126

table 31).

The ratio of kernel types on the testcross ears of those plants in
the progeny of plant 6629A-8 that were Y Spm/y+ in constitution is
given in line 2 of table 31. It may be noted that the percent of recom-
-binants in the variegated class of kernels on these ears resembles that
obtained from tests of the Y Spm/y + plants in the progeny of plants
6629A-1, A-4, A-6 and A-7, discussed in the previous section and sugmarized
in table 29. Among the plants having more than one Spm in the * bearing
chromosome, different groupings with regard to position of the Spm elements
in-these--plants could be made based on the ratio of phenotypes appearing on
the testcross ears produced by cach Mey fell into two main groups, as
Shown in lines 3 and 4 of table 31. In addition, there were two plants
on whose testcross ears the ratio of kernel types did not fit that given
either in line 3 or 4 of table 31. The kernel types on the ears these
two plants produced are entered in lines 5 to 7 of this table.

From the tests conducted with the progeny of plant 6629A-8, it would
appear that this plant had one Spm element which occupied the same
position in chromosome 6 as in the four Y Spm/y + plants in culture 6629,

and that althogeeugh transposition of it away from this location occurs,

the frequency ofm=eceummence of this is not high. The second Spm element
127
in this plant, also located in the Y bearjng chromosome, appeared to undergo
more frequent transposition. This @ftem resulted in placement of it
usually at new locations within the Y bearing chromosome 6 and less
frequently at locations that do not show linkage with Y.
Progeny Test 3, figure 2

Plant 6629A-2 obviously had more than 2 Spm elements, as the

ratio of kernel types on its testcross ear, given in table 5, indicate.
dt th 7 with 7

Kernels were selected both from the. main/ ear and from the ,tiller ear of
this plant and sown in the summer of 1954. Only those phants derived from
the colorless, sh, classes were examined in detail for the Spm constitution
in each. Tests conducted with them established the fact that the parent
plant had a high number of “pm elements in it. The ten plants derived from
the colorless, sho, Y class of kernels on the tiller ear of this plant
had the Spm constitutions given in table 32. It was not ¥pssible to
establish the exact number of opm elements in plants that obviously had at
least 3 of them. More than 3 Spm elements could have been present in sma
then. It was clear, nevertheless, that in several plants, 2 Spm elements
were present, each of which was carried in the Y bearing chrozuesome 6.

In addition to these 10 plants, mentioned above, 8 other plants
derived from the colorless, sh5, y class of kernels on the tiller ear of

plant 6629A-2 were also examined for Spm constitution. Three plants had
128

1 Spm and it was not linked with either pr or wx in any one of then.
Three other plants had 2 Spm elements. In one of these plants, one of the
two Spm elements was located in its wx carrying chromosome 9, The kernel
types on the testcross ear of this plant were as folléOws: 35 pale colored
Wx, 8 pale colored wx, 47 varieg.ted Wx, and 80 variegated wx. In each
of the remaining two plants, at least 3 Spm elements were present. In
one of them an Spm element appeared to be located in the wx carrying chromo--
some 9. On its testcross ear the following phenotypes appeared among
its kernels: 21 pale colored Wx, 2 pale colored wx, 97 variegated Wx, and
117 variegated wx.
Progeny Test 4, figure 2

+n order to further investigte the location of the Spm element in
the * bearing chromosome 6 in the progeny given in table 32, twenty kernels
were selected from the variegated, Y class on the ear produced by plant
6667F~11, line 2, table 32, which was considered to be Y Spm Spm/y ++.
They were sown the following year under culture number 6884. Ninteen
of the twenty plants derived from these kernels were variegated, as

| in

expected, but one was totally pale colored and/none of the kernels on the

testcross ear of this plant was evidence given of the presence of Spm.

Testcross ears were obtained from 17 of the 19 variegated plants. They
129

fell into four groups with regard to Spm constitutions, as shown in

table 33. Three plants were Y Spm/ y +. On the testcross ears of two

of them, the ratio of kernel types, line 1, table 33, was quite similar

to that on testcross ears produced by the Y Spm/y + plants in table 30

and by the majority of their Y Spm/y + progeny, already discussed. On the
testcross ear of one plant, however, the ratio of kernel types suggested
that the “pm in it was carried in the Y bearing chromosome but at a position
closer to * than in the two Y Spm/y + sister plants (line 2, table 33).
Twelve other plants were * Spm Spm/y + + in constitution (line 3, table 33).
The two remaining plants had an Spm in the Y bearing chromosome and in
addition, another "pm element not linked with Y (line 4, table 33).

