398 



GENETICS OF FISH 



About 1921 

 WILD X WILD 



WILD WILD WILD WILD 



WILD golden golden WILD 



1 1 



2a golden X golden 



I golden golden golden golden | | albino 



1 1 



3 (Done in 1940) golden X »lbino 



1 



Ahait 1934 

 WILD X WILD 

 I 



WILD WILD WILD WILD 

 WILD albino albino WILD 



albino X albino 



albino albino albuio I 



HISTORY OF SEPARATION AND 



REUNION OF COLOR GENES IN 



THE SWORDTAIL 



This chart shows the independent origin of the golden 

 and the albino and the results obtained when these 

 mutations were crossed. The backcrosses of the 

 "synthetic" wilds to golden and albinos show the genetic 

 structure of these differences. Some of the discrepancies 

 in the ratios in the backcross and F2 results may be 

 accounted for by the differential viability of the three 

 types of swordtails. The albino is the weakest, and the 

 golden is definitely weaker than the wild type. The 

 total of 3S4 F2 offspring is made up of the progeny of 

 several females. Some Fi matings produced F2 young 

 in the ratio of 9:3:4 so closely as to be remarkable. 



;>>x<^r^ 



Gold moihcr •iil 



Stippled daugbten Sm 



JUi Slippled aona 



^ Sf Sippird M>Di 



Sttt Slipplrct Kina 

 and dau|hlcri 

 3 Stipplrd plilyhahr* - 



SiSt Slippled >oni 

 and daafhien 



This diagram illustrates the way in which the gray or stipple pattern of the platyfish is 

 inherited. In the pair on the left, the father carries the dominant factor (StSt) for stippling 

 while the mother is non-stippled (stst). The parents are designated as Pj. The first filial 

 generation (F,), obtained from this mating, are all stippled (Stst) like their father. Similar 

 results are obtained when the mother (see pair on right) is the stippled parent (StSt) and the 

 father is non-stippled. The offspring of this mating are also all stippled, this time like 

 their mother (St^). When the individuals of the first generation (Fi) ore bred together from 

 either scries, and the second generation (F2) is produced, the following results are obtained: 

 there are three stippled fishes (StSt) or (Stst) to every non-stippled one (stst). There are 

 male and female representatives in each group. This is an example of simple mendelian 

 inheritance of a single heritable character. The stippling is actually due to the presence in 

 the skin of very small black cells, technically known as micromelanophores. 



