~o29—

That an inverted order is present is again supported by the types
of crossover chromatids that could appear if type (1) organization were
present but would not appear if tyne (2) organization had been present
in plant 4306 or in plants 4628D-10 and Dell (table 8), Figure 2
illustrates the tynes of crossover chromatid that could be anticipated
from cenic orders (1) and (2) above, Homologous synapsis of the normal
chromosome 9 with the distal seguent would give phenotynically similar
crossover chromatids in the two cases, * Romologous synansis of the
normal chromosome 9 with the proximal segment, if order (1) were
present, could give rise to crossover chromatids havins the constitu-
tions shown in 3 of figure 2, The crossover c.romatids that should
arise from this association have not appeared. If order (2) were
correct, such crossover chromatids would not appear, From this
negative evidence, order (2) is again indioated,

It 1s possible, now, to reconstruct the events thit zave rise to
this Duplication chromosome 9 with a transposed %s locus, Three
assumptions regarding these events are recuired., (1) «a Ds mutation
occurred at its usual time--late in the development of the sporonhytic
tissues--in a cell of plant 4108C-1, The chromosome in which this Ds
mutation occurred was normal in morphology and carried I Sh Bz dx and Ds
in its standard location, The Ds mutation resulted in breakage of the
two sister chromatids at the position of the Ds locus in each chromatid.
Evidence that a Da mutation brings about breaks in sister chromatids at
the locus of Ds is well established, This assumption is therefore
legitimate, (2) The Ds mutation not only caused breaks to occur at the
position of the Ds locus but resulted in the release of a submicroscople
chromatin segment that carries a Da locus, This released segment
carrying Ds has unsaturated broken ends. It could be lost from the

chromosome complement if fusion with some other broken ends did not
~30-

occur. Loss of the Ds locus as a consequence of Ds mutations has been
considered in detail elsewhere (see report on ceml mutations, January,
1949), The manner of this loss may be suggested from cases such as the
one being described, (3) At the same time that the events described
in (1) and (2) occurred, a spontancous chromogome break ocourred just to
the right of the I locus in this chromosome, Both sister chromatids
were broken at the same locus, “vidence for frequent spontaneous
breaks in aaize is sood (MoClintock, unpublished), This assumption,
therefore, is legitimately taken, ‘hese three events would cive a
series of broken ends as shown in a, figure 3, “usion of broken
ends could readily occur to give rise to the configuration shown
in B, figure 3, “he resulting chromatids are diasrammed in C, figure
5. « Dunlication chromosome 9, with an inverted order of genes in the
proximal duplicated segment and having a transposed Ds locus just
to the right of the I locus is now formed,

On the basis of the depicted rode of origin of the Duplication
chromosome 9, it must be assumed that the two Ds loci are daughter
DS locl derived from reduplication of a mother 3s locus, The -utae-
tional behavior of the two 2s loci in this chromosome are not alike.
More dicentric chromatid-forming -utations oceur at Det than at
De®, The states of the two Ds loci definitely differ from one
another, This is particularly upoarent when these two loci are
senarated by crossing over and the crossover chromatids isolated,
Vhen, the ~utational behavior of Dsl may be directly compared with that
of Os", Either a change in state occurred in one or both of the Des
loci during one of the events that gave rise to the duplication and
the transposition; or 2 chanze in state in one or both Ds loct took
place subsequent to this event, There is no evidence for any vesition

effect associated with the altered genic associations of the to Ds loci,
Figure 3
A.

Position of chromosome breaks

 

B.

Fusion of broken ends

 
Figure 3 oO,

Resulting chromatids

 

IW shBy We Wa RQ ch Co
T .
ne fp

 
aot le

Changes in state of these two separated Ds loci are occurring indepen-
dently of their positions as no few of the variegated kernels have
shown.

Again, it should be emphasized that the transposition of the Ds
locus has not introduced any visible alteration in the appearance of the
chromosome in the region of the transposition. Neither has its
insertion affected the crossing over in the I to Sh region, To
refresh this evidence, a summary of this crossing over in the crosses
of clants in sub-cultures 4628 7, G and 'l are given in table 20,

These observed crossover percentazcs are similar to those observed when
no Ds locus is present, The inecrted segment carrying Ds must be very
ninute--obviously submicroscopic in size,

The analysis of this case of transposition of Ds has indicated the
method for selecting those relatively rare kernels with newly arising
transposed Ds loci, In the crosses of I Sh Bz Vx Dseestandard to
C sh ba wx ds ao plants, the kernels with aberrant variegation of cuite
svecific tynes may be selected, It is possible, by this method, to
detect those chromosomes having Ds inserted to the left of I,
between I and Bz and between 5z and Wx. aA number of such kernels have
been selected and an analysis of the transposition of th Ds locus is
being conducted, Evidence from these other cases should be well
advanced by the time the greenhouse crop is collected and certeinly by

the time the summer crop is harvested,
Table 20

Summary of crossing over between I and 3h in plants 4626F-1, 4628G-1,
G2 and Ge3, and vlant 4628H-}

Normal chromosome 9 I Dal gh

 

Normal chromosome 9 C ds sh

 

 

Table reference “ot Kernels arorscover cron eco ae
chromatids
Table 9, 4628F~<] 564 28 4.9
Table ll-a, 4628 1461 85 5.5
Table ll-b, 4628b 1243 49 349
Table 12, 4626H-1 525 19 3.6

 

Totals 3793 181 4.7

 
-~ 32 - transpOsed Ds 4628
ps Case I Duplication rode

Appendices to: Fane} dus
Transposition of the Ds locus, April, 1949. Vas?

