GENERAL ZOOLOGY 



Eugenics is that particular branch of appUed genetics which deals with the 

 improvement of the mental and physical characteristics of future generations 

 of the human race. Its problems are: first, extension of our knowledge con- 

 cerning human heredity; and, second, the education of the public in an 

 appreciation of the meaning and application of this knowledge. The first of 

 these problems is very difficult. A knowledge of hereditary principles is best 

 gained from controlled and repeated experiments, which obviously cannot be 

 carried out with human beings. Thus, the social tabu against marriages 

 between near relatives is based on the knowledge that defective ofTspring 

 result if recessive genes for undesirable traits are brought together. This, of 

 course, can also occur in marriages between unrelated individuals. Inbreed- 

 ing experiments with rats conducted by Helen Dean King for many years 

 produced an unusually vigorous stock of animals. Animals having desirable 

 genes in a homozygous condition will be obtained by inbreeding if the de- 

 sirable genes are present in the beginning; neither defective nor desirable 

 genes are produced by inbreeding. In 1930 H. S. Jennings, in The Biological 

 Basis of Human Nature, pointed out the great handicaps of eugenics in the 

 light of modern knowledge of genetics. The phenomenon of dominance 

 makes heterozygous individuals appear normal, although they may transmit 

 undesirable genes. Prevention of the breeding of the socially unfit and of 

 those afflicted with uncontrollable physical or mental handicaps, desirable 

 as such a measure may seem, will not eliminate the heterozygous carriers. 



Until recently it was impossible to detect the presence of a recessive gene 

 when it was combined with its dominant allele in a heterozygous individual, 

 except by the breeding test. It has been found by using the technic of paper 

 chromatography that some products of metabolism in the cells of heterozygous 

 individuals {Drosophila and two species of plants) differ from those occurring 

 in homozygous individuals. In paper chromatography, substances in solution 

 are spot-dried on special grades of filter-type paper. Later, components of 

 these substances can be separated from one another by allowing special liquids 

 to move slowly through the paper. The dried substances redissolve and 

 migrate during the movement of the fluid. Different chemical compounds 

 are found to move at different rates and, thus separated, can be identified 

 by various methods on the redried paper. By using this technic, it is 

 possible to distinguish between fruit flies, for example, homozygous for cer- 

 tain genes and those that are heterozygous. That is, the products of metab- 

 olism in the cells of heterozygous individuals differ from those formed in 

 homozygous individuals; these compounds migrate at different rates in the 

 paper. Similar technics have been used successfully to identify children 

 carrying hereditary factors that bring about a fatal blood disease (familial 

 primary systemic amyloidosis) in adults 30 to 40 years of age, long before 

 there is any clinical indication of the disease. If these technics for the 

 detection of carriers can be extended, they will prove to be of revolutionary 

 importance in the formulation of a sound program of eugenics. 



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