From the ear of the main stalk of plant 6629A-2 (see table 5), only
those plant that were derived from the colorless, Sho, y class of kernels
were examined for the Spm constitution in each. These were gpyown under
culture number 6668C. Among the nine plants tested in culture 6668C, two
had no Spm. Three plants had 1 Spm and in one of them, plant 66680-6,
this Spm was linked with pr in chromosome 5, as shown in line 1 of table 34.
On this ear, accurate classification for the alleles of tr and pr was not
possible for all k:rnels in the pale (no Spm) class and therefore, both

pale phenotypes are combined under the heading of "*ale". In the four
130

remaining plants, 2 Spm elements weve present and they were not linked with
each other. tn .oge of them, one of the Spm elements was linked with pr
in chromosome 5. The phenotypes of kernels on the testcross ear were
as follows: 96 pale colored (both Pr and pr included), 97 variegated, Pr,
and 145 variegated, pr. In another of the plants h:iving 2 Spm elements,
plant 6668C-~3, one of these elements was linked with wx. The kernel
types on its testcross ear are given in line 1 of table 35. Subsequent
tests conductea with the variegated kernels on this ear will be considered
shortly.
Progeny Test 5, figure 2

In order to investigate further the location of Spm in plant 6668C-—6
(line 1, table 34), and the stability of it at this location, ten kernels
were selected from the vuriegated, Pr (recombinant) class of kernels on the
ear it produced and these were sown in the summer of 1955 under culture
number 6877. Nine of the 10 plants derived from these kernels were
variegated. One, however, was totally pale pigmented. As will be shown
later, an Spm element was present in this plant but it was in its inactive
state. Testcross ears were obtained from 6 of the 9 variegated plants in
culture 6877. “n Spm was present in each but in only 3 of them was it

linked with Pr in chromosome 5. The Spm in the other three plants gave no
131

evidénce of linkage with Pr. The types of kernels on the testcross ears
produced by each of these 6 plants are given in table 34. Among the

3 plants carrying Spm in chromosome 5, the position of it within this
chromosome does notappear to be the same. Certaingly, its location in
plant 6877-4 differs from that in either plant 6877-1 or plant 6877-2.

It should be emphasized that the kernels selected from the ear of plant
6668C-6 were in a recombinant class. The recombinant classes arise from
two distinctly different events. One is typical crossing over between
homologues. The Spm is transfered from one homologue to the other without
its undergoing change in location. The second event is premeiotic
transposition of ‘pm which places it at another location in the chromosome
complement. Subse ‘uent meiotic segregation may result in its inclusiong
in a nucleus having the allele of the marker to which it was formerly
Linked’, As a general rule, within the recombinant class, increasingly
higher proportions of kernels having a transposed Spm element will be
pane the closer is Spm to the genic marker.

Progeny Test 6, figure 2

As mentioned above, plant 6668C-3 carried two Spm elements, one of
which was linked with wx in chromosome 9, as shown in line 1 of table 35
it was desired to obtain plants in which the only Spm present was carried

tn nh
13.:u-

kernel types on the testcross ears each produced indicated,  . table 35.

linked
Three plants had 2/Spm ejements but no evidence was given of linkage

of them with either Pr or Wx. One plant had 2 Spm elements, not linked
to one another nor to Pr or Wx. On’ plant had at least 3 Spm @ements.

There were so few pale colored kernels on the testcross ear of this plant

2, OW Spw yaininey : AAC rend
that evidenee-ef linkage with either Fr or Wx could not be e@etmeted.
A

Aud b

The testcross ear produced by another plant had only a small basal sector
in which variegated kernels appeared. All other kennels on this ear
were uniformly pale colored,” the phenotype produced by amt when no Spm
is present.

A total of 40 ears were obtained from the testicrosses conducted with
the variegated plants in culture 6872, just described. Five ears had
sectors in them in which all kernels were pale colored (no Spm) and they
appeired only on ears of plants in which 1 Spm was present. The rate
of appe:rance of such pale sectors was considerably higher than had been

aur? wn ude ME afcan WM
observed on testcross ears produced by le Spm:carried in #he
A ’

g 4
Awk wee ~
Y=peemieg chromosome G discussed previously, On the ears of these latter

oO shia,

plants pale sectors appeared only very infrequently. Obviously, the Spm

element in some of the plants of culture 6872 was undergoing change at—a

Ww
aac Ok ime aurine development and this was evident on the ear produced

by one of the plants in which it was located in chroz:iosome 9. It was
132

in chromosome 9. Therefore, 30 kernels were selected from the
viriegated Wx class on the ear of plant 6668C-3 and grown in the summer
of 1954 under culture number 6872. Twenty-nine of the 30 plants derived
from xthexkerneiksxanxthe these kernels were variegated but one was
uniformly pale pigmented and none of the kernels on the testcross ear it
produced gave evidence of the presence of ‘pm in this plant. Testcross
ears were obtained from 27 of the 29 variegated plants. “t could be
concluded that in 19 of these 27 plants, 1 Spm was present but it was not
linked with Wx nor with Pr. Three other plants had only 1 “pm and in

each it was linked with Wx in chromosome 9, as the
132 ly »
therefore detided to investigate further the behavior of tre Spm

located in chromosome 9.

