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Final

BIO153 Exam Notes- All Covered Chapters.pdf

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Department
Biology
Course
BIO153H5
Professor
Christoph Richter
Semester
Winter

Description
  Cambrian  Fossils:  An  Overview   • The  Cambrian  explosion  is  documented  by  three  major  fossil  assemblages  (Figure  27.12a).   • The  presence  of  these  exceptionally  rich  deposit s  before,  during,  and  after  the  Cambrian  explosion  makes   the  fossil  record  for  this  event  extraordinarily  complete.     The  Doushantuo  Microfossils   • Researchers  identified  sponges,  cyanobacteria,  and  multicellular  algae  in  samples  dated  570 –580  Mya.   They  also  found  what  they  concluded  were  animal  embryos  in  early  stages.     The  Edicaran  Faunas   • Sponges,  jellyfish,  comb  jellies,  and  traces  of  other  animals  dated  544 –565  Mya  are  found  in  fossils  from   the  Ediacara  Hills  of  Australia.     The  Burgess  Shale  Faunas   • Virtually  every  major  animal  group  is  represented  in  the  Burgess  Shale  fossils,  which  date  525 –515  Mya.   • These   fossils   indicated   a   tremendous   increase   in   the   size   and   morphological   complexity   of   animals,   accompanied  by  diversification  in  how  they  made  a  living.     Did  Gene  Duplication  Trigger  the  Cambrian  Explosion?   • Many   researchers   predicted   there   would   be   a   strong   association   between   the   order   in   which   animal   lineages  appeared  during  evolutionary  history,  the  number  of  Hox  genes  present  in  each  lineage,  and  each   lineage's  morphological  complexity  and  body  size.   • A  phylogenetic  tree  of  Hox  genes  in  animals  in  general  support  this  hypothesis  (Figure  27.13).   • The  following  conclusions  can  be  made  from  this  phylogeny:   –the  number  of  genes  in  the  Hox  cluster  appears  to  hav e  expanded  during  the  course  of  evolution   –Hox  genes  appear  to  have  been  created  by  gene  duplication  events  because  the  genes  within  the  cluster   are  similar  in  structure  and  base  sequence   –the  entire  Hox  cluster  was  duplicated  and  then  duplicated  again  in   the  lineage  leading  to  vertebrates   • Duplication  of  Hox  genes  has  been  important  in  making  the  elaboration  of  animal  body  plans  possible.   • However,  changes  in  expression  and  function  of  existing  genes  have  been  equally  or  even  more  important.                                              
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