280 PHYSIOLOGIC GENETICS 



embryos. The end results of either primary or secondary genie effects may be identical, 

 that is, impairment of fertility, but the immediate endocrine causes of these effects are 

 completely different. 



The majority of the crucial reproductive events are governed by several interacting 

 hormones or by overlapping series of hormones. The genetic mechanism controlling 

 the endocrine steps in the chain of reproductive events are probably as complex as the 

 interactions between the hormones. Furthermore, the action of target-specific 

 trophic hormones may be modified by other hormones which are nonspecific for a 

 particular target organ but which, nevertheless, contribute to the euhormonal state of 

 the organism as a whole and thus govern the sensitivity of the response of the target 

 organ to its specific trophic hormone. 



In spite of these complications, several methods can be used in evaluating the role 

 of genes in the regulation of rates at which glands secrete hormones. These methods 

 include: the direct estimation of the concentration of hormones in the glands producing 

 them; the biological or chemical estimation of hormones in body fluids; the indirect 

 estimation of rates of endogenous hormonal secretion by measuring the changes they 

 produce in their specific target organs (that is, comb size, rates of ovulation, litter size, 

 and so forth); and finally, the sensitivity of end organs to injected hormones. 



DISCUSSION 



Dr. Burdette: Mr. W. K. Whitten of the Jackson Laboratory will first discuss 

 Dr. Nalbandov's paper. 



Mr. Whitten: First of all I would like to mention a small item in terminology. 

 As an Australian, part of my national heritage is the world's largest population of 

 rabbits, and young rabbits are called kittens. Dr. Nalbandov has given us a critical 

 review of the method to be used in the study of genetics of reproduction, and he has 

 illustrated this with frequent examples from his own research. I am sure that by 

 application of these techniques, much useful knowledge will be obtained. 



The next step in the problem is to identify the primary action of the genes involved, 

 and to do this we will need much more biochemical knowledge. It will be necessary 

 to know the pathways of hormonal synthesis, catabolism, and also the metabolic proc- 

 esses which they catalyze. It will also be necessary to identify the hormonal receptors 

 which probably occur on the surface of the target cells, because I feel that it is at this 

 level that the genes will have the effect. 



Some progress has been made with the metabolism of the steroid hormones, but 

 the picture is so complex that it reminds me of some of the slides presented at this 

 meeting. Possibly the hormones of the anterior pituitary are themselves the primary 

 product of the genes. This is further suggested by the fact that gonadotrophin re- 

 sembles rather closely the blood-group substance of humans. The correlation of growth 

 and gonadotrophic action which Dr. Nalbandov brought out is not a surprise to me. 

 In fact, I have always believed that these hormones were in some way linked. It is 



