D.5: Phylogeny and Systematics

D.5.1: Outline Classification Called Systematics or classification –Based on common ancestry and natural relationships –Physical resemblance, behavior and ecological niche –Gives the ability to predict the behavior or niche of related organism Classification based on evolutionary evidence is called phylogenetic Classification is then used to construct a taxonomic key –Based on analogous or homologous structures –Allows one to identify an organism

D.5.2: Biochemical evidence of common ancestry Genetic code is universal –All organisms use the same genetic code to operate their cell(s) –Believed to be established early in history of life –Passed on by a common ancestry Biochemical paths –Similar process for photosynthesis and respiration between all organisms

D.5.3: Variations in specific molecules Possible to look at specific proteins to determine relationships –Hemoglobin alpha and beta chains are identical for both humans and chimps but differs in orangutans –Shows that humans and chimps are closer evolutionarily than humans and orangutans

D.5.4: Biochemical variation and evolutionary clock Evolutionary clock –Used to determine when two species diverged –Based on the number of differences between DNA or protein sequences Evidence that this works is that the number correlates with fossil evidence –Assumes that DNA replication rate is constant across species and time

D.5.5: Define Clade and cladistics Clade –A group of organisms sharing a single common ancestor and all the descendants of that ancestor –Based on DNA sequences, biochemical evidence and morphological data Cladistics –Method of constructing groups of clades –3 basic assumptions Change in characteristics occurs over time Any group of organisms is related by descent from a common ancestor There is a branching pattern of lineage-splitting with each split creating two groups

D.5.6: Analogous and Homologous Analogous structures –Structure or biochemical feature shared by unrelated organisms –Same basic function but their structure is different Homologous structures –Structure or biochemical feature shared between two or more organisms that share a common ancestor –Example is the pentadactyl limb

D.5.7: Constructing a cladogram Shows the relationship between clades The joints show homologous characteristics Moving from left to right the clades becomes smaller and the more homologous structures they share

D.5.9: Analyze a cladogram Start on the left and read to the right Left is earliest time and right is latest time Each branching shows where two groups diverged

D.5.10: Cladogram and classification Cladistics only recognize monophyletic groups –Groups that include a single common ancestor and all of its descendents Other groups are –Polyphyletic Do not include the common ancestor –Paraphyletic A group that includes the common ancestor but no all of the descendants