Phylogeny and Cladistics PDF

PHYLOGENY  PHYLOGENY Phylogeny is the study of relationships among different groups of organisms and their evolutionary development. Phylogeny attempts to trace the evolutionary history of all life on the planet. It is based on the phylogenetic hypothesis that all livin...

PHYLOGENY  PHYLOGENY Phylogeny is the study of relationships among different groups of organisms and their evolutionary development. Phylogeny attempts to trace the evolutionary history of all life on the planet. It is based on the phylogenetic hypothesis that all living organisms share a common ancestry.  PHYLOGENY A family tree for the evolutionary history of a species The root of the tree represents the ancestral lineage Tips of the branches represent descendants of the ancestor Movement upward shows forward motion through time Speciation: split in the lineage Shown as a branching of the tree CLADISTICS  CLADISTICS Cladistics refers to a biological classification system that involves the categorization of organisms based on shared traits. Organisms are typically grouped by how closely related they are and thus, cladistics can be used to trace ancestry back to shared common ancestors and the evolution of various characteristics.  CLADISTICS System of classification based on phylogeny Derived characteristics/traits: appear in recent parts of a lineage but not in older members PHENETICS vs. CLADISTICS IDENTIFYING SPECIFIC TRAITS OF ORGANISM CLADOGRAM & DICHOTOMOUS KEY  DICHOTOMOUS KEY A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of choices that lead the user to the correct name of a given item. "Dichotomous" means "divided into two parts". Therefore, dichotomous keys always give two choices in each step.  DICHOTOMOUS KEY Way of identifying organisms by looking at the physical characteristics Uses a series of questions to group into a hierarchy classification  CLADOGRAM A cladogram is a diagram used to represent a hypothetical relationship between groups of animals, called a phylogeny. A cladogram is used by a scientist studying phylogenetic systematics to visualize the groups of organisms being compared, how they are related, and their most common ancestors.  CLADOGRAM Cladograms are diagrams which depict the relationships between different groups of taxa called “clades”. By depicting these relationships, cladograms reconstruct the evolutionary history (phylogeny) of the taxa. Cladograms can also be called “phylogenies” or “trees”. Cladograms are constructed by grouping organisms together based on their shared derived characteristics. CLADOGRAM  CLADOGRAM A branching diagram to show the evolutionary history of a species Helps scientists understand how one lineage branched from another in the course of evolution  CLADOGRAM Example: 1. Given these characters and taxa CHARACTERS SHARK BULLFROG KANGAROO HUMAN VERTEBRAE X X X X TWO PAIRS OF X X X LIMBS MAMMARY X X GLANDS PLACENTA X  CLADOGRAM 2. Draw a Venn diagram. Start with the character that is shared by all the taxa on the outside. Inside each box, write the taxa that have only that set of characters. PLACENTA: HUMAN MAMMARY GLANDS: KANGAROO TWO PAIRS OF LIMBS: BULLFROG VERTEBRAE: SHARK  CLADOGRAM 3. Convert the Venn diagram into a cladogram like so: NEXT TOPIC: KINGDOMS