Progeny Test 7, figure 2
The kernel types on the testcross ears produced by the three plants

in culture $6872 in wich Spm was loected in chro osome 9 are entered in

table 35, As may be noted, the percent of the recombinant classes

We wey A uh oe VU) Ler. f\ Thus
differed and in plant 6872A-12, a decided difference was expressed
A
ae *
the ear of the main stalk and that of its tiller,

s

 

It avpesred that the Spm elenent in plant 6872A-12 was undergoing change
hi
tte

in location early in development. For taisresson, Gt was decided to test
. the Wocle, & hens pat,

the beh vior of ‘tam, Spm im-it in/subsequent genezation,  Pherefere, K-rnels

were selected from the varicgated, Wx class on the esr of the main stalk

of this nlant and sown under culture number 7285 in the summer of 1956,

Thirteen plants were obtained from these kernels, Twelve of them were

variegated but one was totally pale pigmented and no evidence of the

presence of Snm was obtained from test crosses conducted with it. “ince

the purvose of tis experiment was to determine Sym number and location

in different parts of the same vlant, all fertile ears produced by eoch

WE Gente. Tye, Duet wiley wee.
plant were used in the test cross. Pollen from vlants homo _ygous for

ape ~ 1
state 5718 a, and for the recessives, pr, y, and wx, was placed on the

Byyb ve
Silks of each esr of plant. Altogether, 26 ears were obtained from

the le plants having Som, The Spm constitution and location with respect
133

Wx is summarized in table 36. In one plant, no evidence was given of
linkage of Spm with Wx in any one of the four tested parts of this plant
(plant A-7, table 36). Spm was lined with Wi in some part of the other
ll plants but not in all tested parts of each plant. It was obvious
that the Spm in these plants was undergoing change in location in
somatic cells and that the time of occurrence of this was early in
development. “or those parts of these plants in which one Spm was
present and carried in the Wx pearing curcumomome 9, tue kernel types
on each ear which gave evidence of this is shown in table 37. From the
ratio of types on these ears, it could be suspected that the Spm did not
plants
occupy the same position in chromosome 9 in all parts or even in
different parts of the same plant. The kernel types appearing on each of
the 9 other ears obtained from the plants in which Spm was present are
given in summary form in table 38.
Progeny Tests 8, 10, 11, and 13, figure 2

The early occurring transposition of Spm in plants in culture 7285
was so strikingly expressed that it was decided to continue investigation
of its behavior in plants of the following generation. For this purpose,

varieg ted kernels in the Wx class were selected from the four ears

indicated by footnotes in table 37, and these were sown under the
134

given culture numbers in the summer of 1957. Thirty seven plants were
obtained from them. Thirty~six¢ of these plants were variegated. One,
however, was totally pale colored and no evidence of Spm appeared among
the kernels on the testcross ear it produced. All fertile ears of each
plant were used for the testcross. The Spm constitution in the tested
parts of these plants is summarized in thable 39. Again, in this
generation, early occurring transposition of Spm was noted. The
henotypes of kernels on ears produced by those parts of a plant that had
Som, carried in the Wx bearing chromosome 9, are entered in table 40,
and a summ.ry of all others is given in table 41.

The behavior of the isolate of Spm that was present in the plants
just described, was consistent with respect to time of occurrence of
transposition. “t was occurring in some cells early in plant development.
Other isolates of Spm differ in this respect and, as mentioned above,
early occurring transposition of it in the Y Spm/y + plants, previously
described, was infrequent. Among 40 Y Spm/y + plants in which more
than one part of a plant was tested,for Spm constitutinn, only 1 case of
change in Spm was noted and this was produced by inactivation of it

rather than by its transposition. The Spm at the given location in
135

in chromosome 6 does undergo transposition, however, but the time of
occurrence of this was usually late in plant develppment rather than
early in development.

The frequency of occurrence of transposition at any one time appears
to differ with different isolates of Spm. “or some of them, this is
quite infrequent in that only rarely is a case of transposition detected
either in the plant or in the gametes it produces. With some other
isolates, on the other hand, a burst of transpositions occurs in sporogen-
ous or spore cells. As a consequence, a lirge fraction of the Spm
carrying gametes of such plants hive a néwly trans»osed Spm in them.

But, before examples of this are discussed, another experiment of small
scope, conducted with the Spm element that was present in plants of
culture 7285 (tables 36 to 39) will be described.

