gen bio Q4W7

• Evidence of evolution


  • Structural
  • Genetic
  • Biogeographical
• Homologous structures


  Traits that are shared due to common ancestry
• Homologous structures


  • Forelimbs of whales, humans, and birds
• Vestigial structures


  Structures that serve little or no present purpose for an organism
• Analogous structures


  Structures that evolved independently in different organisms because the organisms lived in similar environments or experienced similar selective pressure
• All living organisms share the same genetic material (DNA), similar genetic codes, and the same basic process of gene expression (transcription and translation)
• Homologous genes


  Genes that are "the same" because they were inherited from a common ancestor
• The more DNA differences in homologous genes between two species, the more distantly the species are related
• Gel electrophoresis


  A technique used to analyze segments of DNA by separating them by size
• Bands that are similar in size between samples on a DNA gel indicate that DNA sequence is shared, and the more fragments two samples share, the more related they are to one another
• Biogeography


  The study of the distribution of organisms, both past and present
• Broad groupings of organisms that had already evolved before the breakup of the supercontinent Pangaea tend to be distributed worldwide, while broad groupings that evolved after the breakup tend to appear uniquely in smaller regions of Earth
• Rooted phylogenetic tree


  A tree that attempts to identify when various species diverged from a common ancestor
• Unrooted phylogenetic tree


  A tree that shows relationships among species but does not show a common ancestor
• Branch point


  The point where a single lineage evolved into a distinct new one
• Basal taxon


  A lineage that evolved early from the root and remains unbranched
• Sister taxa


  Two lineages that stem from the same branch point
• Polytomy


  A branch with more than two lineages, indicating where scientists have not definitively determined all of the relationships
• Sister taxa


  A branch with two lineages
• Polytomy


  A branch with more than two lineages, illustrating where scientists have not definitively determined all of the relationships
• Sister taxa and polytomy share an ancestor, but it does not mean that the groups of organisms split or evolved from each other
• Root of a phylogenetic tree


  Indicates that an ancestral lineage gave rise to all organisms on the tree
• Branch point


  Where two lineages diverged
• Basal taxon


  A lineage that evolved early and remains unbranched
• Sister taxa


  When two lineages stem from the same branch point
• Polytomy


  A branch with more than two lineages
• Many disciplines within the study of biology contribute to understanding how past and present life evolved over time
• Systematics


  The scientific field that organizes and classifies organisms based on evolutionary relationships
• Data used to build phylogenetic trees

  • Fossils
  • Studying the structure of body parts or molecules
  • DNA analysis
• Phylogenetic trees are hypotheses that will continue to change as new types of life are discovered and new information is learned
• Types of evidence used in phylogenetic investigations

  • Morphologic (form and function)
  • Genetic
• Integrating anatomy and genetics aids in determining the evolutionary relationship between different organisms
• Phylogenetic tree


  A tree-like diagram that shows the evolutionary relationships among various biological species or other entities based on similarities and differences in their physical or genetic characteristics
• The more information you can compare, the more accurate the phylogenetic tree will be
• Any DNA, RNA, or protein sequence can be used to generate a phylogenetic tree, but DNA sequences are most commonly used
• Descent with modification


  1. Organisms evolve from common ancestors and then diversify

  2. A change in the genetic makeup of an organism leads to a new trait which becomes prevalent in the group

  3. Many organisms descend from this point and have this trait

  4. New variations continue to arise: some are adaptive and persist, leading to new traits

  5. With new traits, a new branch point is determined
• Distantly related organisms can share morphological features, but morphology is not particularly useful for determining evolutionary relationships among some groups of organisms
• Genetic data have shown that very closely related Cyanobacteria can have very different cell shapes, and Cyanobacteria with similar shapes may be only distantly related to each other
• Genes


  The units of organisms that encode the results of evolution, making them particularly useful for building phylogenetic trees
• Different genes evolve in different ways, genes can be swapped among organisms, and genes can be lost by organisms, so the choice of genes to use for a phylogenetic tree needs to reflect the scientific questions being asked