In the previous account the Case I transposition of the Ds locus,
april,1949. the origin and behavior of this case of transposition was
analysed in considerable detail. Continued examination of this case
has resulted in corfirmation of the conclusions given in the earlier
report. In this supplement, the confirmatory evidence will be given
in the form of appendices. The table numbering will follow sequentially
from the previous resort.

Appendix 1

In the cross given in table 7-c, an Ac ac, C sh bz wx ds female
plant was crossed by plant 4628C-9. This latter plant was homozygous
for the duplication chromosome 9. Both chromosomes carried
I Dst Sh Bz wx Wx Bg Sh Ds*, The plant had one Ac locus. A number of
kernels appeared on the ear that showed only a few specks of © color
(column 1, table 7-c). It could be anticipated that these kernels had
3 Ac loci in their endosperm cells, two contributed by the female parent
and one by the male parent. If the Ac loci in both plants were located
in allelic positions, the plants arising from these kernels should be
Ac Ac. Some of these lightly speckled kernels were selected from
the cross of 4462€-11 x 4628C0-9 (Table 7-C) and plants grown from
them in the summer of 1949 under culture number 4876A. these plants
were crossed to: (1) C sh bz wx, ds ac plants (Tables 2l-a and 21-b),
(2) by C sh bz wx, ds ac plants (Table 22), and (3) to ¢ sh Bz wx,
ds ac plants (table 2l-c).

In cross (1) above, the types of male gametes, with respect to

chromosome 9 morphology and genic constitution, should be the same as

those given in the supplement to Table 8. It was hoped, however,

that two allelic Ac loci would be present in the tested plants so that

Bel
- 33 -

a more direct analysis of the chromosome and genic constitutions of
the resuiting progeny would be available. The four tested plants
in Table 21-a had two Ac loci. Unfortunately, however, these two loci
did not occupy allelic positions, as the results given in this table
indicate. The classes of kernels and their frequencies are those
expected if these four tested plants had two non-linked, non-allelic
Ac loci. This is shown in the supplement to Table 2l-—a. It must
be concluded, therefore, that the Ac locus in the two parent plants
occuppied different positions in the chromosomal complement. In
all other respects, however, the results are the same as those
given by plants having the same chromosome and genic organizations
that were tested in the previous season, Table 8. Therefore, no
further description or analysis is required.

In one plant of culture 4876A, the Ac constitution of the
main stalk and the tiller differed. This is shown by the
frequencies of kernel types obtained when pollen from the main
stalk and pollen from the tiller were used in crosses to C sh bz wx,
ds ac plants, Table 21-b. The ratios of kernel types obtained
when pollen of the main stalk was used indicate that only ong Ac
locus was present. The pollen from the tiller gave ratios of
kernel ty;es that indicate the presence of two non-linked, non-
allelic Ac loci. It cannot be decided from these tests whether or
not the tiller gained an Ac locus or whether or not the main stalk
lost an Ac locus. Hither event could account for the observed
difference in the two parts of the plant.

Two of the plants entered in Table 2l-a were crossed to
ec sh Bz wx, ds ac plants. The types of kernels appearing on the
resulting ears are given in Table 2l-c. As the supplement to

Table 2l-c indicates, the types of kernels and the ratios
- 34 =

observed are those expected from the stated constitution of these

plants.
In Table 7-c, one aberrant kernel was recorded. This kernel
had the phenotype C Sh Bz Wx and was non-variegated. Such a kernel

was not expected to appear following the cross given in Table 7-c.

A plant was grown from this kernel. It was crossed to ac sh Bz wx,
ds ac plant. There were 345 kernels on the resulting ear. 51 were

C Sh Wx, non-variegated; 2 were C sh Wx, non-variegated and 292 were

C sh wx, non-viriegated. When the plant was crossed to a C sh be wx,
ds ac plant, the resulting ear showed 27 C Sh Bz Wx non-vriegated
kernels, 23 C Bz + C bz, Sh, Wxewx (bz areas wx) kernels, 2 C sh bz Wx
non-v:riegated kernels and 116 C sh bz wx kernels. The plant was
likewise self-polliniuted. The resulting ear showed 229 C Sh Bz Wx

(a number were variegated) one C sh bz Wx and 156 C sh bz wx kernels.
If the tested plant had the constitution Duplication C sh bz Wx Wx

Bz Sh Ds/C sh bz wx, ac ac, just such ratios following the given
cross would be obtained (see Tables 15-b, 15-c and Tables

It is suspected that contamination was responsible for the appearznce
of the aberrant kernel in Table 7-c,or that the pollen grain that

gave rise to this kernel had a deficiency in the distal segment that
indluded: the I,Ds, Sh,and Bz loci. Only further tests could
distinguish between these two possibilities.

