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GENETICS OF FISH 



Mexican platyfish, Platypoecilus maculatus. The fish on the 

 left is a female spotted (and stippled) platy. On the right, the 

 fish is the gold platy. When these two fishes are mated, the 

 inheritances of the spotted character may be traced through the 

 succeeding generations. For results of a cross of this type, see 

 the accompanying diagram. Photograph by Myron Gordon. 

 (From Fraser and Gordon. ) 



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A. Photomicrograph made by a double exposure. A partially 

 contracted large black pigment cell (macromelanophore) is 

 superimposed upon a partially expanded one. The limits of the 

 first are contained within the circle. In the contracted state, 

 note the narrow black processes formed by the pigment particles. 

 In the expanded condition the pigment particles are arranged in 

 sheets. It is by a process of pigment cell expansion and contrac- 

 tion that color changes in fishes take place. B. This picture is 

 a photomicrograph of the black pigment cells of the spotted and 

 stippled platyfish. The spots of the platy are due to large black 

 cells called macromelanophores. The gray ground color of the 

 platy is due to the smaller pigment cells, micromelonophores. 

 Note the blood vessel which reaches each pigment cell, both the 

 large end the small. Photographs by Myron Gordon. 



