wy

the breakage-fusion-~bridge evele and the origin of instability at

fene loci,

I, Review of evidence go

a)

Lar presented:

1. Attompted to present evidence of the origin and behavior of instability

at a number of ‘now gene

loci in neaize,

2. Much of this ecnfined to cas2s where Ac- controlled the cenic action,

Th,

this done to keen down the need for too much riemory of individual cases --

a unified theme for the prescntation of cases,

3. “ave show that both
transnosit® ons occur in sone

Ds and Ac are transposible units and th
ti cells at certain times during the develooment

of a tissue, under control of Ac itsolf,

lh, save shown that muta
of the lmown gene ine sse

5. ave shown in these

4
an event involving Ds -- loss of Dg activity conicident with the

ability arises when Ds activ jity a rears at the locus

of cemL and bz=ml.
cas cs thav mutation at the locus is associated with

mutation,

©

6. Have shotm shat chances in state occur at Ds, when at the clocus of

c-ml op bz-ml or at Ds in

otner Locations,

7. tlave indicated the stabilitys of the states of e-ml and the suecession
of states that occur -- one from tee other

8. We lmow that events

at Us and also at Ac can lead to a physical cnuanrge

in the chromatin at the locus because of *? dicentric formas cion, invyersions

duvlica ‘Glons, I ring cnromoson

Lyidence noints

» translocations ete, that have been observed.

to some ecnange that results in a physical gatleration of she

chromatin materials at the locus. wvidence sugreests that transfos*.tions

arise from this nrocess,

9. We lmow that no alterations occur ab the Ds loci, or the loci who:
mutatility is controlled by Ac, if Ac is absent, hutability will occur,
however, when Ac asain introduced,

II, The questions: What do Ds and Ac represent? What mater
rol

commosed off iow do such

they come from? Are they
What can we find out about

a eLals are they
units arise in the nuclear cormlenent? Whe: e do
always tnere or are they so-e thin ng newly eva ted?
them that will help answer these questions?

wt

TIT, the above questions take us back to the very first discussion in this
series: the sudden appeerance of a great many newly arisen mutable renes in
the =rogeny derived from a set of ~lants, escn of weie> had undergone the
breakage-fusicn-bridge cycles A180, the differsnces in the mutable conditions
exhibited by two branches of the same “lant -- one giving a rusable, the other

not having tis rmtable,

“ome correlations between this en le and the

origin of the mutable loci suspected,

1. This history -- no previous investigations made on plants that had

undergone this chromoseme tr-e of preak rage-Pusion-bridve evcle,.

2. What is the particular stpihfigance about t-is evele that covld vroduce

these new mu_able loci?

mutable genes?

Why might it be res-onsible Sor initiating the
 

 

 

 
IV. Sxaminaticns mede of the enr-~osome constituticns in a nunmbor of the
plants that head undergone the chromosome tyme of b.f.b. evcle -~ between
250 and 300 dxamined.s Revealed a striking alteration of perticular

components of the chromosome com lement and this quite unexnecsed,

1. Alterati ns involved some kinds of changes in the heterocharcatic
elements of the chrerosome cormlement, tnvelving chromesctes other than those
of chromosome 9 as well as those in chrovrscme 9,

 

2. The regicns involved: The centromores, the knobs, the ends of
chromosernes, and the nucleolus organizer on chrozcsome 6,

is

3, The physical appearance of these covponents.

lh. The wosit’ ons they occupy in the resting nucleus, ‘ '
RAT mrp yepine ~ .

NEI

8 2s that occur between the kmobs and between the centronme es,

ements.

©
al, PeStine nuclei.

