﻿HERITABLE 
  VARIATIONS 
  — 
  MULLER 
  347 
  

  

  chance 
  to 
  grow 
  back 
  to 
  their 
  original 
  size. 
  Thus 
  it 
  results 
  that 
  every 
  

   cell 
  of 
  the 
  body 
  has 
  the 
  same 
  kinds 
  and 
  numbers 
  of 
  chromosomes 
  and 
  

   genes 
  as 
  the 
  fertilized 
  egg 
  had, 
  and 
  as 
  every 
  other 
  cell 
  in 
  the 
  body 
  has. 
  

   The 
  original 
  two 
  sets 
  of 
  genes 
  of 
  the 
  fertilized 
  egg 
  — 
  one 
  set 
  received 
  

   from 
  the 
  sperm 
  of 
  the 
  father, 
  the 
  other 
  similar 
  set 
  derived 
  from 
  

   what 
  the 
  egg 
  of 
  the 
  mother 
  contained 
  before 
  fertilization 
  — 
  are 
  still 
  

   both 
  present 
  in 
  every 
  cell 
  of 
  you. 
  But 
  these 
  two 
  sets 
  of 
  genes 
  of 
  the 
  

   fertilized 
  egg 
  were 
  all, 
  and 
  more, 
  that 
  were 
  needed 
  to 
  result 
  in 
  a 
  

   complete 
  man. 
  We 
  see, 
  then, 
  that 
  every 
  single 
  cell 
  of 
  you 
  in 
  the 
  

   skin, 
  the 
  brain, 
  or 
  anywhere 
  else, 
  contains 
  the 
  makings 
  of 
  a 
  complete 
  

   man 
  or 
  woman, 
  and 
  that 
  you 
  are 
  in 
  this 
  sense 
  wrapped 
  up 
  within 
  

   yourself 
  many 
  trillion 
  fold. 
  Not 
  each 
  cell 
  may 
  grow 
  up 
  into 
  an 
  entire 
  

   man, 
  of 
  course, 
  but 
  must 
  remain 
  content 
  to 
  do 
  its 
  specialized 
  share, 
  

   even 
  though 
  it 
  has 
  a 
  full 
  cargo 
  of 
  genes, 
  because 
  its 
  structure 
  and 
  

   activities 
  are 
  Hmited 
  and 
  regulated 
  in 
  various 
  ways 
  through 
  the 
  

   mutual 
  influences 
  received 
  from 
  the 
  other 
  cells 
  in 
  the 
  body. 
  The 
  

   various 
  cells 
  of 
  difl'erent 
  organs 
  developed 
  differently 
  from 
  one 
  another 
  

   because, 
  though 
  possessing 
  the 
  same 
  genes, 
  they 
  found 
  themselves 
  in 
  

   different 
  situations 
  subject 
  to 
  different 
  influences 
  from 
  the 
  start. 
  

   Only 
  the 
  egg 
  and 
  sperm 
  cells 
  then 
  may 
  eventually 
  realize 
  anything 
  

   like 
  their 
  full 
  potentiahties. 
  

  

  All 
  this 
  explanation, 
  somewhat 
  oft' 
  the 
  main 
  theme, 
  will 
  serve 
  to 
  

   furnish 
  some 
  notion 
  of 
  how 
  the 
  characteristics, 
  in 
  fact 
  the 
  entire 
  sub- 
  

   stance, 
  of 
  any 
  human 
  or 
  other 
  living 
  being 
  depend 
  upon 
  its 
  genes, 
  

   acting 
  in 
  a 
  chemically 
  coordinated 
  fashion. 
  So 
  complicated 
  is 
  the 
  

   manner 
  in 
  which 
  the 
  products 
  of 
  the 
  different 
  genes 
  react 
  with 
  one 
  

   anothrr 
  that 
  no 
  final 
  product 
  and 
  no 
  characteristic 
  of 
  the 
  adult 
  body 
  

   is 
  due 
  to 
  any 
  one 
  specific 
  gene, 
  but 
  in 
  the 
  production 
  of 
  every 
  organ, 
  

   tissue, 
  or 
  characteristic, 
  numerous 
  genes 
  take 
  part. 
  Nevertheless, 
  if 
  

   one 
  individual 
  differs 
  from 
  another 
  individual 
  in 
  regard 
  to 
  just 
  one 
  

   of 
  the 
  genes 
  that 
  do 
  take 
  part, 
  it 
  will 
  be 
  seen 
  that 
  the 
  given 
  character- 
  

   istic 
  in 
  the 
  two 
  individuals 
  will 
  be 
  different, 
  and 
  so, 
  conversely, 
  a 
  differ- 
  

   ence 
  between 
  two 
  individuals 
  in 
  regard 
  to 
  a 
  certain 
  characteristic, 
  

   let 
  us 
  say 
  eye 
  color, 
  may 
  be 
  due 
  to 
  a 
  difference 
  between 
  just 
  two 
  given 
  

   genes 
  in 
  them 
  rather 
  than 
  other 
  genes. 
  We 
  may 
  then 
  call 
  these 
  for 
  

   short 
  the 
  genes 
  "for 
  brown" 
  and 
  "for 
  blue" 
  eyes, 
  respectively, 
  while 
  

   remembering 
  that 
  really 
  in 
  both 
  individuals 
  many 
  other 
  genes 
  are 
  

   present 
  also 
  which 
  are 
  helping 
  to 
  produce 
  the 
  exact 
  eye 
  colorations 
  

   seen, 
  but 
  that 
  these 
  other 
  genes 
  happen 
  to 
  be 
  alike 
  in 
  the 
  two 
  individ- 
  

   uals 
  in 
  question, 
  and 
  therefore 
  are 
  not 
  causing 
  this 
  particular 
  differ- 
  

   ence 
  between 
  this 
  brown 
  eye 
  and 
  this 
  blue 
  eye. 
  

  

  By 
  studying 
  the 
  characteristics 
  that 
  appear 
  among 
  the 
  descendants 
  

   in 
  later 
  generations, 
  after 
  individuals 
  differing 
  in 
  regard 
  to 
  one 
  or 
  more 
  

   genes 
  have 
  crossed 
  together, 
  the 
  definite 
  Mendehan 
  laws 
  and 
  the 
  laws 
  

   of 
  linkage, 
  governing 
  the 
  handing 
  down 
  of 
  genes 
  from 
  one 
  generation 
  

  

  