Progeny Test 9, figure 2

The plants in culture 7330 (table 40) were derived from variegated,
Wx kernels on the second ear of the main stalk of plant 7$85A-1
(table 37). The Spm in this part of the plant was carried in its Wx
bearing chromosome 9. In the tiller of this plant, one Spm element was
present but on the testcross ear it produced, no evidence was given of

linkage of it with Wx. It was desired to examine the Spm constitution
136

in different parts of plants derived from variegated Wx kernels on this
ih Spm

tilfer ear in order to determine if/any of them linkage of Wx with Wx

would be found. Eleven plants, all of which were variegated, were

grown from such kernels under culture number 7331. (See line 1, table

42 for the kernel types on the sar from which these kernels were selected.)

Testcrosses were made with all fertile ears of each of these ll plants.

Only one ear was obtained from 5 plants and one Spm, not linked with Wx,

was present in the part of each plant that produced an eur. Another

plant produced 4 fertile ears. One Spm was present in the four tested

parts of this plant and in no part was it linked with Wx. The kernel

types on the ears these 6 plants produced are entered in line 2 of table

42. Some part of each of the five other plants in culture 7331 had more

than one Spm element in it, as shown in lines 3 to 8 of table 42. One of

the tillers of plant 7331B-5, however, had only one ‘pm in it.
1365

Sy axcept for the ear of one tiller of plent 5, the ratiosof kernel tres on
ears produced bv diffe ent mrts of each vlant in culture 7331 that hed

more than one Som clement in it were very much alike, Differences in

ct
ioe
pe
tr
tS

espect¢ were expressed betveen olants, hovever,. the number of
plants tested and the number of tests eccnducted with e:ch plant are too
few to draw definite conclusi ns regarding the beh: vior of this Sor
following its transposition in a somatic cell of slant 7285A-1 from a

position in chrovcsome 9, giving linkare with “x, to a new location in the

u

chromosome cormlenent. It is evident, nevertheless, that subsequent

~
_

- en i

transposition of it occured bes t

 

appe-»q—to be sedueed, | la-ty-ntsoterident—_the+—deenene—ef hentai in
Ayrton wo Care oth uy rowed wi de

culture..7331 -did—e transposition’ return 46 to a vosition in chrovos:ne 9

4

that showed linkare with Wx,

 
  
 
  

Rabgmy Bor es deur

—— one
That transnosition of Spm from A location wkexerxkkxinxxmkaxixetx

Bkahkke to a new location Get result in marked change in time and frequency
qpbetyunil oO,

of occurrence of trans osition was strikingly exprsssed in one case,

\

ey

In part II of tris renort, tests co ducted wits the progeny of the Y Spm /

y + plants of culture 65629A were considered , im=ste+l. There it was

RTALO df

pointed out that the k-rnel tynes on each of two test cross ears produced

by mlant 6666C-7 in the progeny of plant 6629A-1 wae quite aberrant and
137

AG 29. Ap pce Ag aw Ayn Lhe APacuel yee
HK did not eonfoum with al obtained from t esvg ef the majority of ~lants

in this progeny (sec passs—t=sae-tt-or cable 26), It was decided,

are

of lant 6666C-7 whose kernel tyres”

therefore, to examine some of the progeny ony thete rfentered in
pest—H oof table 26, Iwo variegated kernels in the ¥ class on tnis ear
and 3 variegated k:rnels in the y classwere grown,under culture numbers
6895A and 6895B in the summer of 1955, Tests of the Spm constitution of
each of tne five plants derived from them wave suprising results. One
Spm was present in plant 6895A-1 and it was closely linked to Y. On the
test cross ear of this plant there were 167 pale colored kernels of which
10 were Y and 157 were y,and 162 variegated ke.nels of which 153 were Y and
9 wore y. In addition, there was a small sector in which only pale coloved

kernels ann reds 21 kernels in this sector were Y and 26 were Ve

Plant 6895A-2 had 2 Spm elements, one of which was carried in its

li ove la, weal Apel
Me
Y bearing chromosome 6, In additicn to one keznel hawing a mutent of ay 1
A A J

there weve 91 pale colored kernels of which 39 were Y and 107 were Ys

OM VEN oe CGT PAE es oy Wha 130 wie oa v0 Tere eg. -
Aa dots, .
Noghinkare eae witnatr or with ‘ix was eiven.
Sayre > PiLyud Spun cle-cuout

Plant 6895B-1 apparently had one Spm and it was not linked tc either
J lit UGLY 9 .
a m=1

Pr or Wx. On its testeross ear there was one kernel with a nutant of 1

‘

Among the other kernels, 119 were pale colored and 133 were varierated,
Plant 6895B-2 had one Spm element anb it was linked with Pr in
chremosome 5, Among the kernels on the testcross ear it produced the
following phenotynes apreared: Tl pale colored, Pry: 154 pale colo:ed, pr :
131 variegated, Pr : 71 variegated pr.

