Evolution of Regulatory Sequences

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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 of only 2 amino acids.
• At the level of DNA and amino acid sequences,
  humans and chimps are extremely similar.
• ? 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 affect gene expression.
• Regulatory sequences DNA binding sites of
  transcription factors.
• Interaction to
• 1. turn structural genes on or off
• 2. increase or decrease the activity of
  structural genes
• A macroscopic example plant family Solanaceae
• Ground cherry (related to domestic potatoes)

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• Ground Cherry has post-pollination sepal growth
• Potatoes lack post-pollination sepal growth.
• In GC, sepals grow around a developing fruit
  (producing a Chinese lantern).
• MPF2 a transcription factor in Solanaceae
• Stimulates cell division, but
• 1. expressed in vegetative tissue in potatoes
• 2. expressed in vegetative AND floral tissue in
  ground cherries
• Involvement of MPF2
• Chinese lantern structure does not form if MPF2
  is knocked out experimentally.
• Therefore, MPF2 is responsible for lantern
  production.
• H1 a mutation resulted in MPF2 activity in
  floral tissue.

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A change in a regulator sequence produced a new
phenotype.
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Species Concepts

• Species Concept an idea about the kind of
  entity represented by the term SPECIES.
• Some concepts recognize the special reality of
  species (entities that exist independent of the
  investigator).
• Other concepts consider species to be classes of
  objects that exist because of the way that they
  are defined by an investigator.
• Species criteria standards for deciding whether
  or not a particular entity is a species.
• range of operationalism

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Species defined by a species concept Species
diagnosed by unique differences
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Species level lineages
Biparental organisms Organisms are united to form
species-level lineages by the process of
reproduction
Uniparental organisms Constant divergence because
lineages are not linked together by reproduction
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• The Biological Species Concept
• Ernst Mayr 1942, 1963. Animal Species and
  Evolution.
• Species are groups of actually or potentially
  interbreeding natural populations that are
  reproductively isolated from other such groups.
• Species ranking criterion absence of
  interbreeding
• Ancestral population may persist after
  speciation.
• Concept used to make decisions re the Endangered
  Species Act and many other important issues.
• Two obvious problems
• 1. Similar but divergent allopatric populations.
• 2. Asexuals and uniparental groups.

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• Morphological differences and similarities may
  not be effective in distinguishing species under
  this concept.
• 1. Individual variation (e.g., ontological
  variation)
• 2. Geographic variation
• 3. How much hybridization is permitted?
• 4. Cryptic species

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Ontological Variation
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Aspidoscelis tigris
2. Geographic variation
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3. How much hybridization is permitted?
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Red wolf
The red wolf problem
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A. tigris punctilinealis and A. tigris marmorata
OR A. tigris punctilinealis and A. marmorata?
3. One species or two?
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Arizona New Mexico
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(No Transcript)
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uniparens
velox
Aspidoscelis velox, 3n, parthenogenetic 1. A.
gularis stictogramma ?x A. inornata ? 2.
diploid parthenogen ? x A. inornata ?
4. Cryptic species
Aspidoscelis uniparens 3n, parthenogenetic 1.
A. inornata ? x A. gularis stictogramma ? 2.
diploid parthenogen ? x A. inornata ?
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• Barriers to interspecific hybridization
• Reproductive isolating mechanisms
• A. Prereproductive
• 1. Ecological
• Temporal (phenological)
• Habitat segregation
• 2. Behavioral
• 3. Mechanical
• 2. Postreproductive
• Gametic wastage