolution of the Cheeta!!
Chapt. 22:
“Constructing and Using Phylogenies”
One Species from Another!!
I DON”T BELIEVE IT!!
Systematics-- the study of the evolutionary relationships of organisms;
relationships of present-day organisms with the past.
How can we tell what species came from another?
What species are more closely related than others?
What species will persist into the future?
Taxonomy- the classification of different species
Taxon- a unit in a classification system
Carolus Linnaeus- the binomial nomenclature system
I.e. Genus, species-- Homo sapiens
Binomial Nomanclature:
Genus name is capitalized, species name is not, both are italicized.
e.g. Escherichia coli, Drosophila melangaster, Agropyron smithii
(also E. coli, D. melangaster, Agropyron spp.or sp.)
Hierarchical Classification (order of taxons in the Linnaean system):
Species--Genus--Family--Order-- Class--Phylum--Kingdom
(see Fig. 22.2 for the moss rose, Rosa gallica)
Systematics:
(1) Determine evolutionary relationships and express them in
phylogenetic (family) trees
(2) Express evolutionary relationships in a classification system
What is the “true” phylogeny of a particular group of organisms?
Evidence: fossils (extinct) and living (extant) organisms
Cladistics and cladograms-- evolutionary trees; points at which
branches occur, respectively
Clade- a complete portion of the phylogeny that comes from
a common ancestor
Phylogenetic tree- cladogram with dates of branches; common
ancestor at bottom (Fig. 22.6)
Systematists must determine ancestral (original) versus
derived (changed from original) traits
Special versus General homologous traits-- shared by a few vs.
shared by many
To construct a cladogram-(1) select group of organisms
(2) choose traits to compare
(3) determine if they are ancestral or derived
Most challenging task of a cladogram- recognizing divergence
versus convergence in ancestral traits, e.g. homlogous
structures (cactus spines and bat/bird wing).
PROBLEM: Homoplasy = convergent evolution of same trait more
than one time (e.g.modified leaves and analogous wings of insects
and birds, Fig. 22.4). Homologies from Analogies, Fig. 22.5)
Outgroups- a group branches off due to Special
homologous traits, but still have General
homologous traits in common
Table 22.1 and Fig. 22.6-- Derived traits in vertebrates and a probable
cladogram.
I.e. jaws, lungs, claws/nails all derived traits;
feathers and fur (birds/mammals) derived from
claws and nails (reptiles).
MICROEVOLUTION-- alleles change = changes in DNA & proteins
(Review Chapt. 12)
Molecular Evolution and Phylogeny-- ancestry and cladograms based
on differences in proteins and nucleic acids (RNA and DNA),
no longer just gross morphology
e.g. all land plants have 100 genes for making RNA to control
synthesis of photosynthetic enzyme production
DNA Hybridization-- mix DNA of two species--denatured
--reassociated-- degree of reassociation =
closer ancestry (Humans and chimpanzees,
1.6 % difference in DNA sequences; cow/pig = 20%)
Table 22.2 and Fig. 22.9 (panda bear ancestry;
dogs split with racoons-pandas-bears)
Figure 22.10, Horseshoe crab evolution from over 600 mya !!
Figure 22.13, Phylogeny of the Domains and Kingdoms
Where are the fungi in terms of being a plant or animal?