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_ Leeture 3, January 1h, 195L.
ger” oe Q -
The “location ;and cytological behavior of Ds.< yom fe

—

A
I, Review of nrevious discussion
1. Began discussion of variegation produced by loss of segment of chr, 9

2. The pattern of loss during development of tissue followed that
shown by mutable genes «= those where mutation occurs from recessive to
dominant.

a). In mutable gene, mutation from recessive to dominant controlled by
system, “ime and cell in which mutation will occur is due to tris system,

b). Yomatic segregations of factors controlling systcm

ce). Alters time and frequency of mutation-in descendent cells,

3. The loss phenomenon -- follows this same sattern but inste:d of mutatio
the-e Is loss of a segment of chromosome 9 short arMe

lL, Two apparently differsnt variegation phenomenon heave something ve(y
much in common,

5. Both seem to be governed by something occurring at a locus in a
chrouxosome during the mitotic cycle, The chromosome loss phenomenon --

effect obviously on chromosome,
II, Need to determine nature of the event involving chrovosose loss as it

could through light on tne nature of the mutstion process occurring with
mutable loci,

1, #irst question -= Is all of the chrnosome lost? Ts one position
in chrom some irvolved as with mutsble loci? Is it specif
III, “he initial test to answer these questions

1. Test started last period:

Female parent tate narent

Re C wx / Re C wx IwWx /C wx from
variegated kernel,

saan

2. The ear == I Wx, var. for C wx kernels selected. Plants grown P rom
them. Their constitutions:

 

Normal chromosome 9 I Wx . .
36 For no crossing over in
“nvergion " " C wx short arm of chr, 9,
AK ea ari route. chon
OW : PT aU
v kh, This plant, as mle, crossed to plant with C wx: Kernels on-ears (11)
- ‘\ 600 I Wx, non varierated 1 .
Re ’ RR 0 = of I} ore] 2 5
yo 588 I Wx, areas of 6 wx nly g of I Wx kernels ave var,
ae OP 1550 C wx. hy
Oye . _ wy ft Te : volar f
‘ eR b\ the of Spal we MUR CE ead | .
. . . eo foe
a 5. Same male varcnt as « crossed to plant homo.vgous for c wx: a
; Pp Eg —.
. ES.
ermels on resulting ear 1 colorless Wx an
Yuba o if .
: 1 with wk areas

(D 2 Colored Wx, non-varierated,
(1)
6. Conclusions: Something carried by the I Wx chronosome responsible for
losses,

(2). Something else necessary for losses to occur, Only #4.of the
gametes with I Wx produce kernels that show variegation,

pl oaeer a cok ny * . “h
(3) Ratio suggests that separate Factor present in male parent:
Only half of gametes get this factor? Gametes —
i Pr aS
I Wx with factor Aye Hoo ~ a ty
eo é ;
WAR wil. t 5
. . = Wx, no factor,
(4). +his proved to be true. Factor given the symbol Ac, for
activator, It activates the breakage events in the I Wx chromosome,
(5). “his plant: I Wx / C we 1 Ac (Ac ac) _ din cross to Cwx
7 Kernels on ear
Its gametes: I Wx Wo Ac I Wx, non-var
I Wx Ac present I Wx; ¢ wx areas
C wx Ac Colored
C wx, no Ac 7
Will consider Ac next period, Y
oS
III, The tests for the location of factor in I Wx chromosome responsible ‘WN

LP
ad

for loss.
1. Above plant: Normal chromo. 9 I Sh Bz Wx/ Re CG Sh Bz wx 1 Ac

2e Crossed to female homozygous for normal chr. 9 with C sh bz WX. %&

freteetans

3e Gametes harrying I Bh Bz Wx and Ac produce kernels that are
variegated: Sectors present that are C sh bz wx, This
due to somatic losses of I Sh Bz Wx during development of
kernel,

 

 

