26

was extensively investiration, no gametes carrying a new modification of it
that alters its capacity of action have yet been identified, however, in
a few plants and kernels having it, sectors showing the Spm-s capacity have
appeared but their frequency is low, In contrast, another Spm-w isolate
exhibits relatively frequent returns to or twoard the Spm-s type

capacity of action,

e). Transvosition of Spm

Initially, the most complellinr evidence of unit elements, indenendent
of the gene but capable of controlling its action. came from discovery of
their transposition from onelLocation to another in the chromosome
complemamt without Loskag pecificity of action in the process. trans-
positicn is aibehavioral mechanism that all of them may share in common,
lowever, in studies of this, it was learned that an element known to be
transposible, may not undergo transvosition within a given set of
conditions, When these conditions anply, it could be difficult to
detcrmine whether or not the observed altered phenotypes wers the result

te pinnae

of action of a controlling element, emof gene mutation, er of a
A
Vinge 5 1
modifier or a mutator-gene, In the cascs we have examined, this could

be distinguished on the basis of known histories of origin and of

of comparitive behaviors under given conditions, In other words,
transposition makes possible ready identification of a controlling element

but lack of evidence of this does not “exchhdey necessarily) the possibility

that a controlling element is responsible for observed types of mutation

2i\Berunr
or of instability of gene aetion, There is evidence to suggest that

controlling elements in maize may plag a larger vart in the origin of
mutants than hes previously been suspected, and this will be considered in
the concluding section of this report,

Evidence of transposition of Spm is extensive, +t has been observed
in various types of experiment conducted. for purposes other than that of
examining the phenomenon of transposition itself, tests conducted for the
latter purpose reveal more about it than evidence, however,extensive,
obtained from other types of tests, Therefore, in this report, only
those tests will be reported in detail that are centered on an examination
of trans’: sition of Spm, Bown nen . uetolee

There is no doub1t that the time during development and the frecuency

Ua 7 7 quot
ot _oceurrence—ef transpesition of Spm ase under some form of control, suer

. PL Aline m-1 m=1
as the time and frecuency of mutation at ay and Bo are controlleg be

A
dL ove pris
the state that is present in any one plant or kernel, Up to now, the
A

conditions responsible for suek control¢ have not been ‘kéertttfter’ and no

 
28

tests have been conducted that might serve to reveal them, although such
are possible, Nevertheless, it is suspected that the control may reside
in the Spy element itself, and that changes in this may reflect some
alteration that occurf@Ato this element, Even though an examination of

wor 1 pol cob
factors associated with control of transposition of Spm were negleeted,
the following types of control are known, With some isolates of Spm,
transposition of it occurs in some cells early in plant development.
With others, th&s occurs only late in development o> ya th still others,
transpositions may occur both early and late in development, With sib
other isolates, transnosition of Spm, either early or late, may occur only
very rarely, With one isolate, no evidence of transposition has yet been
obtained although it has received extensive study.

Well autced _ stuey
Tee Spm smwetem is not ideal Tor exemining the mechanism associated
A
with transvosition, This is more readily accom»lished with other systems anc
4
That of Ds or of Ac at the P or Bzyz loc¥ serve this purpose better, No
oy Use

additional evidence of the mechanism imveived has come from this study of

Spm,
2g

f). Modifier element in the Spm system

In the course of study of aml, a series of tests were being conducted

\ ;
to determineSpm number and location in aearly a thousand (995) plants,
all of wich were derived from the second generation backcross to plants

that were homozygous for the standard a. locus and in which no Spm was

L

m=,
present. The state of ay was the same in all plants that carried it.

The behavior of this state with a fully active Spm is shown in photogranh

d

With this—steate, mutations occur late in development of both plant and

wer bone Ok a Uy ia Couaog u ubh
kernel, with few excentions, E i , it would be expected to
“4
was . Buuseaht plant

pe stable in expression in successive generations, and t-is was Bound to be
A

\

true. In fact, although it has been used very extensively in these

Rowlor Wau Leon Aecoceun yo?

