﻿Genetic 
  Segregation. 
  

  

  365 
  

  

  flax 
  (Linum 
  iisitatissimum) 
  of 
  unknown 
  origin, 
  presumably 
  a 
  stray 
  seedling 
  of 
  

   one 
  of 
  the 
  varieties 
  grown 
  for 
  oil, 
  was 
  fertilised 
  with 
  pollen 
  from 
  our 
  tall 
  

   fibre 
  strain. 
  Both 
  parents 
  breed 
  true 
  to 
  the 
  fully 
  hermaphrodite 
  condition 
  

   with 
  anthers 
  perfectly 
  formed, 
  and 
  the 
  Fi 
  plants 
  were 
  normal 
  in 
  this 
  respect. 
  

   F2 
  consisted 
  of 
  hermaphrodites, 
  and 
  a 
  recessive 
  form 
  with 
  aborted 
  anthers, 
  

   generally 
  contabeseent 
  and 
  not 
  dehiscing 
  at 
  all, 
  but 
  having 
  occasionally 
  a 
  few 
  

   grains 
  of 
  good 
  pollen. 
  The 
  ratio 
  was 
  a 
  normal 
  3 
  : 
  1. 
  The 
  recessive, 
  having 
  

   occasional 
  grains 
  of 
  pollen, 
  self-fertilised, 
  gave 
  similar 
  plants 
  with 
  anthers 
  

   wholly 
  or 
  almost 
  wholly 
  aborted. 
  The 
  normal 
  ¥ 
  2 
  hermaphrodites 
  gave 
  in 
  F 
  3 
  

   families 
  which 
  showed 
  that 
  some 
  of 
  the 
  F 
  2 
  plants 
  were 
  pure 
  normals, 
  others 
  

   heterozygous 
  in 
  the 
  ordinary 
  way. 
  But 
  when 
  the 
  recessives 
  were 
  fertilised 
  

   with 
  pollen 
  from 
  three 
  several 
  varieties 
  of 
  tall 
  fibre 
  flax, 
  only 
  recessives 
  

   were 
  produced. 
  These 
  tall 
  flaxes 
  therefore 
  are 
  normally 
  heterozygous 
  

   for 
  the 
  recessive 
  or 
  " 
  sub-female 
  " 
  condition, 
  and 
  this 
  in 
  segregation 
  is 
  

   permanently 
  relegated 
  to 
  the 
  male 
  side 
  of 
  the 
  plant, 
  while 
  the 
  female 
  

   side 
  takes 
  the 
  hermaphrodite 
  factor. 
  Segregation 
  in 
  regard 
  to 
  the 
  same 
  

   recessive 
  may 
  take 
  place 
  in 
  one 
  of 
  two 
  ways. 
  It 
  may 
  be 
  unilateral, 
  as 
  it 
  is 
  

   when 
  in 
  heterozygous 
  association 
  with 
  the 
  female 
  of 
  the 
  tall 
  flaxes, 
  or 
  it 
  may 
  

   be 
  ambilateral 
  and 
  unrestricted 
  to 
  either 
  sex 
  when 
  it 
  is 
  in 
  association 
  with 
  the 
  

   female 
  of 
  the 
  oil 
  flax. 
  We 
  must 
  infer 
  that 
  the 
  female 
  halves 
  of 
  the 
  two 
  types 
  

   differ 
  in 
  some 
  critical 
  respect 
  which 
  decides 
  the 
  manner 
  of 
  the 
  segregation. 
  

  

  Unilaterality 
  may 
  also 
  show 
  itself 
  as 
  a 
  difference 
  in 
  the 
  closeness 
  of 
  

   linkage 
  on 
  the 
  two 
  sex-sides 
  of 
  the 
  same 
  plant, 
  and 
  no 
  doubt 
  this 
  fact 
  may 
  

   have 
  a 
  bearing 
  on 
  the 
  interpretation 
  of 
  the 
  foregoing 
  cases. 
  The 
  late 
  

   E. 
  P. 
  Gregory 
  discovered 
  the 
  first 
  case 
  of 
  this, 
  in 
  Primula 
  sinensis. 
  He 
  

   found 
  that 
  the 
  linkage 
  between 
  magenta 
  colour 
  and 
  short 
  style 
  was 
  closer 
  

   in 
  the 
  eggs 
  than 
  in 
  the 
  pollen. 
  Recent 
  work 
  on 
  a 
  larger 
  scale 
  has 
  given 
  

   109 
  : 
  1 
  as 
  the 
  female 
  linkage 
  and 
  6 
  - 
  4 
  : 
  1 
  for 
  the 
  pollen. 
  A 
  similar 
  difference 
  

   has 
  been 
  also 
  found 
  for 
  the 
  linkage 
  between 
  green 
  stigma 
  and 
  " 
  reddish 
  " 
  

   stem 
  (as 
  opposed 
  to 
  dark 
  red), 
  the 
  value 
  being 
  29 
  - 
  8 
  : 
  1 
  for 
  the 
  eggs 
  and 
  

   4T7 
  : 
  1 
  for 
  the 
  pollen. 
  In 
  both 
  examples, 
  individual 
  families 
  show 
  wide 
  

   fluctuations, 
  and 
  these 
  values 
  should 
  for 
  the 
  present 
  be 
  regarded 
  as 
  

   approximate 
  only. 
  Whatever 
  be 
  their 
  meaning, 
  they 
  show 
  that 
  some 
  

   segregation 
  has 
  occurred 
  in 
  the 
  formation 
  of 
  the 
  two 
  sets 
  of 
  sexual 
  organs, 
  

   such 
  that 
  the 
  process 
  of 
  gametic 
  differentiation 
  is 
  not 
  the 
  same 
  in 
  both. 
  

  

  Besides 
  these 
  examples 
  of 
  differentiation 
  between 
  the 
  male 
  and 
  female 
  

   sides, 
  there 
  are 
  others 
  proving 
  that 
  segregation 
  may 
  occur 
  at 
  other 
  stages 
  

   in 
  somatic 
  development. 
  The 
  most 
  obvious 
  examples 
  are 
  the 
  variegated 
  

   plants. 
  I 
  have 
  discussed 
  this 
  subject 
  elsewhere 
  in 
  connexion 
  with 
  reversible 
  

  

  