In the April 1949 report, no evidence was presented for the
trinsmission of the duplication chromosome through the egg parent.
Plants heterozygous for a normal and a duplication chromosome 9
give reduced transmission frequencies of the du: lication chromosome
through the pollen. The ratios of tee C Sh Bz Wx Kernels to tke
C sh bz Wx and C sh bz wx kernels in the crosses of C sh bz wx by

yt 4
Duplication C sh bz Wx Wx Bz Sh Ds/normal chromosome 9, C sh bz wx
- 35 -

indicate the transmission frequencies through the pollen of the

dup.ication chromosome 9. Compilation of the data from Tables
give a ratio of

Duplication chromosomes 9 to normal chromosomes 9. such a

reduction in transmission of the duplicated chromosome is likewise

1 sh Bz wx Wx Bz Sh Ds“/

evident when plants of the constitution I Ds

C sh bz wx are crossed to C sh bz wx. Because the crossing-over

between the distal Wx locus and the proximal segment is low, the

frequency of the Wx to we class gives the approximate frequencies

of transmission of the duplication and the normal chromosome. The

combined data from Tables 8, 2l-a, 21-b and 2l-c show 1694 Wx to

3331 wx kernels. In the reciprocal cross, no such reduction in

trinsmission of the duplication chromosome is expeeted. Four of

the plants entered in Table 21 were crossed reciprocally. The

results of these reciprocal crosses are given in Table 22,

Because of the presence of 4 Ac loci in the endosperms of many

of the kernels, it was not possible to make an accurate classification

for the presence or absence of Ac in all the kernels. In the table

a significant reduction in the Wx class is evident. This is

probably not related to a reduction in transmission of the duplication

chromosome, Rather, it is related to Ds mutations occurring

before meiosis that produced non-female transmissible deficiencies,
Data given in Tables 21 and 22 show that crossing-over

between the normal chromosome and the distal duplicated segment in the

Duplication chromosome 9 is relatively little affected by the

presence of the duplication. This would suggest that synapsis is

not seriously disturbed by the presence of the duplication; otherwise,

a considerable reduction in crossimg-over between I and Wx would be

evident.
-~ 36 -

Appendix 2

In the summer of 1948, plant 4628K-1 (Tables 14-a and 14+b)
having the constitution Dup. C sh bz Wx Wx Bz Sh Ds/C sh bz wx,
Ac/Ac, was crossed by plant 4628L-1 (Tables 16-a and 16-b) with
the constitution Dup. C Sh Bz Wx wx Bz Sh Ds/C sh bz wx, Ac Ac.
it was hoped that some of the plants arising from the C Sh Bz Wx

class of kernels on the resulting ear would be homozygous for the

duplication and for Ac. The ear was small and only a few kernels
of the desired type were available for testing. Six of these kernels

were planted in the summer of 1949 under culture number 4848 but only
4 of them germinated. The constitution of three of these plants
were exactly like the female parent plant (4628K-l1, Table 14) as
the results of reciprocal crosses with C sh bz wx, ds ac plants have
shown, Tables 23, 24, and 25,

One of the plants in culture 4898 (4898-2) had the constitution
Dup. C sh bz Wx Wx Bz Sh Ds/C Sh bz wx, Ac Ac. The duplication
chromosome must have been contributed by the female parent plant
whereas the normal chromosome with C Sh bz wx arose from a crossover
in region 1 of the male parent plant (see supplement to fable 1l6~a).
Reciprocal crosses of this plant with C sh bz wx, ds ac plants are
given in Tables 26-a and 26—b. The cross of this plant to a
ec sh Bz wx, ds ac plant gave the kernel types listed in Table 26-c.
Crossing-over between Sh and wx in this plant was very high in the
microsporocytes but a much lower frequency of recovered crossover
chromatids crime from the megasporocytes. such high rates of crossing
over in this segment of chromosome 9 have been encountered when two
normal chromosomes have been present. A reduced amount of
crossing-over in the megasporocytes as compzred with the microsporocytes

has likewise been observed in numerous tests.
-~ 37 -

Appendix 3.