Studies, no gamese carrying a newly altered state of it DAS appocwed in any
one of the 2
test. However, ag plants in the test seris menticned above that was
m=]. : :
ay [a4 and carried one Spm element in chromosome 5, was crossed by one

that was homozygous for ay and had no Spm. On the resulting car,mfxkhix

m=
all a, 1 caVrying kernels that also had Spm exhibited the expected

pattern of mutation to A, wkkk that this state produces with the exception

Rous

oy
of one, This exceptional kernel exhibited a markedty increased number of
A

A; mutant spots in comparison with that shown by the other varicgated kernels

QAR -

ALR . $ .
on the ear,(andtaic—is illustrated’ photograph’ ). Its phe otype
. A
30

suggested that an alteration of state of a had occurred in an
ancestor cell cnet petduecd this kernel. Theplant derived from this
kernel likewise exhibited tha same marked increase in frecuency of
mutation, Tests we-e conducted with this plant in order to examine the
nature of the altered phenotype, and these indicated that the increased
mutation rate was not the consequence of an altered state of a but
rather of the presence of an independently located heritable unit,

The effect on a.™1

1 mutation rates produced by this heritable unit could be

seen only when an active Spm element was also present in the chromosome
complement, In the absence of Spm, or when it is inactive, no evidence
of the present of this Modifier is noted. Tests of it conducted in
subsequent plant generations indicated that it underwent freauent
transposition and thus, could be considered as an independent controlling
element within the Som system, Its presence in any one kernel or plant
could be detected readily by the increase in rate of mutation to Ay

it effects with those states of at that are charact: rized by the
production of relatively few such mutations in its absence, This, rate

er tleett nwt Curd Vy Hod

of increase of mutation is proportional with esaeh state in that the

anon Dring “uch ottug > =
number of mutant spots is increased by a factor somwhere between 2 and 3,
i, A
Lous ,

The time when mutations occur is not altered by this element, Also, on
/

tf /% coy
31

in the presence of

states of a wet that give very many mutati ns to A)

active Som, this element appoars to exert 1l&ttle or no effect, Atee,
gt frere is no evidence to indicate that increased doses of it will effect
et
\e a proportional increase in rate of mutation,

Tests of the action of the Modifier on four states of ant were
conducted, In addition, tests of its transposition were made, Likewise,
its behavior was examined with a fully active Spm-s element, an Spm-w
element and also ones that are undergoing freauent change in phase of
activity. It is of interest to note that it produces the same
phenotype with either Spm-s or Spm-w,

No more is known of the origin of the Modifier other than that
steted above, nor has another instance of origin of it been noted,
qt could be related both to the Spm element, since it enhances Spm-w
activity, and to the element at amt, since it exhibits one of the

properties of this element, that is, control of rateof mutation to Al.
32

&)e Resume of mode of operation of the Spm system
“rom the descroptions given in the preceeding parts of this secti Ny
the reader may have gained the impression that the Spm system of control
of gene action is inordinataly complex, “here is no doubt that the
analysis of a system of this type may be inordinately frustrating because
may

of the many mamkraxx diverse phenotypes that/anpear even in different

: : : O-
parts of an individual plant or in different aress of eme kernel, and also

 

because of the irregular and irreconcilable ratios of

phenotypes that may appear in progeny of sister plants or even in progeny

Uwe iat

derived from different parts of the same plant, becuuse of this, study

ote, Aeiguay

of at had to be discontinued for a period as no effeatixve interpretations
A

Ame . . mi=1

was-orawn from observations and tests of it. Study of a, progressed

more rapidly and successfully;and relatively ecrly in its stugg, inter-

pretations could be drawn of the basic mode of operation of the elements

ett cs a a .
involved in this system and these have remained (essentially valid for all
et A AGE (ebay
observations and tests subsequently ecnducted,
A
ofirrcetioy
For a ready appreciation of the mode of alets of this system, an

Ya The first is
understanding only of two primary aspects are essential, Wrexexaxe

concerned with eam-umerstendinge-ef-the expressior given by, the different

states of a tt and agi, and the second is concerned with the basie mode
Lo
oo

Ockwu be independently located
of oentesi-wiuthieciy the/Spm element. All other aspects are secondary

in that they are concerned almost exclusively with the degree of effectivey
ressof action of the Spm element at any one time, and the conseauences of

this with any cne state, These secondary aspects,nevetheless, are

apparent
responsible for much of the/immadédmetve complexity of this system jend

wa COMAnd &
for many. of the difficulttes and frustrations experience in its analysis,

¥

. : me] m=1
As mentioned earlier, the states of a, and a, control the
. c.

