Explanation Of Gene Action As Related To Physiological

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22- would intercross with each other and with Q the other families which cross reasonably well with the same families with which Q crosses well. From such intercrosses we would make new familes and then would test these new families by using them, in place of Q, in the crosses Where Q had beenmoderately successful. This is, after all, only the common sense method of testing the new families in the very crosses in which their descendants are to be used. In summary, special tester stocks on which to progeny test the stud candidates can be useful in three genetic situations. The first is when a prime object is to uncover and discard undesir" able recesslves. A current example is in testing beef cattle for whether they can transmit dwarfness. At present it is often profitable to maintain a special tester group of cows known to have produced dwarf calves an% therefore, to be heterozygous. Rarely is a recessive important enough and abundant enough to justify maintaining a special tester stock for this purpose. The senond situation is that of threshold effects where one wants to know how much margin of resistance or factor of safety is in the various animals or families which are candidates for the stud pens. For both of these two purposes, the goal is an improved pure stock. It is rarely possible to keep several different special tester strains, --- a different one for each important deleterious recessive or threshold character, perhaps, --- which might be of concern. This can be overcome in part by testing the males on their own daughters or on their sisters but the harmful phenotypic effects of inbreeding would make one count carefully before doing this. The third case in which progeny testing on special tester stocks is likely to be worth while is when overdomlnance (or "specific combining
"_3- ability" in general) is important. In this case, one is improving the lines to get still better results when they are used in a continued outbreeding program, --- not for their own qualities or for commercial use when bred pure. If some kind fairy would promiseto answer for me four questions about practical animal breeding, my choice of questions would be: 1. How important is overdominance? 2. How important are interactions between heredity and environment? 3. How important is eoistasis of the threshold or "factor of safety" kind? 4. How important are other epistatic actions? It is likely that these questions have somewhat different answers for different species and perhaps even under different systems of agriculture or different climates.
Page 1 and 2: "7-. J _ Gene Action as Related to
Page 3 and 4: dominance in their primary effects
Page 5 and 6: -ll- ! SUB-DIVISION OR CLASSIFICATI
Page 7 and 8: -13- A glance at this table reveals
Page 9 and 10: -15- genes have manyeffects, althou
Page 11 and 12: -I7- r effect of the gene, we also
Page 13 and 14: -19- be continued for several gener
Page 15: • -21- strains were very large. I
Page 19 and 20: -25- Wyatt: I would llke to ask Dr.
Page 21 and 22: -27- ! weakness in your stock you w
Page 23 and 24: -29- Hogsett: Dickerson: Dr. Dicker
Page 25 and 26: -31° We used to teach our classes
Page 27: -3_ that the pathogen, being a viru

Explanation Of Gene Action As Related To Physiological

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