Coupling time to molecular phylogenies

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Coupling time to molecular phylogenies Assumption
constant mutation rate
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Example primate evolution
Individual genes have individual rates of
change within and between species. Constant
mutation rates are approached by using average
numbers of changes.
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Molecular techniques have power cichlid fishes
What is the basis of these differences? Lake
Victoria dry 12,400 ybp 500 cichlid species
Generic level
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Gene regulation and evolution
Signal transduction in which an extracellular
signal protein to an transmembrane receptor
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Things to consider

• Many proteins are shared by evolutionarily
  diverse groups.
• Therefore, as was seen for morphogenic bone
  protein (MBP)??????
• many evolutionary changes are based on
• controlling the expression of shared (homologous)
  genes
• At different times
• For different lengths of time
• In different tissues.

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Evolution of Regulatory Sequences

• Genomes of humans and chimpanzees have been
  completely sequenced.
• DNA sequences for homologous protein coding genes
  differ by c. 1.
• Comparison of all homologous proteins, a mean
  difference on only 2 amino acids.
• At the level of DNA and amino acid sequences,
  humans and chimps are extremely similar.
• Therefore, why are humans and chimps so different
  phenotypically?
• Hypothesis there must be differences in the
  timing and degree of gene expression.

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• Regulatory genes code for transcription factors
  and other proteins that bind to DNA or to other
  proteins.
• Regulatory sequences binding sites of
  transcription factors.
• Interact to
• 1. turn structural genes on or off
• 2. to increase or decrease the activity of
  structural genes
• An example of a regulatory change that changed
  the phenotype is found in the plant family
  Solanaceae.

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A change in a MADS-box regulator sequence
produced an evolutionary change.
Potatoes lack post-pollination sepal growth.
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• MPF2 is a transcription factor gene in potatoes
  and ground cherries.
• Stimulates cell division.
• Expressed in vegetative tissue in potatoes in
  vegetative AND floral tissue in ground cherries.
• Chinese lantern structure does not form if MPF2
  is knocked out experimentally.
• Hypothesis
• Mutation of MPF2 gene
• Modified MPF2 protein
• Modification of developmental pathway
• Change to continued sepal growth
• Production of the capsule surrounding the fruit.

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Evo-Devo Evolution and Development
Dll expression
En/Inv expression
Eyespots on a butterfly wing
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Homeotic Genes and Animal Body Plans

• Multicellular animals develop in four dimensions.
• 3 spatial time
• Each cell has to have
• 1. spatial information where it is relative to
  other cells
• 2. temporal information what is occurring in the
  developmental sequence.
• Homeotic genes (Hox genes) (1)transcription
  factors determine which (2) structural genes are
  activated to produce (3) particular structures.

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Some cells or tissues located along the major
body axes assume positional information during
development
(After Strickberger.)
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Hox genes in Drosophila (body segmentation) Occur
in clusters (gene duplication) Positional
information
Where genes are expressed

Colinearity 1. Expressed first 2. Anterior to
posterior 3. Greater quantity of transcription
factors
Gene location in hox cluster
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Hox Genes

• Basis of colinear Hox gene expression
• Hox genes provide information on location.
• 1. The transcription factor from the 3 end
  required to express all downstream Hox genes.
• 2. The TF effectiveness in initiating upstream
  gene expression declines with distance.
• Each Hox gene contains a highly conserved 180 bp
  sequence the homeobox.
• Codes for a DNA binding segment (aa sequence) in
  the transcription factor.
• The transcription factors activate other genes.
• These genes produce structures appropriate for
  that location.
• Mutations in Hox genes result in inappropriate
  structures for that location.

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Hox gene products activates genes responsible for
making a particular structure.
Mutations in Hox genes bx, pbx, and abx
Mutation of Hox gene antp
Wings normally appear on T2 Hox mutations change
identity of T3 cells to T2 cells. Ancestors of
dipteran flies had 4 wings.
Identity of a head segment changed to that of a
thoracic segment