types of mutation, the time of their occurrence, and the frequency of this
at any one stage in develipment when Spm is present and active. they

also control the tyne of gene exvression that appears in the absence of Spm,
The states vary greatly with regard to these expressions, Thus, within

the system, diverse plyenotyves are produced that are attributible ‘hn,

Quo Subbed ~ eth eit ose, arty &

to state differences, The—primery—action-ef Spm , $6—~a » porosesellie

sexe ea a ae Si a
m1 peut w ras

inductidh ef changes at the a, ~~ or a, | Lowey that jeadte altered

wi
pheastest: expressiongof qeogedd Included among them are mutations to

stable alleles either to a totally recessive, a, or a >? or to higher

Vay Product wry 4 wor be bua

alleles,taath associated with a particular typnetand degree of predtetien
A A

 

of anthycyanin pigment, aAngznerxehangex Anothcr ons equence of tee

er Bite OO - Tat dyes qe *
changef-—thet Spm induces oe Eee a wt Ov a! regrets not im muiation-+o-&

Lz
O moydfeeatin
Awad Ut

QO stable allele, but rather @® an altered tyne of behsvior of the locus in

subsequent cell and plant generations both in the presence and absence of

Spm, that is, to a change in its state,

: wee

aw dite, + ay

a
j

* ws

A “

, v .
. tape’
qhpn, fear baa OL hors
\ x.
. fe fee Deer As
i, eu y

35

m=-1

Part II. Origin and Behavior of ay

1. Origin of a,™? and of its different states.

The origin of a7? was outlined in the trevious section. It first
appeared in a single kernel on an ear produced by the cross of a plant
homozygous for ay and for A, to one which was A, /a, and ho/ Ay The a5
in this latter plant had been derived from mutation of ant to the
stable recessive, Ane All of the kernels on the ear, except one,
were either uniformly dark pigmented (A, and Ay) or totally colorless
(Ay> oe The exceptional kernel had spots of deep pigmentation in a
colorless background. The plant derived from it (culture number 5371)
likewise exhibited variegation for anthocyanin pigmentation. It had
& number of distinct areas of deep pigmentation in a non=pigmented
background. From the known constitutionsof the parents, it was suspected
that the instability of genic expression was associated with an alteration
that had occurred at the Al locus in the heterozygous parent and in a
single cell, late in development of the plant. Therefore the variegated
plant was crossed with a nymber of plants that were homozygous for the
standard recessive, a+ It was also crossed with plants homozygous for

Ay oD Lanuney cone

the standard recessive, a ana for mwtkzr recessiveg alleles of other
A

genes known to be involved in development of anthocyanin pigment formation.
9
r act POS
©

36

From these crosses it was readily determined that the variegated plant
carried the standard recessive, ass in one chromosome 3, and a recently

modified Ay locus in the homologue, and that the modified locus was

responsible for the expression of variegation. This locus was given the

designation a=. The original variegated plant, 5371, carried the

standard Ay in one chromosome 5 and a stable recessive, Bos derived from

mutation of ast, in the homologue.

On the ears pppduced by the cross of the original amt plant to
plants homozygous for ay and A,» kernels exhibiting several different
phenotypes appeared: those that were uniformly and deeply pigmented, those
that were uniformly but lightly pigmented, those that had areas of deep ot
ayn h Cok were

light pigmentation in a colorless background, and totally colorless , kepnets.
A

The types of pigmented areas and the pateéerns of these were much alike

megs otk a)
among the variegated kernels. There were some large areas that were

A

old
either deeply pigmented or more lightly pigmented and many small areas
A
with these pigment types, as illustrated in photo. e However, on
a few ears, there were one or several kernels that exhibited a pattern of
alo:

variegation that differea markedly, Some had only small spots of deep

pigmentation in a colorless background, and the number of these ranged

from only a few in some kernels to very many in others. Other exceptional
37
kernels exhibited pigmented areas of various sizes in which the intensity
was always low.
Kernels exhibiting different phenotypes were selected from some
ears and planted in the greehhouse the following winter, 1950-51. The
phenotypes of tye selected kernels are entered in colugn 1 of table 1.
The phenotype exhibited by each plant was similar to that expressed in
the kernel from which each was derived. For example, if the kernel had
Shown only a few small spots of deep pigmentation in a colorless background,
the plant likewise showed only a relatively few small streaks in which the
onto by diy
deep pigmentation appeared. Or, a plant derived from a variegated kernel
A
having pigmented ares whose i-tensity was low, likewise exhibited pigmented
areas in which the grade of intensity of this was low. It was evident
that the altered patterns of variegation in the selected kernels and in
the plants derived from them arose as a consequence of some genetic
dip |
modification controlling timeq durpng develo »ment at which change in gene
A
Spe
action occurs, iw numbers of cells in which such changed occurs at any one
time, ar ie types of pigmentation that would result from this.
Confirmation of this precise type of control of gene action came from
tests conducted with these phants, through self-pollination of them and

through crosses of them to plants that were homozygous for the standard

recessive, a,. The phenotypes of the variegated kernels on the ears
38

these crosses produced resembled that which had been expressed in the
kernel from which each plant had arisen,

