Chapter 5 Evol Bio PDF

Variation  Among   Individuals     Variation  among  individuals  is   the  raw  material  for  evolution     Thamnophis   Asteraceae   Human  Popula1on   Three  Kinds  of   Variation     three  different  kinds  of   variation  amo...

Variation  Among   Individuals     Variation  among  individuals  is   the  raw  material  for  evolution     Thamnophis   Asteraceae   Human  Popula1on   Three  Kinds  of   Variation     three  different  kinds  of   variation  among  individuals   These  are  gene1c  varia1on,  environmental  varia1on,  and   genotype-­‐by-­‐environment  interac1on.     The  Machinery  of  Life:  Proteins     Different  kinds  of  cells  are  dis1nguished  by  the  proteins  they   make   The  Machinery  of  Life:  Genetic   Material     Organisms  carry  instruc1ons  for  how  to  build  the  proteins   they  use,  as  well  as  for  when,  where,  and  in  what  quan11es  to   make  them,  in  their  gene1c  material.     The  gene1c  material  is  RNA  in  some  viruses.  In  other  viruses,   and  all  cellular  forms  of  life,  the  gene1c  material  is  DNA.     The  Machinery  of  Life:  Genetic   Material     Genes  in  organisms  are  embedded  in  long  DNA  molecules   called  chromosomes.  A  typical  chromosome  carries  numerous   genes.  The  physical  loca1on  of  a  gene  on  a  chromosome  is   called  the  gene’s  locus.     Some  of  the  genes  on  human  chromosome  7   The  Machinery  of  Life:  Genetic   Material     The  Machinery  of  Life:  From   Genes  to  Proteins   What  is  the  the  mechanisms  responsible   variations  among  individual       Gene1c  varia1on  is  the  result  of  differences   among  individuals  that  are  encoded  in  their   DNA.     Environmental  varia1on  arises  when  external   factors  influence  how  much  protein  is  made   from  par1cular  genes,  or  how  the  proteins   work.     Genotype-­‐by-­‐environment  interac1on  is  the   result  of  differences  among  individuals  that   are  encoded  into  their  DNA  and  that  make   them  differ  in  their  sensi1vity  to   environmental  influences.     Genetic  Variation       Albinism  among  the  Hopi  Na1ve  Americans.  In  this  photograph,  taken  about   1900,  the  Hopi  girl  in  the  center  has  albinism.   variation  in  the  perception  of   taste:  PTC     Taste  receptor  proteins  have  diverse  shapes  and  chemical  proper1es.   Each  kind  of  taste  receptor  protein  binds  with  a  subset  of  the  chemicals   in  food,  corresponding  to  sweet,  sour,  salty,  umami  (savory),  and  biSer   flavors     variation  in  the  perception  of   taste:  PTC     One  way  to  demonstrate  this  varia1on  is  to  offer  people  small   quan11es  of  the  chemical  phenylthiocarbamide  (PTC)     variation  in  the  perception  of   taste:  PTC   The  one  that  binds  PTC  is  TAS2R38,   encoded  by  a  gene  on   chromosome  7     The  most  common  TAS2R38   alleles,  named  for  the  amino  acids   they  specify  at  the  variable  sites,   are  AVI  and  PAV.   Considering  just  alleles  AVI  and   PAV,  the  three  possible  genotypes   are  AVI/AVI,  AVI/PAV,  and  PAV/ PAV     variation  in  the  perception  of   taste:  PTC   The  human  life  cycle  (a)  We  spend  most  of  our  lives  in  a  diploid  phase,  carrying  a  complete  set  of   chromosomes  received  via  the  egg  and  a  complete  set  received  via  the  sperm.  Each  gamete  we   make  receives  one  member  of  each  chromosome  pair.  (b)  We  can  thus  use  a  PunneS  square  to   calculate  the  odds  that  a  zygote  will  have  a  par1cular  genotype     Genetic  Variation  and   Evolution     We   have   looked   at   gene1c   varia1on   among   HIV   virions   in   their   suscep1bility   to   the   an1retroviral   drug   AZT   as   well   as   gene1c   varia1on  among  humans  in  the  suscep1bility  to  HIV  infec1on.     We   have   considered   gene1c   varia1on   among   s1cklebacks   in   the   extent  of  body  armor  and  gene1c  varia1on  in  fruit  size  in  tomatoes.     Environmental   Variation     Water  Flea  vs  Phantom  Midges   Our  example  of  environmental   varia1on  concerns  a  prey  species,   the  water  flea,  and  its  predator,  a   larval  insect.     Water  fleas  are  1ny  freshwater   crustaceans  that  inhabit  lakes  and   ponds  all  over  the  world  (Lampert   2011).   