In the crosses of C sh bz wx, ds ac plants by Ac ac plants

1 Sh Bz Wx Wx Bz Sh Ds*

having the Duplication chromosome 9 with I Ds
and a normal chromosome 9 with C sh bz wx, a number of distinctive
kernel types appeared (Table 8). The projected constitutiow of
these kernels are given in the supplement to Table 8. In order to
determine whether the projected constitutions were correct, some of
the kernels from the cross-over classes were selected from two of

the crosses, 4462C0-8 x 4628D-11, and 4363-17 x 4628D-11 (Table 8) and
grown in the summer of 1949 under culture numbers 4877 and 4878,
respectively. Two plants arising undexrxgukturexnumkers from the

I4+C BzsC bz, Shesh, wx kernels (48774), four plants arising from the
C BzsC bz, Shesh, Wxewx kernels (4877C) and the plants arising from
two C Sh bz wx kernels (4877E) in cross 4462C-8 x 4628D-11 were

tested for their chromosome 9 constitutions. In the cross

4883-17 x 4638 D-11 (Table 8), four plants arising from the C Bz-C bz,
Sh-sh, Wx-wx kernels (4878D)were tested for their chromosome 9
constitutions.

Table 29 gives the ratios of kernel types obtained when the two
plints ariwing from the I BzeC BzyC bz, Shash, wx kernels were crossed
by C sh bz wx, ds ac plants. The results are those anticipated from the
given constitions shown in the heading to this table. The plants
arising from the C Bz-C bz, Sh-sh, Wx-wx kernels should all have the
Duplication chromosome 9 but the genic constitution could be. several
types, as the supplement to Table 8 and Figure 2 illustrate.

Crossing over in regions 1 to 5 would give the following genic

constitutions in the duplication chromosome:
1 Sh Bz Wx wx Bz Sh Ds*

2

Region 1: Dup. © Ds

Region 2: Dup. © 8h Bz Wx Wx Bz Sh Ds
- 48 -

Region 3: Dup. © sh Bz Wx Wx Bz Sh Ds“

Region 4: Dup. C sh bz Wx Wx Bz Sh Ds°

Region 5: Dup. © sh bz wx Wx Bz Sh Ds“
Because crossing-over in region 4 is the highest, the majority
of the C Bz-C bz, Sh-sh, wx-wx kernels in the cross shown in Table 8
should give plants with the constitution: Dup. C sh bz Wx Wx Bz Sh Ds/
C sh bz wx, Ac ac. Of the 8 tested plants arising from such kernels,
were definitely Dup. © sh bz wx Wx Bz Sh Ds/C sh bz wx, Ac:ac
(Table 27, a and b), were Dup. C sh bz wx(or wx)Wx Bz Sh Ds/
C sh bz wx, Ac ac (Table 27-d). the tests of the latter plants were
inadequate for determinging the presence or absence of the distal
Wx locus. One plant, 4878D-1, had the constitution Yup. © sh Bz Wx
Wx Bz Sh Ds/ n-rmal chr. 9 C sh bz wx, Ac ac, as the results of the
cross of this plant by a C sh bz wx, ds ac plant indicate (Table 28).
fhe constitution of the duplication chromosome in this plant resulted
from a crossover in region 3 of the osrent plant.
In cross 4462C-8 x 4628D-11, Table 8, the 2 C Sh Bz wx kernels
could be expected to appear following a double crossover in regions
2 and 4 in the male parent. A normal chromatid carrying C0 Sh Bz wx
wo:ld result from such a double crossover. fhe plants arising from
these two C sh bz wx kernels were cros:ed by C sh bz wx, ds, ac ac
male plants. The resuits of this cross, Table 30, indicate tne
presence of two normal chromosomes 9 in each plant. No evidence of

a Ds locus in the © Sh Bz wx chromosome appeared in either case.
- 39 -

Appendix 4.

Table 14 gives the tyves of kernels a;pearing when a Duplication
C sh bz Wx Wx Bz Sh Ds/ Normal C sh bz wx, Ac Ac plant was crossed to
a C sh bz wx, ds ac plant. With regard to genic constitutions of
chromosomes 9, four types of gametes could be exvected to be
produced by the male parent. These are:

Non~crossover chromatids
(1) Dup. C sh bz Wx Wx Bz Sh Ds

(2) Normal C sh bz wx
Crossover Chromatids

(3) Dup. © sh bz wx Wx Bz Sh Ds

(4) Normal C sh bz Wx

The genic constitution of the chromosomes 9 of seven plants arising
from the C Bz-C bz, Sh-sh, Wx-wx kernels of Table 14-a were tested.

96 to 98 percent of the plants arising from these kernels should have
the constitution Dup. © 5h bz Wx Wx Bz Sh Ds/Normal C sh bz wx, Ac ac.
All seven tested plants had this constitution. Six plants were
crossed by C sh bz wx, ds ac plants, Tables 3l-a. All. plants

were crossed to C sh bz wx, ds ac plants, Table 31-b, One plant

was crossed to ac sh Bz wx, ds ac female plant, Table 3l-c.