The kernels selected for greenhouse planting belonged to several
different categories, enumerated in table l. All four plants derived
from kernls in row 1 carried a stable A, mutant of am. Those
derived from the uniformly pale colored kernels in row 2 appeared to

carry a stable intermediate allele of AL from tests conducted with them in

the greenhouse. Subsequent tests conducted with their progeny indicated,

pik

that the am locus in them was unmodified and that it would express

the original type of variegation pattern in the presence of 5pm. Tests
of one of them, plant 5700A, and of its progeny will be consiaered in
detail later. The two kernels in row 3 had been selected because each
exhibited a few small colorless areas in what appeared to be a fully
pigmented background. Tests conducted with them indicated,-howexer, that
this phenotype was not produced by somatically occurring change in gene
action from A, to ay but rather it was produced by a very large number of

late occurring mutations frumx to Ay
38

  
   
  
   
    
 
 
 
 

- of kernels that appeared o rived fyém self-polYination of

 

 
  
   
  
   
  
 
  
 

d arisen, |

i yet y

" t ZW

For ¢ th ‘peeenhouse ple iting, e-—few kernels

i

RMN eee.

e selected thet appocared

Oph: Cacd To be CRews Vetta)

a fully pigmented Packer unde

O

$e exhibit a few smafil colorless areas i

A

Tests of the planté derived from them indicated, however, that thaD

Comin, ‘t

phenot: pe was no~ produced by acnange n gene expression from the Avtype

to vay, but rather wes due to a very large number of lsete occurring
A

“Lees MA, anult w what oppentebe &  . y
mutations to Ay. Wasa tint g~Seemna,

Tense anes pha S—opmecr
oF sateen pete. sae tae sos Made |

mutation to | Viut_sathon from-coritivence-of piprente

Wap bower pabunt of

areas, lhis confluence doss not exstsee fmom direct contact of one mutant

 

area with another but rather of, spread of some substance , produced in the

CLD iS
rar FN A, mutant areas Sato the surrounding genetically a, aEers that allows

she Lett »

pigment to be formed in trem, This substance may spread through a number
Ad o Pequarag eio8 OLY EHUs ua 0. VMHNL Uli bew rie \
of cells and it gives rise to a halo about cach genotionliy Ay mutant |
“
OL Jun wit Cater
axea, the intensity of p&gment decreasing as the distance from the mecent

bye WA uu cad £0 Ns Qe rose )

@eea incresses,. Thus, whenever a large number of chosely placed mutant

~,
39

WH

A, areas are formed, confluence of their halos occurs andxknixxnxmiuees
A

Rokhxknxkexrneixanixpiankyx When this oeoles within a hkarge area of a
plant or kernel, the area may appear to be uniformly pigmented and to

have arisen from an early occurring mutation to Al. However, microscopic

Qar

examination of such area$ usually reveales some irregularities within it in

A a
“ur weula be 4g.
grades of intensity of pigmentation, Suckh—ts expected :

soe Dra, Siby orton bet, burs ufos wo

confluence) embetes

~

prcuul Vubonatty ig Cou ao wt eyrasuval
Halos of the type described above ane—not—pretteod—by mbent are s

pigment
exhibiting Vsccmsena OCMC REE mivoned ties of lower grade. The borders

ausy

fens arvees are sharply defined. Thus, a change in gene action at

 

 

amt to full Aj- type expression may be distinguished from those that

“eS
give Besser intensity of pigmentation not only on the basis of HO
Aho pacauond ut oY Pvabwecr. che 4

intensity, but also on the basis of AVaLOSs Poumetton . It is suspected that

APs at

ROWL,..
the pigment produced in tre:se-caited pale areas is not the same as that
Ova Home LAredbure oy Uy will be Woy Later.

produced by the standard Aly Thiete—shew—monecleanly in-ske—ptort—tian

New, cnrderced Lprobting or UE Oop peer va plautt»
in the-kesmel , In them, the pale-paadpeaing phenotyne is “expressed only