Among  the  traits  that  make  water  fleas  useful  for  the  study  of  environmental   varia1on  is  that  when  condi1ons  are  auspicious  they  reproduce  by  cloning,   switching  to  sexual  reproduc1on  only  when  condi1ons  deteriorate.  Also   useful  is  that  certain  environmental  cues  trigger  changes  in  their  morphology,   physiology,  and  behavior.     Water  Flea  vs  Phantom  Midges   Daphnia  pulex  is  capable  of  developing  a  morphology  that  is   well  defended  against  phantom  midges.    It  can  nearly  double   the  strength  and  thickness  of  its  carapace  and  grow  ridges,   called  neckteeth,  on  the  back  of  its  head     Environmental  Variation  and   Evolution   A  bacterium  making  equal  amounts  of  both  versions  of  GFP  would  be  yellow,  a   cell  making  more  of  one  version  would  be  green,  and  a  cell  making  more  of  the   other  version  would  be  orange.  The  explana1on  for  the  diversity  of  colors  in  the   photo  is  random  varia1on  in  the  interac1ons  between  the  promoters  and  the   regulatory  proteins  that  ac1vate  and  deac1vate  them.     Genotype-­‐by-­‐ Environment   Interaction   Genotype  and  temperature   inGluence  sex  in  leopard  geckos     (a)  A  leopard  gecko  (Eublepharis  macularius).  (b)  Individuals  incubated   at  intermediate  tempera-­‐  ture  are  more  likely  to  be  male.     Development  along  the  female  versus  the  male   pathway  involves  changes  in  the  production  of  a   variety  of  proteins     Expression  of  the   gene  Sox9  in  the   gonad  ceases   earlier  in  leopard   geckos  developing   as  females  than  as   males   Sox9  encodes  a   transcrip1on  factor   that  directs  the   expression  of  other   genes  and  thus   commits  the  gonad   to  being  a  tes1s   versus  an  ovary.     Genotype-­‐by-­‐Environment  Interaction:   Serotonin  Transporter  Gene   Genotype-­‐by-­‐Environment  Interaction:   Serotonin  Transporter  Gene   Among  people  with   genotype  ll  for  the   serotonin  transporter   gene,  maltreatment  in   childhood  has  liSle  effect   on  the  probability  of   major  depression  in  early   adulthood,  whereas   among  people  with   genotype  ss   maltreatment  increases   the  probability  of   depression  substan1ally     Genotype-­‐by-­‐Environment  Interaction:   Phenotypic  Plasticity   An  organism  that  develops  different  phenotypes  in  different   environments  is  said  to  exhibit  phenotypic  plas1city.     When  popula1ons  harbor  gene1c  varia1on  for  environmental   sensi1vity,  popula1ons  can  evolve  greater  or  lesser  plas1city.     Insect  genotype-­‐  by-­‐environment  interac1on   (a)  A  normal  tobacco  horn-­‐  worm.  (b)  A  black  mutant.  (c)  Some   black  mutants  turn  green  a_er  heat  shock.     Where  New  Alleles   Come  From     The  structure  of  the  genetic   material     Mutation  due  to  DNA  Alteration:  Spontaneous   Deamination   Mutation  due  to  DNA  Alteration:   Premutations   DNA  altera1ons  s1ll   suscep1ble  to  repair,   are  known  as   premuta1ons     How  Mutations  Alter  Protein   Function     cell  makes  a  protein  from  the  instruc1ons  encoded  in  a  gene,   it  follows  a  two-­‐step  process:  TRANCRIPTION  &  TRANSLATION   How  Mutations  Alter  Protein   Function     synonymous  (or  silent)   subs1tu1on  -­‐  a   muta1on  leaves  the   encoded  protein   unaltered     nonsynonymous  (or   replacement)   subs1tu1on  -­‐  muta1on   that  changes  the   amino  specified  by  a   codon     How  Mutations  Alter  Protein   Function     synonymous  (or   silent)   subs1tu1on  -­‐  a   muta1on  leaves   the  encoded   protein  unaltered     nonsynonymous   (or  replacement)   subs1tu1on  -­‐   muta1on  that   changes  the   amino  specified   by  a  codon     How  Mutations  Alter  Protein   Function     Where  New  Genes   Come  From     Two  mechanisms  of  gene   duplication     A  New  Gene  Generated  by   Unequal  Crossing  Over     Phylogeny  of  RNASE1  genes.   RNASE1  reac1on  norms.   Paralogous  vs  Orthologous   A  New  Gene  Generated  by   Retroposition     chondrodysplasia,  the  short-­‐legged  condi1on  characteris1c  of   corgis,  dachshunds,  bassets,  and  a  variety  of  other  breeds   on  chromosome  18,  a  duplicate  copy  of  the  gene  for  fibroblast   growth  factor  4  (fgf4)  is  found.  