first Lecture, Januaz oy 7, 195k.
Introduction to study of variegation in meize.

ed in ma

fte

26 =— not vrevicusly noted

 

2, Phenomenon is probavly quite general; not confined to maize,
3. Reason phenomenon not discovered earlier

a). Reahthres a particular genetic and cytolog

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factors not readily obtainable in other material,

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b), “equires a particular a-rengenent along chromosome of known "reros
affecting a pa ticular tissue,

c}. Requires favorable cytolorical corditions for detection of chrono-
Some changes.

d). type of events annesred following exzeriment never condve
utilizing a tyse of chrovsosome behavior not previously lmown, -- t)
breakare-fusion-bridge evcles,

 
 

ted before,
ne

ns drawn from studios are essentially new end different
9

S,. The newness di cult for the uninformed to evalua
> en

PPL ve
knowledge of the experiment&l procedures and the trves of o Ns Mace,

6. Published accounts are inadequate to understand methods used,

7. season for scarcity of such publications: Conelusiors sto wwtled Ce
“herefore nece ssary to make a different kinds of exmeviments s in
3 uv
% conelusicns would gna? cate were

 

order to determine if the predic
Pollowed by verificaticn,

8. any of the conelusions have been verified,

9. <dnterest exoressed by some of the staff acre thet the ernerinoenteal
methods be outlined by me,

  

big a a 5 a ' s * *
10, therefore, Beadle and Anderson rocvested thet I consider eivine a
series of talkes on my material, The special course in seneties seemed to

be a gocd place for then,

11, Intention of scries of talks: ° To develop the tevoes of ernerinent
conducted and the eonelusions Sa from them. ea To indicste in whai way
the conclusions fit with mown eviderce from other macorials,
develop the backeround for the curo-osome materials involved in th
phenomenon,

II, The major topics:

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1. “he origin of many rutetions,
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2. The chrovosonal mechanisms asso

3 a The ch PO “0
enanrvre In ceric
cells in a tissue

 

III, the beginnings o* the first scries of exneriments -- why they were
conducted,

1. Origina 1 purpore: To investisaze the genie ecrposition of onearm of
one chSomeson me -= the short arm of chromosome 9 in maize, Maize has 10
chromosomes, and c-romosome 9 is the second from the smallest.

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ons had shown:

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2. tieason for t igs exmpocriment: Previous inves

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a), Removal of minute bit of chre~atin containing the normal locus of
a known gene, When homozygous, reproduces the phenote-pic exression of
the lmown recessive:
Br
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Bm, Symbol for normal gene.
bm, browm miderib, Symbol for known recessive,
“he phenotyvre of bm: brown color in s-condar

ry ¢
Fades on exposure to light. AImost com letely cell specific
gives: -

ell wall.
2 variegation

the homozygous deficiency for BR: reproduces in all detail the
phenotype prcduced by the known recessive, bn,

b). noe the recessive, bm, either a
inactivation of Bm Or, an inactivation of Bm in
express Bm.

deficiency or an

e
the cells that normally

e
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e), Other chreracters giving seme indicaticn:
“hr. 9 short arm: Ye Cc 6Bzg We

 

Yg to yg: ye, light colored ehlorovuyill in early
lite of leaf, Yeepor at tin, ligiter near bese. Gradual davvening of
leaf as plant aves, vanid darkening of older leaves, Deficiency of Ye,

produces the very sane pnenotyne.

a

C, in combination with other know fact

LOrss produccs
color in the alevreone lever of the kern&l, Cy ve essive allele, no color
in the aleurone laver,. Deficiency of C, produces aolorless aleurone,

Bz to bz. bz, bronze, a corm liented shenotynes
Bz, dark color in aleurone, red ox» purpl@s red or purr le anthocyanin
Digment in »lant. bz, known recessive, a bronze color in the aleurone
and a bronze color in the plant, Also, variegation prodveed py loss of Bz

in combination of Bg / bz, spread of Bz’ into ba for seve al cell lavers.
Deficieney of Bz. reproduces. all phases of the vecessive MHENOUVEES’s

 
Wx to wx, Wx vesults in preduction of amylose starch in
endosnerm and rollen grain. Wx, recessive muant locus, results in
absence of sucii starch, amylopectin present. Wx stains blue with fodine,

wx steins red, Deficiency of Wx, renroduces the ex DHLENOTIDS»
d). To return to original purnose?: If the tnown mutants can be

reproduced by deficiencies; if the know mutants reveal the genetic

elements at the locus, then, removal of various bits of chromatin in the

short arm of chromosome 9, ene-by6nne, and each separately, shovld reveal
a

the genetic comosition of the short arm of ehrovos e 9 for all cases that
survive when honmozyr0us.,

e). For this test, must have a means of produci-g minute deficiencies
in one part of the cirovosome corplement -- the short arm of chro ccsome 9
in the sclectcd case,

f), The method worked out one paver: Required the use of the
chro .:osomal tyne of breakare-fusicon-bridge evcle,

2 ae s 2 s
fale he essentials of t:-is mechanism:

(1) “he constitution of the gometes. (Delails importants: given
Later,)

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Semoale ale
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(2) The fvsion of broken ends in the zygote

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fot a,

m . moa eos
(3) +he Prop-cse of tne next mitotic division

(1.) The anaphase configurations

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(5) The breaks in the bridges \. |
(6) The fusions of broken ends at telovnase
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(7) The repetition of the cycle in the succeeding div

TNT RB eet aaa

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(b). In experiment, both broken ends ave in snort arm of chronosome 9.