Plant 6895B-3 had one Som element and it was linked with wx, Among
the kernels on the test cross ear it produced the following phenotvres
appesred: 91 pale colored, Wx : 18 vale colored, wx : 117 variegated,
Wx : 75 variegated wx.

Moat. Oe Report

Aivaough’ t ‘ only 5 plants in the
WA S23 Oana o > hw

progeny of plant 6666C-7 7 the difference’ in t& constitution and location

Done, hain “tomo ale
of=rt in-esch clent was steikine. Both testcross ears produced by the

 

Dabent plant were partially st.rile in that some ovules did not »vroduce
kernels and others produced kernels that were abortive in their develooment.

Also, cn both ears, the percentage of kernels having Spm was Low. On

Wav,

none of the ears of the 5 progeny plants was ste srility expressed | and ‘a

noticable reduction in proportion of kernels having Spm was exhibited only

dap Ove eeny

by plant 6895B-3 and this did not evnroach that given by tne ears of the
A

parent slant. Obvicusly, there must have seen eith>r a burst of

part
transvositi ns of Spm in th#® plant most of which occurred late in
x p a? \

development, @ a succession of such transpositions leading to the formation
a
La
sO

of gametes in which Spm occunrvied various different location in the
VA Om au, OF SUE CARA
chromosome com: Zenente

Prog Tok 13° pega pn

~ “Progeny tests were conducted witn plants derived from the varierated

 

- =
Tot i
ate ead PERG.

kernels on the e rs produced by plantg 6895A-1, in which Som was closely

cullut V2b\
linked with *, and by nlant 6895B-3 in which Spm was linked with Wx,
har Le Cia AM than Uo aa
(Hite megand—to, Fhe subsecuent behavior of “nm, these-pyreceny tests
Wty . UMA
gave strikinsly different ,resudes. The “pm in plant 6895A-1 neued+e—be
Zo as un elt, in eburene 9
relatively stable in location whereas that in -lant 6895B-3 underwent
a” YA A

many subsequent tr nspositicns,. It may be recalled that the Spm in

7 THe Spe ay AD) us fae
olant 6666C-7 was derived fro om, that in plant 6629A-1 anetilel the Spm in

ate pore
LAM,
all subsecuent progeny may be considered to be—-destved from tha?Spm, ae titks

UF Adem srwetint Thad Wau poettion % Span Uy 0 weer tocalon
’ 66ROA—Lpmeit .. Bre- ~follernine—trens-esition of ++ to
Meu, rbauet there iu ve eubogaoat hupacier Cunel We olga 77 hy wtf woah
a~neulocation canditter and 6,u th resect te—supsecrent
Td Quel Pogues «4 eewingune 29 Rulk rg cout Town proebon May Wty adr 0. Artolp DALE
trenspesitiong thatweeurs- The control of this may reside in the Spm

ar DR Ceeqaiue a
element itself in that some change may occur to it Gunning the transpesiticn
Cn Who SU Wend, ms |
process, Heveven, th 16§ control may reflect the particular orranization

arb,

f the renetic materials at the site it oceuppies at any one time,
A

 

 

Evidence for this lattsr interpretation was obtained from sme of the
Ds -~ Ac system. Two independently occurring cases of insertion of Ds just

to the left of 8h, in chromcsome 9 resulted in fixation of Ds at this
location, Althoveh many thousands of kernels were examined in any one of
which an Altered location of Ds could have been detected, not one case of
this was found, If there had been only one discovered case of insertion
of Ds at this location, just tc the left of Sys nothing could bevecneluded
about the factors that are resvonsible for its Stability of locaticn,
There were, however, two such cases following which Ds beh ved in exactly
the same manner, and this suggests that the site in the chremosocme where
a convrolling element resides is an imoortant factor in the control of
an

subsequent transpositicns of such/elematy., be it Ds, Ac, Som, or any
other of this species,

We may now return to give the evidence of the differ nce in behavior

, tt at hy
wat

of Spm in plant 6895A-1 when compared that in plant  6895B-3. As stcted
A

above, in plant 6895A-1, the Spm element was located close tc Y in
chro. aosome 9 as the kernel tynesbn its testeross ear indiestedf part ry
table be Seventeen plants were grown from the variegated Y class of
kernels on this ear in the summer of 1956 under cultire number 7260.
All of the -lants wore variegated, She silks of eech fertile ear of every
a plant in homozygous for
plent received pollen fron/the tester stock which was/a,” 1 state 5718),