Possession  of  the  duplicate  is   strongly  associated  with  chondrodysplasia       A  New  Gene  Generated  by   Retroposition     hhsh   New  Genes  from  Scratch     C22orf45  is  a  gene  of  unknown  func1on  unique  to  humans.  It   is  transcribed  in  a  variety  of  1ssues,  and  its  mRNA  is  known  to   be  translated  into  protein.     A  new  human  gene  from  noncoding  DNA.  In  other  apes  and  in  macaques,  the   sequence  homologous  to  the  human  gene  C22orf45  contains  a  premature   stop  codon   Chromosome   Mutations     Inversions     Chromosome   inversions   o_en   result  from  a  mul1step  process   that   starts   when   radia1on   causes   two   double-­‐strand   breaks  in  a  chromosome.  A_er   breakage,   a   chromosome   segment   can   detach,   flip,   and   r e a n n e a l   i n   i t s   o r i g i n a l   loca1on.     W h e n   i n v e r s i o n s   a r e   heterozygous,   the   inverted   s e q u e n c e s   c a n n o t   a l i g n   properly   when   homologs   synapse   during   prophase   of   meiosis  I.     Inversions  in  Drosophila   Drosophila  subobscura  is  a  fruit  fly  na1ve  to  western  Europe,   North  Africa,  and  the  Middle  East,  and  has  six  chromosomes.     Five  of  these  chromosomes  are  polymorphic  for  at  least  one   inversion.   Biologists  have  known  since  the  1960s  that  the  frequencies  of   these  inversions  vary  regularly  with  la1tude  and  climate.     This  type  of  regular  change  in  the  frequency  of  an  allele  or  an   inversion  over  a  geographic  area  is  called  a  cline.     But  is  the  cline  really  the  result  of  natural  selec1on  on  the   supergenes?  Or  could  it  be  a  historical  accident,  caused  by   differences  in  the  founding  popula1ons  long  ago?     Inversions  in  Drosophila   From  Old  world  to   New  world   Of  the  80  inversions   present  in  Old  World   popula1ons,  precisely   the  same  subset  of  19   is  found  in  both  Chile   and  Washington  State.     This  is  strong  evidence   that  the  clines  result   from  natural  selec1on   and  are  not  due  to   historical  accident.     Inversions  in  Drosophila   Which  genes  are  locked  in   Research  by  George   the  inversions,  and  how  do   Gilchrist  and  colleagues   they  affect  adapta1on  to   (2004)  has  confirmed  that   changes  in  climate?     pronounced  and  parallel   clines  in  body  size  exist  in   fly  popula1ons  from  North   America,  South  America,   and  Europe.     alleles  in  the  inversions   affect  body  size,  and  that   natural  selec1on  favors   large  flies  in  cold,  wet   climates  and  small  flies  in   hot,  dry  areas.     Genome   Duplication     if  homologous  chromosomes  fail   to  segregate  during  meiosis  I  or  if   sister  chroma1ds  do  not  separate   properly  during  meiosis  II,  the   resul1ng  cells  may  have  double   the  number  of  chromosomes  of   the  parent  cell.     Organisms  with  more  than  two   chromosome  sets  are  said  to  be   polyploid     There  are  at  least  two  reasons  that  polyploidy   is  an  important  type  of  mutation  in  evolution   First,  it  can  lead  to  new  species  being   formed.     Second,  it  alters  cell  size,  cell   geometry,  and  gene  dosage,  and  thus   may  endow  individuals  with  new   phenotypes  that  allow  them  to   colonize  and  adapt  to  new   environments.     Most  allopolyploids  arise  from  hybridization   between  two  species  followed  by  chromosome   doubling.     Polyploidy  and  Speciation     Genome  Duplication  and   Adaptation:  Achillea  borealis     Jus1n  Ramsey  (2011)  tested  the  hypothesis  that  polyploidy   facilitates  the  coloniza1on  of,  and  adapta1on  to,  new   environments  by  performing  a  common  garden  experiment   with  wild  yarrow     Tetraploid  popula1ons  live  in   coastal  grasslands,  conifer   forests,  and  mountain  meadows.     Hexaploid  plants  live  in  sand   dunes  and  oak  woodlands.   Genome  Duplication  and   Adaptation:  Achillea  borealis     Ramsey  grew  tetraploid  plants,  first-­‐genera1on  hexaploid   plants  from  tet-­‐  raploid  parents  (neo-­‐hexaploids),  and   hexaploid  plants—all  from  wild  popula-­‐  1ons—next  to  each   other  in  sand  dunes.  He  monitored  them  for  three  years.     Survival  of  plants  with  different  ploidy   in  a  common  garden  in  dunes.   Flowering  1me  distribu1ons  in   the  same  plants.