Chapter 26: Phylogeny and the Tree of Life

Objectives1. Identify how phylogenies show

evolutionary relationships.

2. Phylogenies are inferred based homologies and molecular data

3. Shared characters are the bases of phylogenetic trees

4. Genomes document an organism’s phylogenetic history

5. Molecular clocks help track evolutionary time

6. New information leads to refining our understanding of evolutionary history

Evolutionary Trees are based on Phylogenies

-Phylogeny is the evolutionary history of a species

-Taxonomy is the study that focuses on classification

-Use of a Hierarchy

- Uses of Binomial Nomenclature

-Started by Carl Linnaeus

Link between phylogenies and classification

Specifi

c Genera

l

Unresolved

Conclusions

1. No assumptions about time or genetic change ONLY on patterns of descent.

2. Can’t assume organisms evolved from the organism next to it only that they had a common ancestor.

Morphological Homologies and Analogies -In general the more similar morphologies the closer the species are related.-Analogous structures come from convergent evolution. (Similar environmental factors favor similar phenotypes)-Homologous structures have evolutionary link.

Molecular homologies are difficult to detect - Use of computer software to detect homologous areas of DNA

Cladistics: Systematics that uses common ancestry as primary way to classify organisms

Clade that includes ancstor and all its descendents.

Clade that includes descendents from two or more common ancestors

Clade that includes ancstor and some of its descendents.

Which is considered a shared ancestral character?

Which is considered a derived character?

What is the purpose of an outgroup?

Phylogenetic Trees are Hypothesis

So……?

Based on Maximum Parisomy or the least amount of evolutionary events measured by observed derived characteristics

Hypothesis allow for predictions about past and future

Genomic Homologies

Mainly caused by duplication, which allows for increased amount of biochemical opportunities

1. Orthologous Genes: Homologous genes found in different species

2. Paralogous Genes: Gene duplication within a species

Genome Comparison

1. 99% of human and mice genomes are Orthologous

2. Phenotypic changes seem to increase at a faster rate then the duplication rate.

Molecular Clocks

1. Measurement of time that relies on the constant rates of gene evolution.

2. The longer ago the divergence time the more mutations have occurred

3. Can be used to date the origin of diseases like HIV (p. 551)

Understanding of life and classification has changed based on new knowledge

-Euglena-Prokaryotic differences

Horizontal GeneTransfer-Gene transfer through other methods such as viral infection or fusion of organisms