Appearance of kernels, Photographs of kernels, the Bz rimS.
> Agl. “ Mm Att, or a7

fis ta
om

 

lh. These variegated kerngls selected from ear, Plants grown from them
“heir constitutions’
I Sh Bz Wx / C sh bz wx, Ac
5. These plants crossed to plants that were C sh bz wx, no Ac,
6. The gametes carrying the I part of chromoscme:

2
I Sh Bz Wx nabs

Oc

C sh bz w Wx
-3-

 

 

 

Genotyve of Phenotype of kornel Non-var, Var,
male gamete
Non crossovers: I Sh Bz Wx I Sh Wx 59 57
Region 1 I sh bz wx I sh wx 5 0
" Zand 3 I Sh bz wx and I Sh wx 52 0
I Sh Bz wx
ne, Result: Only chromosome with Wx shows breaks,
wn
The C class of kernels on the ear:
Non=crossover C sh bz wx GC sh BZ WK wmeeee ene 128) ween
Region 1 C Sh Bz Wx C Sh Bz Wx 2
" 2 C sh Bz Wx C sh Bz Wx 0 1
8. 3 C sh bz Wx G sh bz Wx 31 22
Plus: 2 odd kernels in I class ~~ to be discussed later, Total, 36
@) plea.

General appearance of the ears showing such ratios: Illustration Bare

7. Conclusion: Some factor, located to right of Wx, responsible for
the loss phenomenon, These will occur, however, only when Ac also
present, Otherwise, no losses occur, Ac will not induce loss in
chromosome without the loss factor being present,

8. The second test cross for location of factor: Same male tmrent to
female parent homozygous for c sh Bz wx, no Ac: We will follow only Phd,
the kernels that are colored, - an =

Gametes *ernels (2) ver
a), The non-crossovers: Non-var. Var.
C sh wx 99% 1%
. i Region 1 C Sh Wx 50% 50%
CM ees
Region 2 CG sh Wx 50% 50%
b). Again, factor in I Wx chromosome -- to right of Wx, The few
C to c var. kernels in C sh wx class indicate factor is very close to Wx,
ce). When this factor present, loss of all markers to left of it occurs
c to produce the variegation,
er , mare in at a
on. 1% da). Question: Does a break gccur bere in chrouosore? whet happens

because of this foctor that produces losses?

cease ent teat Ok Ht easing acme we ater wns

|
IV. Cytological examination of the breakage mechanism.
1. Piece lodst is large -- could easily be seen in cells,

2. Losses occur in sporogenous tissues -- therefore sporocytes could
be examined for these losses,
3. the reason it was kmown that losses occurring in some sporogenous
cells, Pollen examinaticns of plants carrying I Wx and fector YX C wx no
break factor,

Normal pollen Pollen from above plants,
from I Wx / C wx, no break (with Ds and Ac)
factor, Not 1: 1. More wx grains than
Wx. A number of nearly empty
af 1 Wx: 1 wx graics.  Dirference between 1: 1
qe due to losses of I Wx part of chr,

l.. The appearance of the meize chromosomes at provhase of meiosis:
a. The premeiotic growth of chrovosomes,

b. The meiotic prophase chromosomes -- long rods, ~ynapsis.

c. the metrod of collecting sporocytes and making examinations,
Tassel sarmless; anthers selected; sporocrtes squeezed out
on slide in drop of stain; examined microscopically,

d. The 10 bivalents at pachytene Rhoades, figure 3 G) @

Note. 10 rod bivalents - size differences
The centromeres - 79 9, 10, 2
The knobs, 7, 5,
The nucleolus, nucleolus chr. n, or,

e. The contraction period, Rhoades fig. 3  Diplotene Cu

Bw

f, Diakinesis - Rhoades figure 3; “etaphase I, Rhoades, fig. 3 (wv

g. AI to A II - “hoades, figures }} anda 5, (5) +(6) .
a Ve

B. The constitution of the plants first examined: From cross of
Female Male
ye C wx ds no Ac Yg I Wx Ds, Ac.
Selection of the variegated kernels I Wx with ¢ wx areas

Plants grown from them, Their constitution; appearances
Sporocytes examined,

Phent tortih\ lie ‘4 LT . yo ” - a

5 b } Y - . i
‘Te ay “AD DAL Ye.