Ys pr, and wx and in which no Spm was >resent. “he kernel trres on the

ars thesqolants ‘roduced are given in parts II end III of table 3,
Li

gud
In 1h. plants the location of Spm was the same as in the pva>ent plantg in

Dn ALUM Vy Vip val og Kea: mY so OF WE 2951 Leeks Podete ed ) Paki, who 43
all tested parts of each plants The—kernel tunes apsesring—on—eech—of—the

ears these lh plants produced -is--siven in part it ef this-teble, Only
U.S percent of the kernels on these ears were in the "recombinant" clesses,.

a) oll

The patio of kernel tyres on tee ears of three vlants differed from this

“\ A
Ww Vo rut
in some manner, and these awe givem in part III of table 3. In plant
wh Locator w Uy Wore, brerul Auhont a thy YBAL ( alid
7260-2, Llinkece of Spm wktit VY was empressed by the metbeof keel tunes

wh
oR mar Uy \ Wied Ue haly thas Wd y vif ft YA iy ay .
appecming on the car of the main stalk although the ratio of the pale colore

.

- { . , ng.
lors yp Aalid wn Os Ue poly Bite, atuie owt te CO
to the variegated class was somewhat—-hapher than on the ears vroduced by
A 7 '
a Ap etd Ge ater ¢ Laveen lod ly This
the sister plants, entered in part II, suggest tae otter that the Spm in it

    

Q - “ He y eg Cpr
Wan "Updos ull abooptine: gis aad Has Sp
wos—undergeing more transvositions }k i oe than in the sist r
t .s ° A
plants. On the ear produced by the tiller of this rlant, no evidence was

given of linkage of the one Spm in it with Y, On the ear obtained from

plant 7260-16, a small sector was present in which all of the kernels were
novnpua lr,

pale colored. On the west of this eap, however, the ratio of kernel

tyves was the same as that on ears of the sister plants in part II of table

36 The ear produced by plant 7260-17 was partially sterile and from

the ratio of kernel t:pes on this ear, it was clesr that some abnormality in

the Pom carrying + chromosome was responsible for this sterility. The

nature of tuis abnormality is not known,
If no transposion of Spm occurs during development of the sporogenous

(u-
or spore celis in plant having one Spm, then half of the gametes it
A

Rune

NK

produces would one {Som and half would have no Spm, As a consecuence,
A

half of the kerntes on the testeross ear it produces would be varierated

i“,

and half would be pale colored. However, such treanspnostions do oce’ and
and often this results in the apoesrance of two Spm elements in one
nucleus of a sporogenous or gemetonhytic cell and no Spm in its sister
nucleus. Because of this, the proportion of cells with no Spm in the

Sporogenous or gametophytic cells will depend uron the frequency of

nw

occurrence of trenspositions ,that—hed_ccourpred-_enrlier-in cevelupment.

thus, the proportion of kernels on testeross ears that are pale colored
aude
will inersase as the rate of tats transposition increases, aad fnany peogeny

pout-acl an nar bdo bat io acrpouniteo feu

tais interpretation ef deviation

 
 

tests have i

7 oo Wl & “ . thank of Ga eapoans

from the one pale-colored to one varies ted kernel om testcross ears of

A

Wet initially

plants/hav ig one Spm in their naclei, Therefore, whenever the ratio of

pale colored kernels to variesated kernels deviates from the 1:1 in

A

favor of the pale class on a testcross ear of a slant having one Som

wd \e eur perkoy ty Le haf Ree pled

the cause for this is-wseuebby transnosition of Som in a number of cells
/

te Vand ho °
N 4
late in develonxent of sporogcnous or gametonhytic tissues, For this
, A A A

wate
conclusion to eapety, the pale colored kernels on such ears must be
scattcred over the esr an not be clustered, it is obvious that the

Lode, wn clube pcurt tyrone oo

latter arises from an > event in a single cell) Rrrects
a >

 

Cet.
tw < > a VS ‘uted waLep, e wat oper tly, sil
et ther transvositicn of Spm or @iye inactivation On some e°rs,

ady. » A
° yryourset petty 1 patio, verre

rhalance in t& ratio of vale to varierated kernels, reseits—not—frer-

 

Usuetis, it is nossible to x $ boatween the two types of
_ tly w ia Local ov va ubwa.

change in Spm ‘that are responsible for the unequal ratio of the two
t

Hour Vb w trouubly oao

classes of kernels on an ear, Weyvthis is se will be indicated in the
of this revort
section/desling with inactivation of Spm,

The tesss conducted with the vroseny of plant 6895A-1, described
above, indicated that the Sym in it and in the majority of its promeny
did not chance its location during e°rly develorment with anv marked

Also,
degree of fr ccuency fas the ratios of pale to varlesested kernels on the
testcross ears entered in port II of table 13 indicate, not many
transvositionsn of it were occurring late in development of the sp6rorenous
cells, Sowever, the Spm in the sister »lant, 6895B-3, underwent many
trenspositions and the evidence of this will now be given,
Panay EAP ei dicuche
. The Spm in »lant 6895B-3 was located in its Wx beering chrovosone 9,

as the kernel types on its testeross ear indicated (see line 1, teble li).

