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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  19 
  2 
  9 
  

  

  the 
  cell. 
  Moreover, 
  the 
  genes 
  in 
  different 
  chromosomes 
  are 
  different 
  

   from 
  one 
  another, 
  except 
  in 
  the 
  case 
  of 
  homologous 
  or 
  twin 
  chromo- 
  

   somes, 
  i. 
  e., 
  the 
  corresponding 
  chromosomes 
  which 
  each 
  cell 
  of 
  an 
  

   individual 
  received 
  from 
  the 
  father 
  and 
  from 
  the 
  mother 
  of 
  the 
  indi- 
  

   vidual, 
  respectively. 
  To 
  match 
  each 
  chromosome 
  that 
  was 
  derived 
  

   from 
  your 
  father, 
  every 
  cell 
  of 
  you 
  has 
  in 
  it 
  also 
  a 
  similar 
  chromo- 
  

   some 
  (though 
  not 
  necessarily 
  quite 
  identical) 
  derived 
  from 
  your 
  

   mother, 
  so 
  that 
  it 
  contains 
  in 
  all 
  two 
  complete 
  sets 
  of 
  chromosomes 
  

   and 
  hence 
  two 
  complete 
  sets 
  of 
  genes. 
  The 
  proper 
  functioning 
  of 
  the 
  

   cell 
  during 
  its 
  life 
  depends 
  upon 
  the 
  proper 
  cooperative 
  functioning 
  of 
  

   its 
  thousands 
  of 
  different 
  genes. 
  One 
  complete 
  set 
  of 
  genes 
  would 
  

   ordinarily 
  be 
  enough 
  for 
  this, 
  but 
  two 
  sets 
  are 
  provided 
  so 
  that 
  new 
  

   combinations 
  of 
  the 
  characteristics 
  of 
  different 
  ancestors 
  may 
  be 
  tried 
  

   out. 
  

  

  Each 
  given 
  gene 
  in 
  the 
  cell 
  must 
  of 
  course 
  have 
  its 
  own 
  specific 
  

   chemical 
  composition, 
  differing 
  from 
  gene 
  to 
  gene, 
  though 
  there 
  is, 
  no 
  

   doubt, 
  a 
  chemical 
  relationship 
  between 
  all 
  genes. 
  As 
  yet, 
  however, 
  

   we 
  have 
  no 
  knowledge 
  as 
  to 
  what 
  the 
  chemical 
  composition 
  of 
  any 
  

   individual 
  gene, 
  or 
  of 
  genes 
  as 
  a 
  group, 
  is. 
  Whatever 
  it 
  is, 
  we 
  can 
  

   not 
  escape 
  the 
  fact 
  that 
  the 
  different 
  genes, 
  through 
  differing 
  chemical 
  

   reactions 
  with 
  other 
  substances 
  in 
  the 
  cell, 
  produce 
  by-products 
  

   which 
  have 
  a 
  very 
  profound 
  influence 
  upon 
  the 
  properties 
  of 
  the 
  pro- 
  

   toplasm. 
  And 
  through 
  the 
  combined 
  influences 
  of 
  all 
  the 
  chemical 
  

   products 
  of 
  the 
  thousands 
  of 
  different 
  genes 
  in 
  a 
  cell, 
  meeting 
  one 
  an- 
  

   other 
  in 
  the 
  common 
  protoplasm 
  and 
  then 
  interacting 
  in 
  devious 
  ways 
  

   to 
  form 
  further 
  products 
  again, 
  the 
  exact 
  form 
  and 
  physical 
  and 
  chem- 
  

   ical 
  characteristics 
  of 
  all 
  parts 
  of 
  the 
  cell 
  that 
  contains 
  those 
  genes 
  

   will 
  be 
  determined, 
  for 
  any 
  given 
  set 
  of 
  outer 
  conditions. 
  Changing 
  

   conditions 
  external 
  to 
  the 
  cell 
  will, 
  of 
  course, 
  change 
  the 
  properties 
  of 
  

   the 
  protoplasm, 
  too, 
  but 
  what 
  form 
  and 
  behavior 
  it 
  can 
  and 
  will 
  show 
  

   for 
  a 
  given 
  set 
  of 
  outer 
  conditions 
  depends 
  primarily 
  upon 
  what 
  

   genes 
  it 
  has. 
  Since 
  the 
  body 
  of 
  a 
  man 
  or 
  other 
  animal, 
  or 
  a 
  plant, 
  is 
  

   made 
  up 
  of 
  its 
  cells, 
  and 
  the 
  form 
  and 
  other 
  properties 
  of 
  that 
  body 
  

   depend 
  upon 
  the 
  properties 
  of 
  these 
  constituent 
  cells 
  — 
  their 
  form, 
  the 
  

   way 
  they 
  fit 
  together 
  and 
  work 
  — 
  it 
  is 
  evident 
  that, 
  less 
  directly 
  but 
  

   no 
  less 
  surely 
  than 
  in 
  the 
  case 
  of 
  the 
  individual 
  cells, 
  the 
  character- 
  

   istics 
  of 
  the 
  whole 
  body 
  depend 
  upon 
  the 
  nature 
  of 
  the 
  genes 
  in 
  the 
  

   individual 
  cells. 
  

  

  These 
  individual 
  cells 
  of 
  the 
  body 
  have, 
  during 
  the 
  development 
  of 
  

   the 
  embryo, 
  been 
  derived 
  from 
  an 
  origiaal 
  fertilized-egg 
  cell, 
  through 
  

   a 
  succession 
  of 
  cell 
  divisions 
  in 
  the 
  course 
  of 
  each 
  of 
  which 
  every 
  

   chromosome 
  and 
  every 
  gene 
  present 
  in 
  the 
  dividing 
  cell 
  also 
  divided 
  

   in 
  half, 
  one 
  half 
  of 
  every 
  chromosome 
  and 
  gene 
  then 
  entering 
  one 
  of 
  the 
  

   two 
  daughter 
  cells 
  and 
  the 
  other 
  half 
  entering 
  the 
  other 
  daughter 
  

   cell. 
  Between 
  divisions 
  the 
  chromosomes 
  and 
  genes 
  usually 
  had 
  a 
  

  

  