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Lecture 11

BIOLOGY 1M03 Lecture 11: 11- Phylogenies, Parsimonies, Convergence

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Ben Evans

Bio 1M03 January 28, 2016 Maximum Parsimony, Homology and Homoplasy, Convergence and Adaptive Radiation Phylogenies - The cladistics or maximum parsimony approach to inferring a phylogeny focuses on synapomorphies - Synapomorphies a shared derived characteristic - A synapomorphy is a novel trait that a clade of organisms have and that others outside this clade lack - A novel trait that is in an ancestor that has t ha trait and all derived organisms contain that trait - Also happen in molecular data - Occurs in nucleotides - Mutation occurs changing the nucleotide sequence - Synapomorphy must be shared between all descendants and must be unique to the clade - More complex explanations less parsimonious - The observed data can be explained through phylogenies and the one with the smallest mutations or change is selected as it is easier to explain and is more parsimonious - Synapomorphies identify monophyletic groups - The more parsimonious approach is the more simplistic and easier to understand or justify - Monotremes do not have nipples, lactate through sweat glands - Placentals and Marsupials have nipples Homology - Homology: similarities are inherited from a common ancestor - Hox genes are conserved (genes that govern body form and what part of the embryo develops into what) - Appear in the same order in the chromosome - Appear in multiple animals - Suggests that these animals have a common ancestor and ti was inherited form the common ancestor - Synapomorphic trait - Hox genes are expressed in the embryo in the same place as it is expressed in adult form - This is true in all organism that contain hox genes - Hox genes did not develop independently - Similar DNA sequences in humans fruit flies etc - Similar genomic organization - Appears in the same order within species - Similar function - Define where the body parts are - Other species related t fruit flies and humans have these features - Similar expression patterns during development - Similarity is observed between species Hompolasy - Homoplasy: occurs when traits are similar for reasons other than common ancestry - Convergent evolution - Similar traits can evolve independently in two distant species - Shared traits but are independently evolved - Not due to shared ancestry - Convergent evolution creates homoplasy - Bones are homologous but wings are homoplasious - Occurs in molecular data more than in morphological data - Example: dolphins and ichthyosaur both have streamlined bodies, long jaws and fins and flippers but their ancestors did not Distinguishing Homology from Homoplasy - Convergent evolution: occurs when natural selection favors similar solutions to the problems posed by a similar way of life - Shown in the dolphin and ichthyosaur example - Convergent evolution is a common cause of homoplasy - Another example is the evolution of wings - Convergence of DNA can occur too - Phylogeny of vertebrae animals, showing convergence of swimming on the fish body shape - Maximum parsimony assumes that the best explanation or patter is the one that implies the least - Convergent evolution and other causes of homoplasy should be rare compared with similarity due to shared ancestry, so the tree that implies the fewest overall evolutionary changes should be the one that most accurately reflects what happened during evolution Whales Study - Traditionally, cladograms based on morphological data place whales outside of the artiodactyls - Artiodactyls are mammals that have hooves, and even number of toes and an unusually pulley shaped ankle bone - The original derivation that scientists concluded were incorrect - Whales and hippos contained events that other artiodactyls (the clade) lacked - Recent data on gene sequences called short interspersed nuclear elements (SINEs) show that whales and hippos share several SINE genes that are absent in other artiodactyl groups - These SINEs are shared derived traits (synapomorphies) and support the hypothesis that whales and hippos are indeed closely related. - Whales and hippos shared
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