‘ i v wathtty ~
in some tissues and is conspicuoukly absent from the leaf-blade except af
A

the mid-rib, In contrast, the full A, phenotype is wemdiky expressed

INF AR Ul Leerg 2. puored willy,
in the teaf-blade, | Also, in the plant, some of the pale-producing

mutants give rise to anthocyanin pigments with pastel shades that obviously
1.0
would not anpear morely from reduction in amount of the same pigment thjat

is produced we stand rd A,. It is likely that the action of the pale
1

POAT wr unit
mutnts peodvees pigments that differ fromthat ax standard “A
Tu

rt tantd -demived—fnem g_ m1

is_,resermt or
. 2 oe

 

wv 4 Achayer,

In addition to the cases of modified a” action theat—reseut+—tr-the

oS
32

described above, tests were conducted with 3¢

 

other plants grown in the greenhouse during the winter of 1950-51,

C Row, Ghee 1)

Four of them ,were derived from kernels that apneared to be uniformly

Wd when
pignentedy the t:pe beim similar to that produced y standard A, is

LU Ub uy (ot Cuonan

present, In the ne rorenveE txvec of them, the stahel Ay ‘phen of: pe appeared

Oud Yow agen wo ocelot 2 witobi “* Zapoucuon. oer (diay hd ee 3
urth :

in expected proportions}, vy, The To a modified Be

Wemubpr Viyaydur 4 Fy beta mud QuXantee that
. behovies-in—theat—ht pramineed very many mutetions pmer a
A

-A

V

development, It is probable, therefore, that the phenotype of the

by

kernel that gave rise to this plant was produced bY conflvence of haloes

whe Munn CRow2, Gabe \)

about mudant APCAS yam described above, Five other plants, ech derived

from a kernel exhibiting only pale pigmentation, uniformly distributed

a

over the aleuron layer, were also examined. fhe pale phenotype appeared
fer. %. ae

¢
to be quite stahle in expression and was regovered in expected proportion.

in Bee progeny derived from tests crosses made with each of tnese plants.”

Wo AMC Lied renee op fronted .
LL

: Se dee “pal . * . Tre .
a Ye eccalae ywil |
| athe 0 Whi dyn’

In addition, tests were conduct d with JQ plants, each demived from a

CRow 4, per) *

variegated k=:rnel, Five came from kernels that had exhibited the pattern
A
variegated
of this that was common to the majority of/kernels om ears produced

m=

by test crosses conducted with the original a, carrving plant. mach

of the remaining 14 vlants came from a kernel that had exhibited some
from
marked deviation g# this patterm, and the types of this are described in
ny 5&0 & ~ | 7 :
,colum 1 of table 1, In this table, the culture numberg of each plant

are “Fam tt Wn
is given, and that of four of them rasxkemn underlined, *becse—_fetie—roerrs
Ougualzel -

anethe sounes-ef four of the six modified states of at ' that were used

'
j bm

m=.
extensively throughout the study of ay ° In subsequent refcrences to
mle
a particular state, it will be designated by the number of the plant wetek

Wnt rwuwd

originally carried it, It may be sete at this time that although

o: t Sat
the original state of a has given rise to many different states
© L g & 3

\b adi CLA | oof.
only a smeii—nepressntative sample of types hag reeaived=fult examination.
clear wdeadion
No exidense of a two-element system, responsible for control of gene
A

* was obtained from ratios of kernel types on ears

expression at ay
produced by self-pollination or by test cross of the olants grown in the

@reenhouse during the wintexof 1950-51.

  

whiely wi il
\ —

th had] vers

vw
ent

acai
f

¢ AMY

X

proces oe

om

TL RG
RE:

f

pend

he

Examples illustrating this are given in table 2, In this table, the
of kernels ex
phenotypes/produced by tests crosses conducted with the plants entered in

7 wy )
line 4-5F-* of table 1 are onbocta. All of tae variegated plants were

kernels derived from

m-1 7 ay, Ao/Ao in constitution, In thts tableg, the progeny/feem any one

ay

are
test xm divided into three classes; kum uniformly pigmented, kexnuixyxkkE

variegated, kzxnmkay and khe colorless, kxxneks The intensity of pigment

2 Ddetod by

pf\ kernels @ntered in the uniformly pigmented class differed according to

<haX woo

the vlant tested. Those derived from tests of plant 5S715A were intensely
A

pigmented, The xmkenxkkyxek pigment in those derived from plants

was (ee Ip butu Woe lial fon dade

S@%17A, S719A-1, and 5719A-2 . In contrast, the

 

“| 4

knkenskkyxef kernels in this class in the progeny of plants 671LE and
5718 expressed a very low level ofVintensity ef pigment. Theywe-e R11 wy
very pale,

Similarly, differences were expressed in the pattern of variegation

w tho Wollus Oy. UWA Dylowd me NBUT Te ABC 1.
exhibited by kernels in the variegated class, In the progeny of plant