~

2: Th
in mn
V. The expected types of changes that should be produced by the chromosone
type of b.f.b. cycle: On board,

1. Diagrams on board,

2. If healing of breken ends occurs in the spororenous cells or in their
ancestor cells, the constitution of the chromosomes mav be examined in the
resulting microsporocrvies by analysis of pachytene stares, this could
show what is present in the chromosomes 9 that hed undergone tnis evcle,
Would expect duplications, deficiencies, reduplications, ete,

3. In a number of cases, the exvected txmes of alterations, as shown in
the diagrams, wore found,

h. In about lO or 50 cascs, other types of aberrations ot
chrexcscome con lement. “hese not cormon in plant that ha
fhis cycle.

os-pved within the
ve not unde pone

VI, The classes of abnormal trpes of chromosome alterations. Involve the
broken end or the knob at the broken end of short arm of enrososcme 9 with

other regions, or the centromeres with other wentromeres or knobs,
The types obse=veds: Classes,

1. Centromere to centronere aberrat’ ons:
q i +.

Long aun hy
'
Lo
'

2. Centromere to knob aberrations: O
, :

a). “ing chromosome 9 -- centromere to lmob

 

b). +nversion in chromosone 9: JRE
ce). Inversions in other chromosomes:
ge . _ ee
Chromesome 5 re Wr 7 *
—- oe
/ _
Chromcsome 7 oe 7 ~)
AN o,
Chro:osome 6 ewe tO -
t a
3« Knob to knob or broken end to knob exgitxm aberrations: -—~ .
~. bie
a). Ringe chromosome q. OO 7 $
. . a16 oz
b). Duplicetion: Or ee
. : os 4 V6 a
a). Translocation of end to short arm: ott ge

lh, Knob to knob end centrome:e to centromere: Cy
~ ty -

5. Knob or broken end of chr. 9 to knob on anothor ehre osom

@ Chromosomose 9 and 3, at kneb

f

|
te
a

B Chromosome 8 lone arm, and Eheo-osore 9

C) Chro-ioseme 6 at nucleolus orfanizers

 

vena Rp,
-l-

6. To end of short arm of chromosone & + many cases?

VIII, Conclusions: ng

1. Quite obvious that many other aberrations occurring as consecuence of
the b.f.b. cvcle than that wich covld be expected.

2. Ruite obvious that the majority of these unexpected aberrations
occur to particular elements in the chromosome cormlement -- centromores,
knobs, nucleolus organizer and the end of chrouosome 8 short arm.

3. Question: Is there any relationship between the occurrences of these
aberrations and the origin of the mutable genes? Can we test this?

lh. A single test made, which will be deseribed,

 

TL. Wotan a 0, ~ Dr The a, - Dt relationship anc the test for induction of Dt,

I. The aj, recessive, located in chrovoseme 33; used for many voars in maize
genetic studies,

2. this rececessive very stable. Reversions to A. in the usual senetic
stocks not seen; Attempts by Stadler to get revorsions by radiaticn not

»

O
successful alt»ough many thousands of cells irradiated,
3. the orisin of a mutable a, locus:

a). Randolph stocks: Black Nexiean sweet corn. Ay AL
_b). “ne plant -- on self-nollinated esr, kernels that were colorles
and those that were colorless with dots of color were serregating.

c). Rhoades took over the menotic analvsis,. Thorough analysis over a
period of a number of veers (1936-191 and lator),

(1) A new mutation to a, fwom A

(2) A dominant present, Dt for dotted, wich made thi 1
in pattern of dots of cclor in the kernel and fF treaks invtre plant, ~
“hese dots of color were dee: -- with the diffusion rims, previovsly described,
Very few early mutaticnss; very few mutations to the pale color,

S a, mutete to A

A be

(3) Seeastonal ant-er with mucant tissue, or sector of mutant tissue,
Pollinations from them produced the germinal muteticns for subseauent study.
These proved to have dominants that were not all exactly like the original --
all were hirher alleles of the Ay normal locus,

(1.) Tested Dt on the old kmown recessive, Cavsed it to mutate in the

very same manner as the one which occurred in the Black llecican Sweet Corn,
(5) The dosaze action of Dt: increased doses, increased fro-uenev of
mutation -- more dots, reometire in some cases,
(6) Obtained sone ay recessives through tis process of being with Dt

that no longer mutatédnin the presence of Dt,
(7) Located tis dominant, Dt, adjacent to or in the lnob te minating
the ssort arm of chre-osceme 9,
II, Tho reasoning that lead to experiment to produce Dt by the b.f.b. cycle.
1. ay does not mutate in the absence of Dt. It is very steble,

