Personal memo from ° . L
JOSHUA LEDERBERG Bx Uhdks —

SEP 25 1987

eae [the brfe |

 

 

Dafajets er Stare)”

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

THE ROCKEFELLER UNIVERSITY NEW YORK 10021-6399

 

No. 531] GENOTYPE CONCEPTION OF HEREDITY 148

make hypotheses as to the nature of heredity and varia-—

bility. Darwin has somewhat exaggerated the scientific
value of breeders’ testimonies, as if a breeder eo ipso
must be an expert in heredity. As to the principle of
pure lines it has been occasionally vindicated by Ger-
man authors, e. g., K. v. Riimker, that pure line breeding
is a thing old and well known. This is quite true; nearly
sixty years ago L..Vilmorin not only emphasized i ina
lucid manner the importance of pure breeding, but he
even tried a little to use his experiences theoretically..
But it can not be denied that the principle of pure lines,
as a true scientific analytical implement, as an indispen-

‘ gable method of research in heredity—not merely as a

questionable and, at any rate, unilateral and insufficient
method of practical breeding—is a novelty from recent
years. Had this analytical principle been used in the
times of Darwin, or had it even been appreciated in due
time by the biometrie school, certainly the real bearing
of selection might long since have been rightly under-
stood also by the practical breeders of pure strains. .
The genotypes may then be characterized as some-
thing fixed and may be, to a certain degree, parallelized
with the most complicated molecules of organic chem-
istry consisting of ‘‘nuclei’’ with a multitude of ‘‘side-

chains.’’ Continuing for a moment such a metaphor, we -

may even suggest that the genes may be looked upon as
analogs of the ‘‘radicals’’ or “¢gide-chains.”” ‘All suck
ideas may as yet be premature; but they are highly
favoredby-the recent researches of Miss Wheldale.

The fixity of a genotypical constitution in question is

the conception arrived at by Mendelian and pure line ©

-work. Hence there is a discontinuity between different

genotypes. This discontinuity has been energetically.

contested by several biologists, among whom Woltereck

may be pointed out as an important representative. In.

his very interesting report on experiments with Daph-
nias, Woltereck indicates, as said above, that selection
was as yet ineffective; moreover he describes a case of
discontinuous alteration of type (mutation), and his ex-

 

Phancsan TI Cin MN ¥S

No, 531] GENOTYPE CONCEPTION OF HEREDITY 153

only say that this case does not seem incompatible with
Mendelian views. It must also be borne in mind that
certainly there have been very many geunodifferences
between the differing races intercrossed in Castle’s
experiments. Hence these experiments are really operat-
ing with highly poly-heterozygotic F,-generations. And
how great influence upon dimensions (of ears and other
parts of the body) those color-determining genes may
have exercised can not be easily determined.

. As to beans, it is proved that genes, effective in color- .
reactions, may also have great influence upon the dimen-
sions and forms. So in my crosses a special factor,
which makes yellow color turn into brown and causes
violet to be turned into black, ha's a very marked influence
upon the size and form of the beans in question. Here
exact data are not necessary; the instance exemplifies the
two incident matters of fact, viz., that apparently simple
‘¢dimensional’’ or meristic characters may be determined
by several different genes, and that one sort of gene may
have influence upon several different reactions.

Then it.seems that Mendelian analysis is proceeding in
@ very prosperous way; but there may be even very
narrow. limits for this analysis: the entire organization .
may never be “segregated” into genes! But still there
is much to do in carrying through the genotype-concep-
tion as far as possible. ”

As to cytological researches the genotype-conception i is
as yet rather indifferent. Certainly the process of segre-
gation must -be a ceil-action intimately connected with
division. But all the innumerably detailed results of the
refined cytological methods of to-day dd not elucidate
anything as to segregation. It seems to the unprejudiced
observer that the much-discnssed cytological phenomena
of karyokinesis, synapsis, reduction and so on may be
regarded rather as consequences or manifestations of the
divisions, repartitions and segregations of genotypical
constituents (and all other things in the cell) than as
their canses. This view is applicable even in those cases

Be cP
“a b29)99 orre