Iwo kernels in Table 14-a were classified as possible C Sh bz wx
kernels. Such phenotypes were not expected in this cross. To
determine if Sh was: actually present, plants were grown from these
two kernels and self-pollinated. The self-pollinated ears showed only
C sh bz wx kernels. The Sh classification in Table 14-a is therefore
ervoneous, as anticipated. These two kernels should be moved to the

last column in Table 14-a,
~ 40 -

Appendix 5.

In Table 16-b, which gives the types of kernels appearing from
the crosses of c sh Bz wx, ds ac female plants by a Dup. C Sh Bz Wx
Wx Bz Sh Ds, Ac Ac plant, a single aberrant kernel was observed.
Two Cotrdess Omd SrQURd Sr or dnd Wey ioy Cam eset ay
This kernel was sown in the summer of 1949 and the plant arising from
the kernel was crossed to a C sh bz wx, ds ac plant and ac sh Bz wx,
ds ac plant. The tyes of kernels appearing on the two resulting eurs
indicated that this plant had the constitution I Sh Bz wx Ds Ac/
ec sh Bz wx ds ac. This constitution could not have been produced by

plant 4628L-1. The aberrant kernel in Table 16-b, therefore,

represents a pollen contamination and should be removed from this table.

Appendix 6.
In the crosses of C sh bz wx, ds ac plants by Dup. C sh bz Wx

Wx Bz Sh Ds/Normal C sh bz wx plants, Tables i4-a, 15-a and 15-c,

a few C sh bz wx kernels appeared. These were interpreted to arise
from crossovers as indicated in the supplements to these tables.
They should have two normal chromosoues 9. Plants from seven such
kernels were examined cytologicilly and all seven showed two
morphologically normal chromosomes 9. Two of the plants were self-
pollinated, Table 32-a, and two were crossed by C sh bz wx plants,
Table 32-b, and one was crossed to C sh bz wx, Table 32-c. The

expected ratios for Wx and wx were obtained.

Appendix 7.

In the cross of a c sh Bz wx, ds ac female plant by plant
4628L-2 which had the constitution Dup. © sh bz Wx Wx Bg Sh Ds/normal
C sh bz wx, Ac ac, an aberrant kernel appeared. This cross is not
given in the April 1949 report but is similar to that recorded in
Table 17=-b. This exceptional kernel was colorless and showed

Sh-sh, Wx-wx viriegation. A pant was grown from this kernel and
-~ Al -

crossed to a © sh bz wx, ds ac plant, Table 33-a, and by a C sh bz wx,
ds ac plant, Table 33-b. These tests showed that the plant carried a
Duplication chromosome 9 with © sh bz Wx Wx Bz Sh Ds. The phenotypic
appearance of the kernel from which this plant arose may have been
produced following an early spontaneous break that deleted the © locus
and initiated the breakage~fusion-bridge cycle that produced the

Sh-sh, Wx-wx vuriegation.

Appendix 8.

a ee

me bef Le

in order to obtiinaplants hiving a chromosome 9 with I Ds Sh Bz WX,

bendy: 3 “tay ‘OAS

‘Ae ac) 1 Bazo B2yC bz, Sh Wx kernels were selected from the ear of a
C Sh bz Wx/e sh bz Wx, ac ac female plant by plant 4628G-2 that was
I Ds Sh Bz wx/C sh bz wx, Ac ac. Two plants arising from such
kernels were crossed to © sh bz wx, ds ac female plants, Table 34.
The supplement to Table 34 indicates the types of kernels that should
appear following crossing-over. Crossing-over in region 3 gave the
desired constitution: I Ds Sh Bz wx. In these kernels, the C Bz
areas were viriegated for C bz and the majority of these latter areas
were WxX-wx viriegated. This is the expected viriegation pattern
that should be produced from dicentric formationas at the Ds locus,
immediately to the right of the I locus, which initiates breakage-
fusion-bridge cycles.

In these crosses, there were 6 C Bz-C bz, Sh-sh, wx kernels.
Such phenotypes could arise from crossovers in region l. It is
possible, however, to obtain such phenot; pes from I Ds Sh Bz wx
chromatids if a Ds event or events occurs early enough to eliminate
the I locus from all of the aleurone cells. This oceurs in a small

fraction of kernels when Ds mutations take place early in developm=nt.

Plants arisi:g from all 6 kernels would need to be tested to determine
-~ 42 .

whether or not arossing-over in region 1 or early loss of I following
Ds mutations were responsible for the appearance of the C Bz-U bz,

Sh-sh, wx phenotype.

Appendix 9.

The position of Ds in this cxse of transposition is definitely
between I and Sh. That it is close to the I locus has been apparent
from various crosses previously described. Calculitions of the
crossing-over between I and Ds (see prge 16) gave a percent ige of
0.74, This value was derived from the frequency of the © Bz-C bz
kernels in the crosses of C sh bz wx, ds ac female x I Ds Sh Bz wx/
C sh bz wx, Ac ac male (Table ll-a).