. A
nrerne colld Rurvelo vey. deeply-

57158, these were characterized by the presence a many, small/pigmented
A

spots. ao @ few kernels, a large/pigmented area wes —produssd. The pattern
A

given by the variegated class of kernels in the progeny of plants5719A-1 and

5719A-2 were alike, and it resembled that given by plant 5715A except that

Oh
there were far fewer i onted svots, Plants 57174 and 5718 produced
A
4.3

variegated kernels in their progeny that had small, deerly pigmented

Lye
spots but the numbers of them were Tower than those in the variegated class

d\ produeed—by plants 5719A-1 and 571°A-2 and Blso no large vigmented areas
appeared an any of them, The pattern exhibited by the variegated kernels

in the progeny of vlant 571LE was likewise distinctive, Onig_emeaa ty
spots of deep pigmentation aprmenredin-shem and these were di +
A

lignthy over the aleurone layer,

Tests subsequently conduced with the progeny of the plants entered
at 4 pout S713 Qud S29A-1
in table 2,-- and s through many plant generations-- indicated

that the pattern of variegation given by each was a reflection of DWE

modification that had occurred to ant in a cell of the original a

carrying plant. This was responsible for the altered pattern of
A

m=]

expression of a,™ given by each of the plants entered in table 2,

It is known that this expression will persist through-cetd-—er plant

in some cell of a plant that again
generations until another event occurs/¢e modify#the beh vior of a
rie nok ba AM r 1
and this,will be expressed

ins t cell;and-siant gonesations, that the degree of stabilit
oD boyd aa 6 7
Whsud>, ww party onthe

of any one state of amt through plant generations bs—reistied—+o time of
Dye)

occu rence of mutation-inducing events, -- those that produced the deevly
A

m=.

pigmented spots in the progeny tests just described,-=-will be pointed out

LAs It need only be stated here that the later the time during
by

development that such mutations occur, the less the change of appearance

od OL

in a gamete of a newlv altored state, /Rewly altsred states must be present

on~
in gametes if it is to be isolated for further examination,

Plant 5720, row 9, table 1, arose from a kernel that exhibited both

large and small pignented are’ s in a colorless background but the intensity

Caer Be
CAL BM a

of pigment in all of them was much lower than that produced by Ay. The
4

different areas exhibited pigment of quite diffe ent intensititée, ranging

duh

from very pale in some to quite imtesse in others, The plant also
P\ ot OLED
exhibited vex ; in which different grades of intensity we-c expressed.

Progeny of this plant, derived from self-pollination and from reciprocal

crosses with plants homozygous for ay and y produced variegated kernels

a hour

of the same type as thet which gave rise tc this plant, In seme of them,
“A

however, one or several small spots of the full A, -type pigment anne red,
A

PACHULT G Dve. Quod. wil ew
In addition, there were many kernels exhibiting uniformly distributed
“A
A Pp (que dt
piewemt over all oi the aleurone layer, and the intensity of this ranged
A

from very light in some kernels to yakte derk in others, These keznels

Weg 24 prsaatel
expressed Qmong them the same grades of pigment intensities as that
A
the pigmented @
exhibited among/different/areas in the variegated k rnelf, There were also

a number of colorless kernels. Subsequent study of the progeny of plant

5720 made it evident that a modification of a me=1 hed occurred in a
1
fo
U1

1 parent
sporogenous or spore cell of the criginal aun carrying/plant that had

effected a marked shift in the proportions of different mutant phenotypes
akatec &

it would produce in comparison with thabegiven b’ the original ay
A

m=1

However, this alteration did not rmaeb the time during develovment at

which a mutation-inducing event would occur, as it had done <RxXknE EREEX

uxerthedxahoye with resvect to zh a, carried in the plants entered

row
in kime 7, table 1, dustridbed above,

As mentioned earlier, none of the tests conducted with plants
Gave Onallite) cugguius
grown in the greenhouse during the winter of 1950-51 tmdtested the

presence of an indbpendently located element that was associated with wulyf

expression of gene’ " fppedeadod desler a 2) m=1, Only He svoceny of some of thes
Dromwuod gus) dug Eyt. rnol Ly lowes.
3 Tea

greenhouse plants were gwama fluring the summer of 1951 was

crf Wes obanuc :