It may be noted that the ratio of pale cclred to variesated kernels
144

on this ear (275 pale : 192 variegated) deviated greatly in favor of the
pale class. That some of this was due to transposition of Spm was
suggested by the Spm constitution in plants derived from the variegated,

Wx class of kernels on this ear. The seventeen examined progeny plants
were grown under culture number 7261 in the summer of 1956. Sixteen of
them were variegated and one was totally pale pigmented. On the testcross
ear produced by this latter palnt, none of the kernels gave evidence of

the presence of Spm. Twenty-nine testcross ears were obtained from the

16 variegated plant in this culture. In only 5 of them was “pm linked with
Wx and then not in all parts of each plant. Many changes, both in location
of Spm and in its action must h-ave been occurring in these plants as the
kernel types on the ears they produced indicate, table 44, Also, chromo-

w Rowe Coram
somal abnormalities may have been produced when this ocourredas the

v
deficiency in the Wx class of kernels on the tiller ear of plant 7261-5
suggests. Also, on some ears x*hexprapertxenxpg the pale class of kermels
greatly outnumbered xhxkufihex the variegated class. In one plant,
bearing
7261-10, an Spm element appeared to be present in the wx/chromosome as well
as in the homologue with Wx but at a different location in the chromosome.

In plant 7861-12, the Spm in it was fully active in the tiller but in the

arnrel
main stalk, it was inactive in a number of kernels peedreed—be-—beth
145

aoe

on the Earxekx the first and the second ear. Among the kernels on the
three ears ofplant 7261-6 in which Spm was present, a few appeared in which

the Spm in them was only weakly active (see section dealing with the Spm-w

Yeo"

state of Spm). , The majority of these kernels were in the wx class.

It is obvious that inpompurison with the beh:vior of Spm in the
progeny tests so far outlined, the—Spm in plant 6895B-3 was behaving in
an unusually aberrant manner, not only because of the frequent transposition
of ih that were occurring, but also because of changes in its action that

ainn eee? &,
took place, and‘the possible effect it had in plant 7861-6 in introducing
“A

)
a modified type of Spm action in the non-Spm carrying homologue with wx.
Unfortunately, further progeny tests were not contunted with any one of
these plants. Thus, no more was learned of the subse;uent behavior of
this Spm that originally was present in plant 6629A-2 but had been greatly
altered in its mode of behavior in the second generation plant, 6895B-3

and,in some of ie progeny, in turn,
A
VWL6

At this voint in the discussion of transvosition of Spm we will pause
to review the evidence of this that has been given so far, Por this
purpose, we will cm/fine the discussion to those that occur in plants
having only 1 5pm element in them, In the first plsce, the aposarance of

In

these plants may be considcred, /those isolates of Spm that undergo
early occurring tiansposition during development, the effeet of this is
made visible in the apocarance of the plant itself for they have large

» produecet
sectors in them that exhibit the pale vigmented phenoty~e that a»ise when

; abou . . ;

me Spm is ¢ t. If such a sector extends into that part of a vilant
that produces an ear, the presence of it may be evident enongethe kernels
on the ear following the test cross conducted with it. If the wells
that give rise to the ear are derived only from those within the vale
sector, .fhéh all of the kernels on the testcross ear will be pale pisemented,
If, however, only some of the cells within the pale sector cont»ibute to
the ear, then a clearly defined sector will arve r on the testcross ear
in wich all of the kernels will be pale viemented. fircain, if a pale
sector extends into the tassel, pollen gains collected from anthers

{urd flown
within the sector do not contain Som in them and \when used to make a
A
a m=]

tost>cross, all of the/kc~nels on the resulting ear are pale pienented,

 

fer—tbhes_do_not_heve—Serr-tn them, If pollen #® collected from the
147

the variegated parts of the same tassel is used in making a cross, then
both the pale colored and the variwgated kernels appear on the testcross
ear. Tests of this type were conduct:d and they give the types of

resuit just described. Thus, the appenrancebf uniformly pale pigmented
sectors in variegated plants, the number of them that appear in any

one plant and the7/y relative sizes of them,reveal the time of occurrence c
of transposition of Spm,yduring development as well as the frequency
of—cocuszence of this at any one time. However, inactivations of

