Tae Golden tge of Com Genetics at Comell

as seen through the eyes of HM. M. Rhoedes

aize Genetics at Cornell besan in 191 when R. A. Emerson came from Nebraska
to head the Department of Plant Breeding. Hmphasic in those early days was on
Such bessic genetic problems as the location 0. numerous unplaced genes, factor
interaction, establishment of linkage groups, linkage maps, pericarp variegation,

the inheritance of gametophytic caaracters, the cenetic basis of seml-sterility,
etc. Smerson's mesterful analysis of the inheritance of plant colors did more

than any other single paner to plece maize genetics on a firm basis, Huchn was
leamed at Cornell about the composition and architecture of the maize genome by
mmerson, dutcainson, Demerec, “. %, Anderson, Lindstrom, “yster, Sprasuc, Phipps,
Li, Brunson, Brecger, Fraser, anong others, The importance of these early
investigetions cannot be over-emphesized, They set the stage for the remarkable
advances in cytogenetics which followed, The extogeneticists stood on the shoulders
of their predecessors,

Prior to the mid 1920's, little cytological work was done with maize, which
was not regarded as favorable cytological material, This was an erroneous con-
clusion, icClintock, using the carmine smear technique invented by Belling,
found thet the pachytene chronosomes could be accurately identificd by length,
arm ratios, and heterochroratic knobs in specific locations, Maize was an excellent
organism for both cytological and genetical studies and the combination of the two
disciplines (cytogenetics) quickly led to a large number of significant studies,
Maize cytogenetics may be said to have begun in 1929 when icClintock's paper on
triploid maize appeared in Genetics, Thet progress was explosive in the next few
years is evident from the following account of the advences made in the subsequent

Six years,
~ln

The status of maize cytovenetics by tne mid 1930's was summarized in the

paper b:r Rhoades and iicOlintock published in The Botanical Review in 1935, The

accomplishments described below were lergely taken from that paper although a

few researcn findings, more genetical than cytogenetical in nature, ere included.

Tae names of tne investigators resnonsible Sor each advance are indicated in

perentheses, Capital letters designate those individuals who were trained or

were postaoctoral fellows at Cornell.

The Status of Maize Genetics in 1935,

Le The establisiment of ten Linkage groups corresponding to the 10 chromosomes
of the haploid complement. (Cooperative studies by many, mostly American,
ceneticists).

fe The association of each linkage group with a particular, morcholocically
identifiable member oi the chromosome complement, (McCLINTOCK, Brink, and
BURSHAM).«

Be The placement of specific senes at definite vositions within the physical
chromosome, (IMcCLINTOCK and others),

he The cytological proof of genetic crossing over (CREIGHTON and McCLINTOCK),.

Be Cytological and genetic proof of chromatid crossing over (MeCLINTOCK, RHOADS),

6, Cytological deternination of the physicel location within the chromosomes of
reciprocal translocations, inversions and deficiencies, (McCLINTOCK, BURNHAM,
Brink, CRYICHTON, RHO'DES, V, H. RHOADS),

Te The genic control of chromosome behavior, (B‘ADLE, MeCLINTOCK).

8. Proof that chiasmata are points of genetic crossing over. (BEADLE).

9. Nonhomologous pairing and its genetic consequences, (McCLINTOCK, Stadler),

10, Instability of ring-shaped chromosomes leading to variegation. (MeCLINTOCK).

ll, Divisibility of centric regions, (McCLINTOCK).
le. Correlation of heteropycnosis with genetic inertness, (RANDOLPH).

13. Artifical production of polyploidy. (RAIDOLPH).

14. Mutagenic effects of X-irradiation. (Stadler),

15. Cytological and genetical analysis of Zea-Uuchlama hybrids (EMERSON, BSADLS,
Hangelsdor’ and Reeves),

16.

oO

yoological studies with Zea-Tripsacum hybrids. (Mangelsdorf, Reeves),

17. Cytoplasmic male sterility. (RHO"D™S),

The above compilation indicetes the prominent role that Comellians played
in the development of maize cytogenetics, ‘The period from 1929-1935 was truly
the Colden Age of Maize Genetics at Cornell. The achievements of the Cornell
group in the 1920's and 1930's wes wurivaled by any other constellation of vlant
geneticists and was second only to the famous Drosopnila school under Norgan at
Columbia,

Adding to Cornell's reputation was the establisnment at Ithaca of the
Maize Genetics Stock Center for the maintenance end distribution of genetic stocks
end the founding of the Maize Genetics Cooperstion News Letter, in which appeared
unpublished data unselfishly contributed by geneticists at many institutions. This

unique cooperstive effort was so successful that it became widely copied,