Continuous breakage and fusion produces duplications, deficiencies,
reduplications and reorientations: axanples:
fc), Observation: “he b.f.b. cycle can cease in some cells, Prom

then on, the broken ends behave as normal ends,

&)e The effects produced in the plants by the chromosome tope of
breskage-fusion-bridge. cycles:

(1) “he ap-eerance of the seedlings
(2) the annearance of normal annearing sectors and branches,

(3) The death of the defective branches, and the survival of the
normal branches,

(1.).fhe developmat of the normal becnehes into mature plants,

V. the cytological examinaticn of the chremosemes in the normal branches

  

A). The expected types of altora
found. Duplicaticons of sermnents
and deficiencies,

2 the gnort arn of enureatiis 9
a neernents

 

2). In addition, and this is tm-ort tant, & nucsiber of very unexpected
of rearrangements seen, These involved chreo-osone 9 and other Cnt
of the cormmlenent, Hlearranse ments occurred at particular places
chr. «somes in each case, These will be considered in eta il late
a discussion of the organization of chromosomes has been siven,

  

VI, The procedure used to find the excected new mutants:
1. Hach branch (about 1.50 branches altogeticor) self-pollinsted,

Pollen (male ganetes) placed on silks of same stalk - Pollen from
tassel placed on silks of same branch. he silks lead to the ovulte,
each ovule carries a femnle camete,
2, Hach ea

é ar resulting from self-pollination examined for murat
the kernels,

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58

3e Sarmles of kernels taken from esch ears
examined for annearance of new mutants,
new mutants would be exnected,

expected to be in short arm of

seediings grown; seedlincs
4 ;

For reasons explained earlier,

and the locus in the chr: seme co mlencnt
chre some 9,

VII. the Results: General,

1, A number of new mutants appeared, as expected, L LG
lavge number of new pheiotypes, not at all ex>ected,

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2. The unexvected phenotypes appearing in seedlings of seme evltures:

~4 ae . .
a), akarples ernels planted from one ears; seedlings appeareds

Some seedlings quite’ normal: others showed variogation for chlorophylls;

very ligat green leaves with streaks of normal green,

The pa&terns of streaking seen in the seedlings:

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b). The different types of variegation that appeared, cach in a
Separate culture derived from kernels on a single ear’

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(1). white seedling with streaks of green, pale~green; pale-grceen in
wich deep green streaks were DrESENt.,

(2), Golden color of leaf, Streaks of darker color that is lignt green,
streaks o” dark green, and strceks between light green and dark green,

(3). Whte seedlings with spots of

dark green, each susrounded by a
light green "halo",

(l.) Green leaves with stroaks of light green,

VIII. The distribution and frequency of changes in expressicn. Example:
light green to dark green: ~

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IX, ‘The amnearance of the variegetion in the older leaves of the -lant:

1. the sectors appearing in leaves derived from seedling trpe-l

c2
» +he single sectors:

(A). Lt a ctors?
Sectors with inersased fresuenc:’ of ereen streaks
Sectors with reduced frequency of green streaks
Sectors with no streaks at all
sectors of full green color - large,

(B). The "Twin-Sectors"

Pull green\=no variegation: Full green,reduced frequency of streaks:

 

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2. the appearance of such types of scctoring in the many cases esanined,

~.&). Chance §n the frequency of occurrence of mutation in progeny
derived from a single cell,

b). Change in time of mutation -- the esrly mutetic
e¢). “he relation of changes in fraquency of muita
and the rélation of mutation in one sector to chanre
s cr sector,

d), the interpretaion of the twin sector origins:
two cells produced es the result oF a single mitosis,

3e On basis of interpretation of twin sectors, the following conclusions

drawn:

a). Sone factor or factors present In a young cell that cantrols the
frequency of mutetion in the orogeny of tis cell,

b). this factor, ov thsse factors, segregate at a mitosis such that
the two sister cells differ with respect to the controlling units, This
shous up as a divference in the fresuencry of mutetion in the progeny of each,

this difterence 18 often recinvrocal,
c¢). +he mutation process also associated with a mitosis = the twin
sectors showings mitant and change in frequency of mutation:
X. Lhe conclusions from the initial observaticns:

of plants that nad undergone the c, b.f.b.cvele,

1, In progeny derived from self-pollinationsf a large number of newly
produced alterations of gene loci occurred, them (ov-r l.0 found)
were expressed as variegation resembling

mutable genes,"in their behavior,
2. +n all well examined ca
present in the seed’ ‘ngs,

i
of mutation observed,

Nany of
"

eases, a particular tree of variggation pattern

he pattern -= size and frequency as well as tyne
3. Changes occurred during the development of
leading to obvious changes in the time, trve

the plant
the descendents of this cell,

in certain cells
jyand frequency of mutation in
hh, “he anpea

rance of twinesectors siowed that
the pattern of imtation,

something present controllin
This could be altered as a conseauence of °
someting that occurred during a mitotic exvcle,.
5. Also, the mutation process itself occurred as the consequence of
sonetiing that occurrs during a mitotic evcle,
6, Therefore: If mutation process, and if control of mutation »rocess
in a developing leaf is related to the mitot
expcrinentation,

ic process, it is subject to
7. The initial purpose:

What occurs during the mitotie process that
is responsible the &he altered genic action and the alter d control of
mutation in future cell generations?

XI,

In next lecture, will take up the discovery of the chromosomal
asnects involved in the change of phenotrpe - the discover ofthe Ds -
system,

Ac