 

y
a x
the type Sinsdenn ee eis will be considered below, Sie

oo 4
eee mation ont Lcatn) wut st
Dee ee 56 or of crepersthestatag —
During the summer of 1951, pinirpeene songs a oon reoeeny. denived
Cruprlr Covdludot uyuth earn
pen fFom five of the plants entered in table 1, 5700A, 5716, STLIA~1, $719A- 2;
Une gage. pe UAE ue anole shal

and 5720. In addition, kernels were selected from ears produced by
A A

 
     

 

 

cross of the original ami carrving plant (5381) to plants that were {
. Se . ~
homozygous for a5 ° Among the latter, ther~ wereh6-plants derived -frem ~
f ct

kernels exhibiting the nattern of variegation appearing in most of the
kernels receiving art from the parent vlant, lh plants derived from
kernels whose variegated patterns deviated markedly from this, 7 plants
derived from kernels fat appeared to be fully A, in phenotype, and 7
other plants derived from kernels that were uniformly but less intensely
pigmented,

i= A record was made of the phenotype exhibited by each plant and test

crosses were conducted with each,

 

with one? that w&W homozygous for the standserd recessive, &@;, and for the
recessive, sho (shrunken endosperm) which is very closely linked to ars
giving only 0.4 percent recombination with it. This stock had been

obtained from Dr. M.M.Rhoades for the purpose of making m more accurate

, Qe tA Lata
dufforou ae hy: wy mae a A bint aehwi
examinations of the | tepes-ef-behavios. Of. anetabinity, 6 y, A,~-—_Imdondadentiy

arising Bases of this had been. scoumlating, ~ Close linkage of a well
, 4 . : a
expressed gene marker with & unetabke locus would allow accurate
detestion M21. nuyalow | Nip
xdemkitinakion of some types of genekiz change in sere action ofthe

| u
unetabbeteeus that otherwise might not be detected, Since all a,
A ,

WM]

plants grown in the summer of 1951 were homozygous for Shay erosses of them

with plants homozygous for az and sho, preparded the way for more
Ovw-\ Coe
precise investigations of #6 in the future. Othrer—tests—of these nlants
7
Uste -
wn oeolTiny , ee Wrede Lott
teeo—were meade, 5 ere self-pollinated, and WRilso crossed te:
a _, Bongphests were s Pp ,

A
ibe 4 ah

m ° oe
plants carrying other states of ay 1 4 op-be—these derived from the—pete

 

class of kesnets;, Howdves, Wt thes time, other projects were in progress

that took precidence ofver theximmediate—econtiemred study of amt and

MBE wn Tag Quer A aS |
therefore, the ears obtained from the various types of cross were not
“A

carefully examined until more than a year had elapsed, Included in these

7 m- m—
™ oa a a and ay 4

other projects was examination of the behavior of a 1

L

three independent incevtions of instability uxpxmsskenx of gene expression

at the locus of Aji, It was soon realized that ismekaktkiky cortrotof

me 3 me), WO tot acbea '-
1

gene expression at aj and a residedt-im the Ds-Ac system,of-contme+

ef—_sone—ecettion, The system controlling ame wes not Ds-Ac, nor that

having operation
in which Dt is involved, A system wkkk a quite di*’ferent mode of azkion

. : Ss . :
was responsible for its teemes=m@ exvressions An interpretation of the

mode of opsration of this system was formulated from tests cpap 4 with

clung rp pleecaluug Gyr ebloee otsReeuel feud / oie!

it overapeniocdof EBTee | Years, even Resulis of test ebteined curing
wash how

Ea na ie

yeas Comune Wee you Cd Secrets 9/123

 
     

m=]

   
 

RVLLINnt IA, to ta today yb ,
Sumer, it—r@es—susrected that the system operating at bei a, me
9 8S y aS —

Aimulonr ty Dat Ure ug WUkuk gy urodbun oxa,™ Trudy op acm
might be themeome Qubsecuent temes indicated, however, that this

assumption was incorrect, The two svystens do not have elements in common
7
Ure

L8

nor is their mode of operation compsrable,

. m1
Even thovgh a decision had been made to postpone study of ay

until more time would be available for its examinaticn, it was desired to

lezrn if the change at A,, responsible for the origin of ay, would of ut
wr 4 | |

alter crossing-over between this modified locus and sh To determine

this, only a few vlants would be required and only a small amount of time

To .
need be given to aecomptish the test. Therefore, 10 variegated kernels

were removed from an ear produced by each of two variegated vlants that

on CoA lun

when pollen from a plant homoz gous for a_ and sh

Wty Me=7
were a, Sh,/a, Sh 7 5

Dipad beer Hach of the two

wes used on the silks of each ear, Rath variegated plants had been

derived from a variegated kernel on the ear vroduced by the cross oBfnducted
“Untrt ne {yoda o4 Whew ‘vod the STIQR-~ akoall of Pe

