week 18

• Molecular and Human Evolution
• Aims


  • Principles of molecular evolution
  • Application of molecular biology to evolutionary studies
  • Human evolution – classical and molecular studies
• Some major stages in the evolution of life
• Molecular Evolution


  • Problems with gaps in the fossil record
  • Especially soft bodied organisms and micro-organisms
  • Use DNA and protein sequences to study evolution
• • Changes in DNA sequence
  • Changes in protein sequence
  • Evolution of gene families
• How do genomes evolve?

  1. Changes occur in the DNA sequence

  2. Mutations

  3. Recombination

  4. Changes must become FIXED in the population to be involved in evolution
• Stages of genome evolution

  • Individual with a mutation/change
  • Population
  • Mutation is lost
  • Mutation is FIXED in the population
• • How do genomes evolve?
  • Changes occur in the DNA sequence
  • Especially soft bodied organisms and micro-organisms
  • Some DNA changes affect the protein sequence
  • Changes in the protein sequence can change the function of the protein
  • More complex evolutionary consequences
• Types of mutations


  • Simple base changes (GATC to GA, G, C)
  • Insertions (GATC to GAT, GGG, C)
  • Deletions (GA to T, C, GAC)
  • Chromosome rearrangments
• Using DNA to understand evolution

  1. Evolutionary time

  2. Living (extant) species

  3. Phylogenetic tree
• Phylogenetic tree


  • Homologous genes (identical function)
  • Aligned DNA sequences for comparison
  • Comparison of similarities between DNA sequences
• How do we construct a phylogenetic tree?

  1. Choose appropriate DNA sequences

  2. Align the DNA sequences

  3. Compare similarities between the DNA sequences

  4. Build the phylogenetic tree
• Example of comparing 4 species DNA sequences and calculating % similarity
• Building a similarity matrix
• Constructing a phylogenetic tree from the similarity matrix
• Rooted vs unrooted phylogenetic trees
• Examples


  • Mitochondrial DNA
  • Ribosomal RNA genes
• Mitochondrial DNA


  • Does not undergo recombination
  • Passed down the maternal line
  • Simplifies evolutionary interpretations
  • Good for identifying human evolution
• Ribosomal RNA genes


  • Key component of ribosomes
  • Ribosomes make proteins
  • Present in all life
  • Highly conserved in evolutionary terms
  • Good for evolutionary studies across the whole of life
• Ribosomal components


  • mRNA
  • Ribosome
  • Large subunit
  • Small subunit
  • Ribosomal RNA
  • rRNA genes (DNA)
  • Tandemly repeated genes
  • Highly conserved across species
  • Highly variable across species
  • (non-transcribed spacer)
• Ribosomal RNA genes


  Genes that encode ribosomal RNA, a key component of ribosomes
• mRNA


  Messenger RNA, which carries the genetic instructions from the nucleus to the ribosome
• Components of the ribosome

  • Large subunit
  • Small subunit
  • Ribosomal RNA
• rRNA genes (DNA)


  The DNA sequences that encode ribosomal RNA
• Ribosomal RNA genes


  • Tandemly repeated genes
  • Highly conserved across species
  • Highly variable across species
  • (non-transcribed spacer)
• Gene families


  Families of related genes that produce proteins with related but different functions
• Gene family example


  • Haemoglobin genes (α1, α2, β, δ)
• Haemoglobin genes have a critical function of carrying oxygen around the body
• Haemoglobin genes


  • α1
  • α2
  • β
  • δ
  • γ
  • ζ
  • ε
• Pseudogenes


  Genes that have lost their function
• Pseudogenes are referred to with the Greek letter psi (Ψ)
• Characteristics of humans


  • Bipedal
  • Tooth conformation
  • Increased brain size
  • Cultural behaviour
  • Language
• Hominins


  Humans and our close extinct relatives
• Hominids


  The family that includes orangutans, gorillas, chimpanzees and humans
• Taxonomic groups


  • Family: Hominidae
  • Subfamily: Homininae
  • Tribe: Hominini
• Sahelanthropus tchadensis fossils found in Chad, Africa

  1. 7 million years ago
• Australopithecus afarensis ("Lucy") fossils found

  1. 3 million years ago
• Homo habilis fossils found alongside tools

  2.5 million years ago
• Brain volume


  Increases relative to body weight in hominins
• Homo erectus fossils found outside Africa


  1.8 million years ago