Tests for the presence of Ds in the C Bg chromosome of plants
arising from C Bzg= C bz kernels of tables lla and 12-b, and the
C-c kernels of table 11-b and 13-c, were conducted by growing plants
from these kernels and testing for the presence of Ds. Twelve

variegated
kernels were selected from,kernels, some from the crosses entered in
Tables ll-a, 12-b and 13-c, and some from crosses not recorded in the
April 1949 report. Two kernels that were doubtful variegutes were

likewise selected and the plants grown from them tested for Ds.

The various selections are given in the accompanying scheme, Scheme l.
(Insert Scheme 1, page 43)

+nformation concerning the origin of the selected kernels, the
nature of the variegation, the projected constitution of the derived
plant, and the culture number of the plant may be seen from the
arrangement in this scheme. The first 10 kernels in the shheme
were certain variegites. Nine germinated to give plants ind all nine
plants were tested for Ds. the last two kernels in the scheme were

uncertain variegates. The kernel that gave rise to plant 4885 had
- 43—

 

 

 

 

 

scheme 1 }
Cross Table ‘Phenotype of selected kernel frojected constitution of plant | 1949 Culture Number
Reference iL iurising from kernel
C sh bz wx, ds ac @ x 1 Ds Sh Bz wx he ae |
C ds sh bz wx .
o” |
4363-14 x 4628G-2 _ ll-a | C Bz-C bz, Sh-sh, wx ‘ 4884
446 2C-1a x 4628G-23 Not in April SCE eee
1949 report | " " " s sh bz wx 4887B
== ny
C sh bz wx 9 : .
= ¢ x I Ds Sh Bz wx , oy 1 C Ds Sh Bz wx
ec Sh bz Wx Suds ch be wx 7f ae ot " C Bz-C bz, Sh-sh, Wx Wds sh be wx 4883B
4358A-2 x 46286-2 : a C De S
| C~ca Sh Wx Ds ©h Bz wx
| eds Sh bz Wx _ 48850

Norm. C sh bz wx I Ds Sh Bz wx

Re. c oh Bz wx $ xX U ds sh bz wx ° ae

 

C Bz-C bz, Sh-sh, wx

 

 

 

 

 

C Ds “h Bz wx

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a “Cds Sh bz wx HEGOC-1, 8900-2
4365-3 x 46 28H-1 12=b 7
| C+e, Sh, wx Norte =o ae 4890D-1, 4890D-2
o— —
c sh Bz wx, ds ac¢ x _I Ds Sh Bz wx Ae ae 1l-b \ ; C Ds Sh Bz wx
Cds 8h bz wx C-c, Sh-sh, wx @ ds sh Bz wx 4886 (no germination)
4347-22 x 46286-2 a
Re. c sh Bz Wx 9 x I Ds Sh Bz wx ac ac 11l-b | ‘ enlenw Norm, GC Ds Sh Bz wx
ds sh bz we gt “Cy MAWSNy NK Re. c ds sh Bz Wx 4882
4353-2 x 4628G-1
C sh bz wx, ds ac@ x I Ds Sh Bz wx Une area only of presence of Ds in
, Sas sh ba we 8¢ 20 7 ti-a | 0 Bz-C bz, Sh-sh; UC Sh Bz wx chromosome 4885
4684-3 x 4628G-3 wX uncertain
i ion
Re. c sh Bz Wxdg I Ds sh b2 wx ,. .. @ _ Possible C-c kernel Presence of Ds in
Norm.C Sy Bz wx Ds $ Cds sh bz wx “© 2¢ & L5-e but not certain 4891

4380A-8 x 4628I-2
Re Re

C sh bz wx chromosome
uncertain.

 
- 44 —

only an area of C Bz - C bz variegation. Tests for Ds were negative.
The variegated area in the kernel from which this plant arose may have
come from a spontaneous breakage in the chrorosome 9 carrying

C Sh Bz wx loci in one cell mid-way in development of the kernel.

The kernel that gave rise to plant 4891 was not certainly variegated.
A few specks that could hive been interpreted to be c in phenotype
appeared in this kernel. These c specks were suspected to be the
result of poor color development. It was thought wise to test for

Ds in the plant arising from this kernel. No Ds wis present in

plant 4891.

The nine plants arising from the ten certain variegated kernels
were tested by crossing to (1) C sh bg wx, ds ac, (2) ec sh Bz wx, ds ac,
and to (3) Rearranged chromosome 9 c sh Wx, ds ac female plants,
Tables 35 to 41.

The types of kernels appearing on the ears when plants 4883B

and C were crossed to C sh bz wx, ds ac plants are given in Table 35.