2, If the b.f.b. cycle makes evident the controlling

 

factors, such as Ac or
Dt, and does so because it dispubts the heterochrometin or its balance in sone
manner, then we should be acle to get evidence of the origin of such a Dt
factor if a; /a, plants have chrevos mes undergoing the b.f.b. cvcle,

3. This can be done readily, as will be shown,

h, Would expect to find mutations to color -- but in sectors and showing
dots of A, in these scctors
This reasoning is based on our knox fledge of that state of the normal
&@, locus:

this state gives dots with Dt. Uther changes probably occur -- and
do occur since stable a, in presence of Dt obtained -- and these wecogsnized
by the pattern of dots in the kernels navine Dt,

Also, we know have other states of a, -- found by Nuffer to have
arisen in the Dt stocks These give trmes of mutetions Like t ose shown
early -- e-rly sectorials for both full Ay and for pales, and various ccanges
in state arise frequently from them,

TIT, The test procedure:
1. the cross:

Female Male

@, fa, Vowel &qwplereet® Ja, C
try.3 Yount Olb, 2. a po ee

2. the gametes produced by the male?
(1) Cowpea Dep, wo (nkioy cea
(2) Raf, Wry. : won ferret cued potlow.

(3) plowreres ward wi hohioes cess

 

as

 
c.

4. The chromcsome constitutions r sulting from broaks (1), (2), (3).

5. The functicnal pollen grains: 4 vy have a newly broken end,
my . 44 , : 4
those grains with nesr normal constitu yak short

 

duplicat?ons function more efficiently wius the

full duplication of the short arm,

fe

6. The control test of this functionine:

Fenale Male Ddtee - ala,

PAR, ele ce

the results: See enre be p.
IV. The results of this test:
315 ears obtained: contained a total of 93078 kernels,
3

117 kernels with spots of color <= the Ay type wit» diffusion rims,
All were dots, No pales, no large A, colored areas.

these vresent on 86 different ears,
The number of dots per kernel?
93 -- 1 A, dot only
9 -- 2A. Gots
1
~- 3 Ay aots

i

?

-- A, dots 5 p ration , Dota

we 5 A, dots 5

7 A dots
1
—— 17 AL dots

MF Mm FP oO
1
!

-~ 8) A, dots distributed over the whole aleurcne aveag

The apnesrance of the dots, wnen more than one opessnt, in sectors,
'T yoo ~
the resemblance to the dots produced DY Dte

mM - 4 ‘ a h - en a
V. the reason for so few cases being found: The Dt factor must be vroduced
carly enough in the develonment of the kernel to have an effect on the cells
late in development,

mp 5 2 : + 4A A ~
Ll. the time when these chanres covld occur: ror Anaphase II to excrly
endygsperm divisic

&
ns in order to produce decided sectors:
in divs

oO eet . . . ‘ ‘ ‘ ~
WB Division in pollen frain? \ '
vie ae ; ; . t ul
\ iirst division in emfogperm: la a he
, co = 2 s * e ia ‘
‘ Second division in endosperm: ty.
Th tand Atere4 . ’ IZ
+hird divsion in endosnerm*
“ourth division in endosperm’ lig
VI, Experiment positive, Shows that Dtelike effect can esnncar in tissues
that are undergoing the b.f.b. cycle.
VIT, The presence of Dt factors in strains of maize: Tose from S.B.

examined:

One strain from Peru and one froyx Brazil found to have Dt,

in both cases, the Dt not distinguishable from that found by Rhoades,

Mn one case, the only one whose test “as been recortec, the Dt
factor is not in chromesome 9, It anooars to be in chrovoccne 6,

These differences in positions -- corresponds to that of Ae,

VIII, The indicattons so far, suggest that these controlling fact

: eo
ar, t ling facto:
present or can de nade evident in nuclei, “heir possible significanc
be discussed Latere

Vha Cane 4) «ver P - ke
the re 4 Pelrson