﻿GENETIC 
  PROGRESS 
  — 
  EAST. 
  295 
  

  

  to 
  believe 
  that 
  dominance 
  of 
  " 
  A 
  " 
  over 
  " 
  a 
  " 
  was 
  due 
  to 
  actual 
  ab- 
  

   sence 
  of 
  any 
  function 
  of 
  " 
  a," 
  or 
  even 
  to 
  the 
  physical 
  absence 
  of 
  any 
  

   gene 
  whatsoever. 
  Now 
  we 
  have 
  come 
  to 
  see 
  that 
  dominance 
  is 
  a 
  

   mere 
  arbitrary 
  measurement 
  of 
  the 
  approach 
  of 
  the 
  result 
  "Aa 
  " 
  to 
  

   that 
  of 
  "AA" 
  or 
  " 
  aa." 
  This 
  has 
  been 
  brought 
  about 
  by 
  finding 
  

   cases 
  in 
  which 
  the 
  effect 
  " 
  A 
  " 
  or 
  " 
  a 
  " 
  in 
  the 
  haploid 
  condition 
  could 
  

   be 
  compared 
  with 
  the 
  effects 
  of 
  " 
  AA," 
  or 
  " 
  Aa 
  " 
  and 
  of 
  " 
  aa." 
  

   These 
  cases 
  make 
  it 
  seem 
  doubtful 
  whether 
  the 
  association 
  of 
  "A" 
  

   with 
  " 
  a 
  " 
  ever 
  wholly 
  inactivates 
  the 
  latter. 
  

  

  With 
  this 
  conception 
  of 
  the 
  function 
  of 
  the 
  genes 
  in 
  mind 
  it 
  is 
  

   possible 
  to 
  work 
  out 
  pretty 
  definitely 
  the 
  actual 
  resultant 
  onto- 
  

   genetic 
  characters 
  after 
  different 
  matings, 
  both 
  with 
  and 
  without 
  

   linkage, 
  by 
  applying 
  the 
  laws 
  I 
  have 
  just 
  discussed. 
  It 
  is 
  merely 
  a 
  

   straight 
  mathematical 
  relationship 
  following 
  immediately 
  after 
  ac- 
  

   ceptance 
  of 
  these 
  basic 
  conclusions. 
  But 
  there 
  are 
  several 
  difficulties 
  

   involved 
  in 
  identifying 
  the 
  concrete 
  results 
  of 
  breeding 
  with 
  the 
  

   abstract 
  results 
  of 
  calculation. 
  Some 
  of 
  these 
  difficulties 
  have 
  been 
  

   leveled, 
  others 
  are 
  yet 
  to 
  be 
  overcome. 
  

  

  One 
  must 
  realize 
  that 
  each 
  gene 
  has 
  many 
  effects 
  on 
  the 
  organism, 
  

   some 
  of 
  which 
  are 
  not 
  easily 
  discoverable. 
  The 
  fact 
  that 
  a 
  gene 
  is 
  

   usually 
  ticketed 
  with 
  a 
  name 
  indicative 
  of 
  its 
  most 
  obvious 
  effect 
  on 
  

   a 
  particular 
  character, 
  should 
  not 
  mislead 
  us 
  in 
  this 
  regard. 
  Then, 
  

   too, 
  one 
  must 
  remember 
  that 
  many 
  genes 
  affect 
  each 
  organic 
  char- 
  

   acter; 
  and 
  that 
  similar 
  characters, 
  characters 
  apparently 
  identical, 
  

   do 
  not 
  necessarily 
  owe 
  their 
  qualities 
  to 
  the 
  same 
  combination 
  of 
  

   genes. 
  And, 
  finally, 
  it 
  does 
  not 
  follow 
  from 
  any 
  of 
  the 
  above 
  rela- 
  

   tions, 
  what 
  will 
  be 
  the 
  result 
  of 
  gene 
  interaction. 
  The 
  action 
  of 
  

   two 
  or 
  more 
  genes 
  may 
  be 
  necessary 
  to 
  bring 
  about 
  a 
  visible 
  or 
  

   measurable 
  result, 
  though 
  these 
  genes 
  may 
  be 
  carried 
  along 
  sep- 
  

   arately 
  generation 
  after 
  generation. 
  The 
  full 
  logic 
  of 
  this 
  fact 
  

   tears 
  down 
  the 
  veil 
  from 
  many 
  an 
  obscure 
  result; 
  since 
  the 
  difficulty 
  

   of 
  appreciating 
  the 
  results 
  of 
  selection 
  has 
  been 
  due 
  to 
  the 
  failure 
  to 
  

   realize 
  how 
  many 
  modifying 
  genes 
  may 
  be 
  carried 
  along 
  which 
  

   have 
  no 
  chance 
  to 
  produce 
  a 
  measurable 
  effect 
  unless 
  a 
  certain 
  basic 
  

   gene 
  complex 
  necessary 
  for 
  particular 
  organic 
  expression 
  is 
  also 
  

   present. 
  

  

  This 
  short 
  sketch 
  will 
  show, 
  I 
  hope, 
  that 
  in 
  the 
  21 
  years 
  of 
  ex- 
  

   perimental 
  genetics 
  real 
  progress 
  has 
  been 
  made. 
  To 
  be 
  sure, 
  this 
  

   resume 
  has 
  been 
  a 
  leaping 
  from 
  crag 
  to 
  crag. 
  No 
  more 
  was 
  possible 
  

   within 
  the 
  editorial 
  limits 
  here 
  allotted. 
  But 
  if 
  one 
  recalls 
  the 
  

   scorn 
  of 
  50 
  years 
  ago 
  should 
  a 
  daring 
  seer 
  have 
  predicted 
  such 
  a 
  

   triumph 
  for 
  quantitative 
  mechanical 
  analysis 
  in 
  a 
  subject 
  so 
  over- 
  

   strewn 
  with 
  variable 
  factors, 
  he 
  in 
  turn 
  will 
  scorn 
  the 
  Freudian 
  over- 
  

   compensation 
  of 
  to-day's 
  critic 
  who 
  makes 
  the 
  taunt 
  that 
  it 
  shall 
  go 
  

   no 
  further. 
  

  

  