. vastalh

The presence of Ds to the left of Bz is indicated in the supplement

to Tuble 35. The variegated kernels may be used to obtain the crossover
frequencies between Ds and Bz. This gives a frequency of 5.8 percent
which is the amount expected if Ds were immediately to the right of the
C locus. Plant 4883B was crossed to ec sh Bz wx, ds ac female plunts
giving the kernel types shown in Table 36. A high percent of
crossing-over between Ds and wx is to be expected, giving a chromosome
with C Ds Sh Wx. When Ac is present, such a chromosome will give

C-c variegation in the indicated cross. The c areas should be Wx-wx
variegated because of the formation of dicéntric chromatids just to

the right of the C locus. The presence of Wx-wx variegation was

evident in all of the C-c kernels that carried Wx. The presence of

¥ Moos

i bw

Ds to the right of the © locus was indicated by the absence of
- 45 -—

twin areas with deep color in one area and colorless in its twin area.

Plant 4883C when crossed as a pollen purent to c sh Bz wx, ds ac
plants, gave the kernel phenotypes entered in Table 37. Crossing-over
between Ds and wx, based on the C-c kernels, was 29.4 percent.

The data entered in Tables 35, 36, and 37 are consistent in placing
the Ds locus immediately to the right of the C locus. It may be
concluded, therefore, that the kernel giving rise to plant 4883B

and plant 4883C wexe received a chromosome 9 that was derived from a
crossover between I and Ds that had occurred in the I Ds/C ds pollen
parent plunt (Table ll-a),

The projected constitution of plants 4884, 4887B, 4890C-1 and
4890C-2 was C Ds Sh Bz wx/C sh bz wx, Ac ac. These plunts were
crossed to plants that were c sh Bz wx, ds ac in constitution.

Plants 4884B, 4887B, and 4890C-1 had the expected genic constitution

as shown in Table 38. Plant 4890C-2, however, had the constitution

I Sh Bz wx/C sh bz wx. No Ds locus was evident. Heterofertilization
could account for the discrepancy in kernel and plant phenotypes but

the absence of Ds events in the I Sh chromosome of the slant arising from
this kernel suggests that a Ds event occurred in the division of the
sperm that eliminated Ds from one chromatid (sperm fusing with egg) and
initiated the breakage-fusion-bridge cycle in the sister chromatid

(sperm entering the endosperm nucleus). The data from the three

plants, entered in Table 38, allow the vosition of Ds in these plants

to be calculated. Only the variegated kernels may be used to

calculate the crossover percentage between Ds and Sh. The value
is 4.5 percent. This is the value expected if Ds is very close to
the C locus. +t is concluded that these three plants received a

chromosome 9 derived from a crossover between I and Ds that plved

Ds close to the © locus,
- 46 —

Plants 4890D-1 and D-2 were given the constitutions projected
in Scheme 1 (pzge 43): Normal chromosome 9 with CG Ds Sh Bz wx/
Rearranged chromosome 9 with c sh aed WX, AC ac. The projection for
plant 4882 was normal chromosome g°C Ds “h Bz wx/rearranged chromosae 9
with c Sh Bz wx, Ac ac. If each of these three plaints were crossed
to plants homozygous for c and sh and had no Ac, C toc variegated
kernels should appear AmMaNeXkheXkExNMEXS on the resulting ears.
Because of the presence of the rearranged chromosome 9 in these
three plants, the position of Ds in the homologous normal chromosome 9
could not be determined by crossover techniques. The presence of
a Ds locus in half of the C carrying kernels (those that have Ac)
is evident, however, in the crosses of these plants to plants
that were homozygous c sh Wx, ds ac, Table 39. Plants 4882 and
4890D-1 were crouged to a plant homozygous for ec sh wx, ds ac.
the results of this test are those expecte, Tables 40 and 41,

None of the data in Tables 35 to 41 gives evidence that allows

a determination of the closeness of the Ds locus to the C locus.

Tables 9, lla, 1ll-b, and 12-a, however, do show that this trans.osed
& : eae

t 5
eh oF ok PR

‘Ds is located very close, to the I locus. From these tables, the
estimited crossing-over between I and Ds is approximately 0.5.
the data in Table 34 project nanmmependeiaamiine of approximately 2 percent.
This value is much higher than the calculated values from the data in
any one of the other mentioned tables. However, several of the
six kernels showing a ¥ Bz + C bz phenotype (projected crossovers)

ama an 6E SEAR beeen: mio base hay Rt
in Table 54 may hae test the I aiid te the “consequence of a Ds
event that removed the I locus from one or both sperm nuclei.
*t will be necessary to test the constitutions of the chronosomes 9
in plants szrising from these kernels in order to determine the
reason for the@® phenotypic expression of each. The combined data

- a. ( prow ar?
indicate, however, that Ds lies to the right of 1 Gnd very close to it.
1 2
I Ds Sh Bz Wx Wx Bz Sh Ds

Table 2l-a

 

 

 

 

