Topic 5

• Clade


  A group of organisms consisting of a common ancestor and all of its descendants
• Cladistics


  A method of classifying living organisms based on the construction and analysis of cladograms.
• Cladograms


  Tree diagrams that show the most probable sequence of divergence in clades.

  
• Nodes


  Each node corresponds to a hypothetical common ancestor that speciated to give rise to two (or more) daughter taxa
• Root


  The initial ancestor common to all organisms within the cladogram
• Outgroup


  The most distantly related species in the cladogram which functions as a point of comparison and reference group
• Analysis of cladograms


  - More nodes between two species, the less related they are expected to be.- The sequence of splits at nodes indicates when species diverged.
• Cladogram of some primates

  
• How to deduce if species evolved from a common ancestor


  (1) Base sequences of genes or amino acid sequences are used(2) Species with a recent common ancestor will have fewer differences(3) Species with an ancient common ancestor (10s of mya) have many
• Why is there a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor?


  since base sequences accumulate (gather together) gradually.
• Molecular clock


  The average rate that a species' genome mutates. This calculates when evolutionary divergence occurred from the common ancestor
• Homologous Structures


  Similar structures due to similar ancestry; Arise via divergent evolution; E.g. Pentadactyl Limb

  
• Analogous structures


  -> the opposite of homologous structures. Similar structures due to convergent evolution (similar functionality). E.g. Fins of shark and whale
• Morphology


  Deducing common ancestors using form and structure. This is inaccurate because it can be tough to distinguish homologous and analogous structures
• Why reclassification is important in cladistics


  This pushes classes closer to natural classification, revealing unnoticed similarities between groups. The predictive value is, therefore, higher.- A natural classification should be based on homologous characteristics.-Analogous characteristics can cause confusion and muddle the true classification.
• Reclassification


  the regrouping of species as more evidence becomes available as to their evolutionary origins.- Resulted from the analysis of DNA base and amino acid sequences allowed biochemical cladograms.
• Closest relatives to humans


  Chimpanzees and bonobos
• Figwort family


  Early massive family in cladistics organized by morphology. It had over 5 000 species
• What was found about the figwort family


  It was not a true clade; five clades had been initially combined into one family.
• Why cladograms are not always accurate


  They assume the smallest possible number of mutations occurred, which may be wrong. evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species.
• Divergent Evolution (adaptive radiation)


  the rapid evolutionary diversification of a single ancestral lineIt occurs when members of a single species occupy a variety of distinct niches with different environmental conditions
• Convergent evolution


  The independent evolution of similar features in species with distinct lineagesOccurs when different species occupy the same habitat and are subjected to the same environmental pressures (e.g. wings in birds and bats)
• Benefits of Taxonomy


  -Gives organisms globally recognised name-Can display relationships between organisms (allows evolutionary predictions)-easier to collect, sort, and group info
• Rules of Binomial nomenclature


  -First name is the genus name (group of species that share characteristics)-Second name is the species specific name-Genus name begins with capital and species name in lowercase-in italics-After referenced once, genus name can be shortened to first letter
• Hierarchy of Taxa


  -Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
• The 3 Domains


  - Eukaryota - Archaea - Eubacteria

  
• Natural Classification


  Grouping organisms based on morphological similarities
• Artificial Classification


  Arbitrarily selecting unifying characteristics first and then grouping organisms accordingly
• Disadvantage of Natural classification


  -Because they predict evolutionary relationships, they change with new information which means taxonomists sometimes reclassify groups of species
• Phyla of Invertebrate animals


  - Porifera- Cnidaria- Platyhelminthes- Annelida- Mollusca- Arthropoda- Chordata
• Porifera


  - Lack symmetry, no mouth, no anus, pores through body, cylindrical Eg. Sea Sponge
• Features of Cnidaria


  - Radial Symmetry (symmetry radiates from central point)- Aquatic- One mouth, no anus- Stinging cells- Tentacles- Eg. Jellyfish
• Platyhelminthes (Invertebrate animals)


  - Bilateral symmetry - Unsegmented- Flattened body shape- One mouth, no anus- Often parasitic- Eg. Tapeworm
• Arthropods (Invertebrate animals)


  - bilateral symmetry- Exoskeleton- Segmented bodies- Heart on dorsal side of body- Eg. Shrimp, spider, insects
• Amphibians (Vertebrate animals)


  -moist skin permeable to water and gases-simple lungs-four legs when adult-external fertilisation-larval stage in water, adult on land-do not maintain constant body temperature
• Reptile


  -Impermeable skin-Lungs-Four legs in most species-Internal fertilisation-four legs in most species-do not maintain constant body temperature
• Bird


  -skin with feathers-Lungs-limbs-two legs, two limbs-internal fertilisation-beak, no teeth-maintain constant body temperature
• Mammal


  -skin with hair, lungs four legs, or two legs, and two arms, internal fertilisation ,Maintain constant body temperature
• Annelida (Invertebrate animals)


  - Bilateral symmetry- seperate mouth and anus- bristles often present- Segmented body- Eg. Earthworm, leeches
• Mollusca (Invertebrate animals)


  - Soft bodies- Vascular foot-seperate mouth and anus- Shell may be present-no segmentation- Eg. Snail and slugs