Mt
a4

LL LAL.

Meo Loe Po Be, 0 ai
we OE ‘ ac Me
ta a tee 1 ~

g .
Meo Poe Mae ‘
~5.

Sporocytcs collected from tassel, Examined, Yhowed:

e
ot

1. Many cells with normal bivalent chromosome 9:
Bane e

. Ss dividual cells showed break:
e ome individual ceits . genetic evidence of locus of factor.

3. Some sister cells showed: et

So~ X i : Bo. ep, 7

\ . Abe
ai \ : (ers Qf
fe \ . os ~~ ei

LN ae }> j

4. Cluster of lh. cells in anther:

6.

5. Conclusion: Breaks are occurring at position in chronom me

where genetic evidence had located the resvonsible factor for variegation
ovhenomenon.

hh. The question: In cells examined, could not tell which of two chromesémes
carries the factor. Do breaks always occur in the Ds carrving chr?
Do they also sometimes occur at same position in the homologue?

a). This tested in following way: The two members of the bivalent
chromosome 9 must be distinguishable from one another in the short arm,
In this way, it can be proved whether or not the breaks occur only in
that chromosome 9 carrying the factor,

b). How individuals heteromorphic for short arm of chromosome 9 obtained,

PF
' ted

+_
Plant with Plant wi th
J weds ry
- Chan Yo He * Aas Coe .
On ear, I kernels with © areas present. These selected,
plants grown from them, The sporocytes collected and chrc“osomes in’ them
examined, a: AY Coho LOM -—~---- oo a ie his
Oo pee :
¢). The observations: De
1. Hany cells with bivalent: an a: . (a

Pe ©

2. “ome cells, scattered heve and there in anthor with:
Sooo | f

Orne oe es

a we
.

3e The lack of synavsis of the acentric fragment with homologuovs
part in chromosome. .
Dhle-.9
lh. Lhe premeiotic breaks:

» Ss ii .
het, Roa. [dp
4 s a pe wre
A) tag = -- pv 2 ~e +
ye TT -
\
¥ Ww

oa
dH topic S Apna wo ws fowls clade ell

VD CD fy”

ce). the observations, Phd

OT Saal, A iv, , eeeeet [au fo
a he ode MOU & Yur xo D, é i 7 t | he , , Meal - ‘ @

eo
6. What takes place at locus of Ds to produce the disscc&ation?

a). Normal chromosome reduplication gives prophase: *

b). “hen Ds present, and a dissociation event occurs, it results
°
in: go pe
wun X. on

c). “his suggested initially by presence of bridges in the
' second meiotic mitosis:

Usual anpesrance:

Some cells :

 

d). Wow these latter produced:

FE

wet e j . f a H ,
AYE) Hi ec to
yy F
i
- Gor ee ve * Po
° “ .
t——> CB. :
Ve the additional types of chrososome altsrations produced by Ds.
hey are a small fraction of the total, Most events at Ds
mproduce the above type of altcoration,.

1. The translocations: One breakt at Ds in chromosome 9 short arm?
“ound in few related cells in an anther,

 

is
2. Inversions: . foo
u. ee ve ti
a ‘ £ is een :
© o meen 7 e ae Oe
r 4 * a
A
e
3e Duplicationss: Oo
Cth beceeany
e-
o
lh. Deficiencies: 6o- zr
° mT
5. Ring chrom s omes 9 L. ‘

6. Few with more comlex rearrangements involving short arm of cir. 9,

VI, Emphasize: No bre-ks of any sort occur at Ds unless Ac is also present.
Ac not in chhw-osome 9, Shown by earlier ratios,
Ds is completely stable without Ac -- generation aft r gener,
VII, Ac should not be considered. Where is Ac ? How does it act?

1, Review: In above described crosses, half of gametes carrving
Ds chromosome have Ac and other half, no Ac,

Suggests Ac carried by separate chroucs -e

7 Segreratod
at meiosis indevendently of Ds chromosome,