Classification of Living Things

2 Taxonomy: Distinguishing Species Distinguishing species on the basis of structure can be difficult  Members of the same species can vary in structure  Attempts to demonstrate reproductive isolation is problematic because: ­Some species hybridize, and ­Reproductive isolation is difficult to observe

3 Members of a Species??

4 Hybridization between species

Classification of Living Things What makes a species?!? Species (def): a class of individuals having some common characteristics or qualities; distinct sort or kind. the major subdivision of a genus of subgenus, regarded as the basic category of biological classification composed of related individulas that resemble one another able to breed among themselves, but are not able to breed with members of another species 5

Classification of Living Things 6 Phylogenetic Trees Systematics - the diversity of organisms at all levels One goal of systematics is to determine phylogeny (evolutionary history) of a group Phylogeny often represented as a phylogenetic tree  A diagram indicating lines of descent  Each branching point: ­Is a divergence from a common ancestor ­Represents an organism that gives rise to two new groups

7 Classification and Phylogeny

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Classification of Living Things 9 Phylogenetic Trees Classification lists the unique characters of each taxon and is intended to reflect phylogeny  Primitive characters: ­Present in all members of a group, and ­Present in the common ancestor  Derived characters: ­Present in some members of a group, but ­Absent in the common ancestor

Classification of Living Things 10 Classification and Phylogeny

Classification of Living Things In terms of divergence, which one of these is not like the other? Top, Middle or Bottom?? 11

Classification of Living Things 12 Tracing Phylogeny Fossil Record  Fossil record is incomplete  It is often difficult to determine the phylogeny of a fossil Homology  Refers to features that stem from a common ancestor  Homologous structures are related to each other through common descent Analogy  Similarity due to convergence

13 Ancestral Angiosperm

Classification of Living Things 14 Tracing Phylogeny Convergent Evolution  The acquisition of a feature in distantly related lines of descent  The feature is not present in a common ancestor Parallel Evolution  The acquisition of a feature in two or more related lineages  The feature is not present in a common ancestor

15 Convergent Evolution

Classification of Living Things 16 Molecular Data Protein Comparisons  Immunological techniques ­Degree of cross reaction used to judge relationship  Amino acid sequencing ­Similar sequence in same protein indicates close relationship RNA and DNA Comparisons  Systematics assumes: ­Two species with similar base-pair sequences are assumed to be closely related ­Two species with differing base-pair sequences are assumed to be only distantly related Molecular Clocks  Use non adaptive nucleotide sequences  Assumed constant rate of mutation over time

17 Ancestry of Giant Pandas??

18 Molecular Data

Classification of Living Things Molecular clocks provide clues to evolutionary history.

Classification of Living Things A quick review of gene expression

Classification of Living Things

Molecular clocks use mutations to estimate evolutionary time. Mutations add up at a constant rate in related species.  This rate is the ticking of the molecular clock.  As more time passes, there will be more mutations.

Classification of Living Things Another ten million years later— one more mutation in each lineage Ten million years later— one mutation in each lineage Molecular clocks use mutations to estimate evolutionary time. DNA sequence from a hypothetical ancestor The DNA sequences from two descendant species show mutations that have accumulated (black). The mutation rate of this sequence equals one mutation per ten million years. Mutations add up at a fairly constant rate in the DNA of species that evolved from a common ancestor.

Classification of Living Things Scientists estimate mutation rates by linking molecular data and real time. –an event known to separate species –the first appearance of a species in fossil record

Classification of Living Things Different molecules have different mutation rates. –higher rate, better for studying closely related species –lower rate, better for studying distantly related species Mitochondrial DNA and ribosomal RNA provide two types of molecular clocks.

Classification of Living Things Mitochondrial DNA is used to study closely related species. grandparents parents child Nuclear DNA is inherited from both parents, making it more difficult to trace back through generations. Mitochondrial DNA is passed down only from the mother of each generation,so it is not subject to recombination. mitochondrial DNA nuclear DNA –mutation rate ten times faster than nuclear DNA –passed down unshuffled from mother to offspring

Classification of Living Things Ribosomal RNA is used to study distantly related species. –many conservative regions –lower mutation rate than most DNA

28 The Three-Domain System of Classification

29 The Three Domains of Life