Natural and Artificial Selection Notes PDF

  NATURAL  AND  ARTIFICIAL  SELECTION     natural  selection  =  the  process  by  which  characteristics  of  a  population  change  over  many   generations  as  organisms  with  heritable  traits  survive  and  reproduce,  passing  their...

  NATURAL  AND  ARTIFICIAL  SELECTION     natural  selection  =  the  process  by  which  characteristics  of  a  population  change  over  many   generations  as  organisms  with  heritable  traits  survive  and  reproduce,  passing  their  traits  to  offspring.         B   D   F   A   C   E   G         I   J   L   H   K   M     N     O         Organisms  are  selected  for  b y  their  environmental     conditions.       NATURAL  SELECTION         Those  individuals  without     Those  individuals  with   characteristics  that  allow  them  to     characteristics  (alleles)  that  increase   survive  their  environment  will  die!     their  chance  of  survival  will  live.       C     A   F     D     B   E   G     L     O   H   M   I   K       J   N     These  individuals  can     reproduce  and  pass  their     alleles  on  to  offspring.   ALL  DIE!             The  entire  population  will  possess  the  allele     that  increased  their  chance  of  survival.     An  abiotic  (non-­‐living)  environmental  condition  can  select  FOR  certain  characteristics  in  some   individuals  and  select  AGAINST  different  characteristics  in  other  individuals.  The  environment   exerts  selective  pressure  on  a  population.  Biotic  factors  (predators,  parasites,  competition  between   organisms)  can  also  exert  selective  pressure  on  a  population.       NATURAL  SELECTION     cannot  predict  environmental  change   has  no  purpose,  no  will,  no  specific  direction   it  is  situational  –  a  trait  may  be  unimportant/irrelevant  in  one  situation  but  very  beneficial   in  another!   a  beneficial  trait  increases  the  chances  of  survival  and  increases  the  chance  of  reproducing   and  there  will  be  an  increase  in  the  number  of  individuals  in  the  population  with  that  allele   for  the  trait  –  the  population  will  be  better  adapted  to  their  environment!     What  is  fitness?    Fitness  is  the  contribution  an  individual  makes  to  the  gene  pool  of  the  next   generation  by  producing  offspring  that  survive  long  enough  to  reproduce.  If  an  organisms  has  a  high   degree  of  fitness,  it  will  survive,  reproduce  and  pass  its  advantageous  genes  to  its  offspring  and   they  will  survive  long  enough  to  reproduce!    Also,  if  an  organism  has  many  viable  offspring,  it  has  a   high  degree  of  fitness.     LAB:  Modelling  Natural  Selection  from  McGraw  Hill,  Page  306     ARTIFICIAL  SELECTION     artificial  selection  =  selective  pressure  exerted  by  humans  on  populations  in  order  to  improve  or   modify  particular  desirable  traits   artificial  selection  occurs  with   o farm  animals  –  cows  are  bred  to  increase  milk  production,  chickens  are  bred  to  grow   fast  and  have  more  muscle   o pets  –  dogs  and  cats  are  bred  for  appearance   o food  crops  are  bred  to  increase  yield  and  nutritional  value,  be  drought-­‐  and  pest-­‐ resistant   selective  breeding  is  a  form  of  artificial  selection   crop  breeders  know  how  to  balance  selective  breeding  with  maintaining  genetic  variation     VIDEO  –  Corn     There  are  consequences  to  artificial  selection.   as  we  select  and  breed  for  certain  characteristics,  we  decrease  genetic  diversity   as  we  select  for  a  desirable  trait  some  negative  traits  are  also  ‘selected’  unknowingly  –  for   example,  the  bulldog  is  selected  for  its  flat  face  yet  it  has  respiratory  problems     monoculture  =  extensive  plantings  of  the  same  varieties  of  a  species  over  large  expanses  of  land  (ex.   100,000’s  of  km2  of  wheat)   Advantage  of  monoculture  –  easier  to  manage  a  single  type  of  plant  (one  herbicide,  one   insecticide,  one  fertilizer)   Disadvantage  of  monoculture  –  decrease  in  genetic  diversity.  As  a  result,  if  a  new  stress  is   introduced  to  the  population  of  plants  (new  disease,  new  pest,  climate  change)  the  whole   crop  can  be  devastated  because  it  doesn’t  have  the  diversity  needed  to  deal  with  these   changes.   Companies  have  created  gene  banks  that  have  populations  of  early  ancestors  of  modern  plants.  As  a   result,  their  genetic  diversity  is  available  to  re-­‐introduce  into  modern  plants  if  needed!    Our  most   important  crop  plants  came  from  wild  ancestors  with  genetic  information  that  gave  them  the  ability   to  survive  and  reproduce.     VARIATION  WITHIN  A  SPECIES  LEADS  TO  CHANGES  IN  A  POPULATION  OVER  GENERATIONS  AND   ALLOWS  POPULATIONS  TO  ADAPT  TO  EVER0CHANGING  ENVIRONMENTS.