with. plant 5719A-1, entcored in C of table ee Nineteen mature plants
were obtained “rom the 20 selected kernels. All exhibited variegation
m1

for anthoeyanin pigment, and all were ay Sho/a, sh, in constitution,

2

The silks of ati ears produced by 17 of these plants received nollen from
plants that were homozygous for ay and for sho. The reciprocal cross
Variegated

was conducted with 8 of these/plants. The kernel types appeartbng

on the cars these crosses produced are entered in table Be
a RUNS

ne

ray

1

aye,
\ MA pe ,

49

. Su. ed ir Clasioo col
gyudon a wh \yo Wow 5 VAAL

Sy °. oo ea power
In ‘table bs very close linkage le-oxsnessed between | ‘Sh2 and the CHOSE 3

QL Curblen On econ Pigeamr

m. Within the 71,90 kernels that exhibited

 
     

pigment, there were three distinct classes, In two cf them, pigment
was uniforsaly distributed over the aleurone layer. Cf the 3617 kernels
inwith tniform ai stribves ef pigment, only mere had the tyne of pigment

produced when Ay is present, The pigment in the other gkaxx 3613 kernels

oats i " Ou". ns

eben wy thy A Oe yd ut. ae wal | ar Webs, he Abou q fp ce

WAS ,Gbebinetie—dicfexent, and this was well expressed ty the @ :
hocpuibic anarboe

wixenxkekueanxkhe muxpkexf{Pr}xandxxRexandxprxcar vy Ones an pigment intensity

petwoon- dugum Ur undo Comportd Urcatt “hp norco ellyld,

xavthose that had Pr gard those that were homozygous for pr. With the
¢ “

 
  

standerd Ais the presence of Pr results in’ the production of intensely

purple pigmentg, When pr is homozygous, tie kermels exhibit with A, ,

an intense red color, Some of the a, -
na

plants had Pr in one chroriosome

5 and pr in the homologue, The aj,sh, tester plants were homozygous for pr.

2

Therefore, on scthe of the ears, half of the kernels carrged Pr and the

other half was homozygous for pr. On these ears, it was very evident

for, |
UA a viru wn a regula

that the intensity of pigment appe ‘ring | the uniforly pate class of _kernetis

(ae “pole Pinas ua Val? 3)

q depended upon their constitution with respect to the alleles of Pr,

The color in those kernels having Pr was a deep purple, almost as intense

as that produced when the standard Ay is present, Gm-the-etrer-heand,—they

kesnets-tnit were homozypous for pr.were.only
50

In contrast, those homozygous for pr were a very light shade of pink,

dh i
: It was apparent that the pigment present in the pale class of kernels
A

augeped Dp yivamere po. difyeet
did not represent dilutionjf that produced by Ab but mathor a dissinettve
Rarer Recrvmnds ous; id wtb rele elheo Oneynd, Wiser tor

were alike in
A

et

tyne of pirment.

 

“henotrpic expression and,akam all those that were pr were mkmkkikx

&
likewise alike, The pale class represented, then, one particular

' pigment type in the
genotype. Among the variegated class of kernels, the/suwksxm? deeply

pigmented spotsypesembled that produced by Als either a very deep purple

or a very deep red depending on the presence or absence of Pr in them,
+ "yh, - an ~~ A A -
C Va, pute aduume, pr acesorun olicll, 2d obrune, “Docalied ua duu pne's.) La)

The pattern of such spots was quite similar in all but a very few kernels,

yw 7 { L2e (O90 op Cm. AY pha aA wp pote oyu Caton oo duduh a de Lite ilar br AY ana? be + cust]
Illustrations of this pattern are g’ ven in photo e
In examining the data of table 3, attention should be given to the
different
ratio of the pale class to the variegated class apnearing on/ears
ya mal
Dp. plant, and on these ea derived from use of its pollen in
(= p Peace Aarne es 40
™ the test cross to 81 Shoe Ly may be seen that an approximate ratio of 1
me A
~ pale to 1 variegated kernel apveared on ears produced by tests crosses
os
is conducted with ~lants 1,2,l, 5, 6, 7, and 8 4 culture 652 and by
(>

[.

plants 1, 2, R, 5, 6, 7, and 8 in culture 6453 although there are some
marked deviations from this exrressed by tests of the pollen of plants

62-5 and 6453-. The ratio of pale to variegated kernels derived from