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Lecture 14

HMB200 2014 Lecture 14.pdf
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Department
Human Biology
Course
HMB200H1
Professor
John Yeomans
Semester
Winter

Description
  Lecture  14:  Sex  and  Gender     Sex  and  gender   • Critical  thing  that  distinguishes  male  and  female  has  nothing  t o  do  with  gonads,  behavior,  or  appearance   • Appearance  of  the  gametes  are  more  important   • In  humans,  there  is  a  tremendous  difference  in  size  between  the  gametes   • Can  determine  if  its  male  or  female  b y  looking  at  any  ell  in  the  body   –  for  x  or  y   • There  are  7-­‐8  different  ways  we  can  define  what  sex  and  gender  are,  like  appearance.  However,  appearance   doesn't  apply  to  all  animals!   • Biological  definition:  Large  gametes  (ovum)  =  females;  small  gametes  =  male   • Related  to  the  biological  definition,  Chromosomes:  found  in  all  cells  of  our  body.  The  Y  chromosomes  is  what   determines  the  differentiation  in  the  genitalia  (I.e.  identifies  the  male)   o Exceptions:  XO  (female),  XXY  (male)  and  XYY  (male)   ß  note  that  it  is  the  Y  that  is  the  determining  factor   o Chromosomes  can  be  used  to  differentiate  gender  right  after  birth  while  gamete  production  cannot  be   determined  until  after  puberty     • Genitalia  are  similar  in  appearance  in   both  males  and  females  6  week  of   gestation   • By  15  weeks,  differentiation  of  external   genitalia  and  internal  gonads   • Genitalia  of  male  and  female  are  similar   in  appearance  until  several  weeks  later   that  you  see  differentiation  of  external   genitalia,  and  internal  gonads   • Presence  of  sex  hormones  (Esp.   androgens)  that  cause  differentiation  of   male     Sexual  differentiation   •   • How  is  differentiation  achieved?   • SRY  gene  -­‐  Sex  determining  Region  of  the  Y  chromosome  à  the  cause  of  differentiation   • Single  gene  results  in  the  production  of  testosterone  in  the  male  gonad   à  causes  male  gonad  to  go  from  an   undifferentiated  state  (same  as  female)  to  be  altered  by  the  presence  of  testosterone  when  SRY  gene  is   expressed   o Male  gonad  produces  2  hormones:  testosterone  (produces  most  of  the  changes)  and   the  anti-­‐mammarian   hormone  (reduction  of  mammarian  ducts)  à  these  2  hormones  result  from  the  expression  of  the  SRY  gene   on  that  one  chromosome   • Needs  gene  to  cause  differentiation   • Undifferentiated  states:  female   • Differentiate  sry:  male   • Occur:  male   • Don’t  occur:  primary  sex  characteristics  remain  female   • Single  gene  that  results  in  production  of  testosterone  in  male  gonads   • Causes  male  gonads  to  change  form  undiffe rentiated  state  –  when  sry  gene  is  expressed,  testosterone  alters   structure  of  gonad   • Single  gene  expression  produces   testosterone  in  the  male  gonad  to  change  and  antimullerian  hormone  (AMH)  to   reduce  the  mullerian  duct  found  in  females  (shrinks  it)   • Undifferentiating  becomes  females       • Testosterone  acts  on  estrogen  receptors  in  the  brain     • MALES:  Testosterone  in  the  brain   converts  into  estrogen  via   • Testosterone  goes  to  the  brain:     aromatase.  This  testosterone  converted  estrogen  then  acts  on   estrogen  receptors  that  lead  to  brain  changes  which  cause  secondary   sex  characteristics     • In  FEMALES:  Estrogen  is  bound  by  alpha  feto -­‐protein  (αFP)  in  the   periphery  to  prevent  bin ding  of  estrogen  receptors  (do  not  get  to   brain)   • These  changes  are  most  visible  in  the  preopric  area  of  the   hypothalamus   • Female  has  no  action  of  estradiol  receptors   • Testosterone  acts  in  brain   à  estrogen  receptors  in  cell  leads  to  DNA   transcription  à  altered  brain  response   Females:   • Estrogens  are  bound  –  do  not  get  to  brain   • Binds  estrogen  in  females,  prevents  estrog en  to  act  on  estrogen   receptors                          
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