C sh b2 wx, ds ac 92 x Dup. Ac ac, ac ac o
Norm. cC sh bz wx
4805B-19 S805B 20 | S807-1 4807-8 (4808-25 4805- 27 |4804-10 !
Kernel type x x 'To otals
“8764-1 4876A+1 4876A+8 4876AW3 | 48763~4 4876A-4 4876A-5 |
I Sh Wx 23 37 7 7 33 22 22 151
I BZ - C BZ - C ba, Sh, 4x-wx 111 102 23 28 50 34 82 430
I Sh wx 10 15 "7 6 15 17 28 98
I BZ -C Bz-C bz, Sh wx 21 21 16 21 30 26 60 195
I bz - C bz, Sh wx 4 8 4 1 2 2 22
I sh wx not obv. var. 4 4 4 4°? 6 3 4 29
I bz =-C ba, sh wx 5 5 4 0 9 7 3 35
C Sh Bz Ws not obv, var. 15 13 4 7 20 9 13 81
C BZ = C bz, Sh, Wx-wx 26 37 4 14 17 15 19 132
C sh bz wx 201 149 60 76 158 129 254 1027
Odds 1c Sh Bz wx oO O 1c¢C Sh B21C Sh 1¢ Sh Bz 2C sh 6
wx Bz wx wx ba Wx
(var.?)
Totals: 421 391 133 165 341 265 488 2204

 

146 We: 140%my
Supplement to table 2l-ea
5

' oa 3) 64

—

 

C ds Sh bz wx |

Non-crossovers:

3
Dup. I Ds Sh Bz Wx Wx Bz Sh Ds
Sl
Norm. C ds sh bz wx Ac & ac
Region 1
Norm, I ds sh bz wx Ac & ac
_o
Dup. C Ds Sh Bz Wx Wx Bz Sh Ds
~i1
Region 2
3
Norm. I Ds sh bz wx i
1
28
Dup. C ds Sh Bz Wx Wx Bz Sh Ds@
1
Region 3
3
Norm. I Ds Sh bz wx
1
a)
Dup. C ds sh Bz Wx Wx Bz Sh Ds
Oy
Region 4
3
Norm. I Ds Sh Bz wx ~
1
8
Dup. C ds sh bz Wx Wx Sh Bz Ds
“1

Pen i ni eet rte a cnet ee

Ac

ac

Ac

ac

Ae
ac
Ac

ac

Ac
ac
Ac

ac

Ac
ac
Ae

ac

a "
Qa aA HH H Qa awn H

"
Qa Q HH He

2

Ds Sh Bz Wx . Wx Bz Sh Ds"

- © Ba - C bz Sh Wxewx = 4530

(with reg. 4 + doubles)

Sh Wx *" " " = 151

sh bz wx = 1027

sh wx

BZ = C bz Sh Wx-wx (bz areas

Wx-wx or wx)

Sh Bz Wx

bz - C bz sh wx = 35

sh wx

Bz - C bz Wx Wx-wx (bz areas
wx)

Sh Bz Wx

bz - C bz Sh wx = 22

Sh wx

Bz - C bz Sh Wx-wx (bz areas
wx }

Sh Bz Wx

BZ - C BZ - C bz Sh wx = 195

Sh wx

Bz - C bz Sh Wx-wx (bz areas
wx)

Sh Bz Wx
Supplement to table

2Zl-a (continued )

 

Region 5
_. 3 Ac = I Bz - C Bz Sh Wx-wx
Norm I Ds Sh BZ Wx =
~~~ Jo ae = I Sh Wx
_%3 Ac = © Bz - C bz Wh Wx-wx (bz areas
Dup. C ds sh bz wx Wx Bz Sh Ds wx)
“J ae = C Sh Bz Wx
Double crossovers
Regions 2 + 3
Norm. C ds Sh Bz wx Ac + ac = C Sh Bz wx = 4
. § Ac = I Bz - C bz Sh Wx-wx
Dup. I Ds sh bz Wx Wx Bz Sh Ds
“7 ac = I Sh Wx
Regions 4 + 5
Norm. C ds sh bz Wx Ac + ac = C sh bz Wx = 2
3 Ac = J Bz - C bz Sh Wx-wx
Dupe I Ds Sh Bz wx Wx Sh Bz Ds
lac = I Sh Wx
Supplement to table 2l-a (continued)

Normal chromatids

Non-cross-over 1027 C sh bz wx

Regions 1 + 2 62 I sh wx = I to Sh

Regions 3 + 4 315 I Sh wx = Sh to Wx

Regions 2 +» 3 = 4 C Sh Bz wx

Regions 4 + 5 2cC sh bz Wx

Totals 1410

% cross-overs region I to Sh = 4.6% (see Table 20 in Report
April, 1949 = 4,74)

% " wt n Sh to Wx =22,48%

Conclusion:
Presence of Duplication does not interfere with the normal

amount of crossing over in the region between I and Wx of the

distal segment.

 

Ratio of 2, 3 and 4 from variegated kernels with I
Region 2 = 33 I bz - C bz sh wx
Region 3 = 221 bz = C bz Sh wx

Region 4 = 195 I Bz - ¢ Bz - C bz Sh wx

Ratios 1.5:1: 9