WA AME ain YD GO peat
Spm may produce similar patterns of pale pigmented sectors, ii
A

wsriegated—pients but often it is possible to recognize the pale
pigmented sectors that arise from inactivation, as will be indicated
later.
Early occurring transposition may also be detected by the

difference in number of Sm elements, or in the location of an Spm
element, in different parts of the same plant, aed Wetailed evidence of
this was given in the discussion of the behavior of Spm in plant 6872A-12
and its progeny, thit w@ke examined in several successive generations
(see pages. and tables 36 to 42). A high frequency of late occurring

Rye 4 Aron abe ws
transpositions of Spm may be detected by several meuns: the appesrence
eo the plant, the ratio of pale to variegated kernels on its testcross
ears, and the number and distribution of Spm in its progeny pants.
Theplant exhibits a pattern of variegation composed only of small
streaks eee in a non-pigmented background with States 571L9A-1
and 5718 of an inst were extensively used in studies of transposition
of Spm. These are produced either by mutation to or towurds Ay type
action or by loss of Spm from some cells late in ‘development. No large
pale pigmented sectors usually appear in them. Also, the number and
location of Spm is constant in various parts of a single plant. However,

on testcross ears of these plants, the ratio of pale to variegated

kernels deviates markedly in favor of the pale class. In the progeny
148

on nue £6.
derived from the variegated class of kernels, many plant may have
A

either two or more Spm elements in them or one Spm at a new location
in the chromosome pomplement in comparison to the location it occuppied
iti the parent plant.

If the Spm in a plant does not undergo frequent transpositinn

othe pout

early in development nor during development of the sporogenous or spore

A " é
tin nro men, be detotel. Aunty Wat gr douse
cells, fhe appeurance of the plant is-qndte.unifornm. With states

5719A-1 and 5718 of a,™, small pigmented streaks produced by mutation

to or towards A, type action appesr in a non-pigmented background. On

Areunbio. |

the testcross ears of these plants, the ratio of pale to variegated
“A
kernels approaches 1 : 1, the deviation in favor of thepale class being

small. Also, in the progeny of these plants, few cases of transposition
M 4rwe WO ,
of Spm are detected. In-some—-eases, the rate of transposition of Spm
mens, Upon Tobe
ina plant is low, when this is judged not only from the appearance of
~pabh .

the plant but also from the number of cases of transposition of it enecun
Gormul> OW hy prodenset We plo,
encountered in progeny plants derived trom, +s testcross ear. However,
. . ‘4
daw Lilly towlututigy 200
when judged from fumetéion o£ its pollen grains) the rate of transposition

7
RABampicr wun  —s- Uae
may be much greater,{ and—suek—eases keve—been found. The difference

Yap

in proportion of female gametes that carry a transpos#d Spm element
A

to male gahewes having such may reflect the delay in time of occurrence
149

of transposition of Spm that is characteristic of the particular Spm

Pour wd plot. ey bel :
understudy, the cells in the tassel aris#{g~ lather than those in the
4

ear.
_

Progeny test 17, figure 2

 

Examples of transposition of Spm, previously discussed, and those
that will be discussed in the future, should be reviewed keeping in
mind the conditions associated with it that have been outlined in the
preceeding paragraphs. In continuing examination of transposition

at another site
of Spm, the progeny of a plant having Spm/in chromosome 6 will be
discussed. The presence of Spm at this site was first detected prow
the ratio of kernel types on an ear of a plant (6704B-4, see table 18)

m-1

carrying state 5996-4 ay and Sh, in one chromosome 3 and a, and Sh

L 2

in its homologue:;when an ear of this plant had been used in a cross

with the tester plant, 6678, whose constitution is given in table 19.

The phenotypes of the kernels on the resulting ear indicated that one

Spm was present in the ear-bearing plant and that it was carried in its
wnt "

bearing chromosome 6. This is shown in line 1 of table 45.

To investigate further the behavior of this Spm, variegated kernels

in the Y class were selected from this ear and sown in the summer

of 1955 under culture number 6885. In culture 6885A, 15 plants were

derived from kernels that had received state 5996~4 am from the female
150

pzrent and in 6885B, the yallnte had received ay from the female parent
and state 5719A-1 from the male parent. All 24 plants were variegated.
Testcross ears were obtained from 22 of these 24 plants. In 21 of then,
1 Spm was present and it was linked with Y in 20pf these plants, as shown
in table 45, In one of these 20 plants, plant B-8, there was a marked
deficiency in the y bearing class of kernels but the reason for this was
not determined. It was obvious, nevertheless, that the Spm in it was
carried in the Y bearing chromosome 6.-\ Excepting pbant B-8, the ratio of
the pale class to the variegated class of kernels on the testcross ears
of these plants indicated that the Spm in them did not undergo

frequent transposition late in development. An one plant, B-8, the
Single Spm element in it was not linked with Y. In the remaining plant,,

B-9, table 45, two Spm elements were present and one of them was likked

with Y.