Explanation Of Gene Action As Related To Physiological

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Lush: You would get some surprises always, yes. The situation in which
the cross averages half way between the two parental stocks would require
complete additive action or some special balance of the plus and minus deviations.
If you had some dominance of favorable genes, then your _cross
would be nearer the better parent.
Warren: On this problem of mortality, would you, before you went to a
test cross, exhaust the possibilities from increased exposure first or would
this be involved?
Lush: I would do whichever were cheaper and in the increased exposure
I would wonder whether the means I used for increasing exposure were the
same as the birds would encounter on the farm.
We had a case one time, I do not know whether it still holds up or not,
on the leucosis thing where the injection of leucosls into the peritoneal
cavity increased the leucosls very greatly, but there was practically no
correlation between the amount of leucosls in the injected half and the uninjected
half of the same family. At the time it looked like the injection
by-passed the natural mechanisms of resistance. In the next trial the
causative agent was just put in the nostrils of the bird. This did increase
!
the incidence in the inoculated birds and it did give a high correlation be-
tween the inoculated and the uninoculated halves of the same family, The
intraperltoneal method did not look as if it were getting us anywhere.
Because of such experiences when one increases the exposure, he needs to ask
himself: Is my method of increasing mortality one which tests more strictly
the natural mechanisms that _might be built up genetically or am I by-passlng
them and not doing any good?
If such a method were cheaper, and I were not by-passlng the natural
mechanisms of resistance, I think that might be cheaper than using special
tester stocks in Progeny tests.