, Lecture 3. January lt~, 1951!. 1x\s. p :d t . c.i ,v7 The`locationhjand cytological behavior of Us.+ d %n,IS A :s I, Review of >-?revious discussion 1. Began discussion of variegation Droduced by loss of segment of chr. $! 2, The pattern of loss during development of tissue followed that shown by mutable genes -- those whem mutation occurs from recessive to dominx&, a). Iq mutable gene, mutation from system. recessive to dominant controlled by b). lime and cell i--b which mut.ation will occur is due to tiis s;,xtf>rn. 4. "omatic segregations of factors controlling system Alters time and frequent:,? of mutstion~in descendent cells. 3. The loss phenomenon -- follows this same ::attern but inste,:d of mutatio the-e is loss of a segment of chro:3.0 so-e 9 she x't x3-n. 4. TWO appa;-ently differ,:nt variegation phenomenon have something ve-(y much in common. f .* Both seem to be governed by something ozcurring at a locus in a chro,.losom?e during the mitotic cycle, effect obviously on chromosome, The chromoso.-le loss phenomenon -- II, Need to determine nature of the event involvin,~ c):roi:oso.-e loss as it could t'?rou,gh light on t3e nature of the mut:qtion Process occurriy?g with. mutable loci. 1, First question -- Is all of the c&:nosor";e lost? in chrom some i:-,volved as w?th mutnble loci? Is one position Is it specific3 III. 'I'he initial test to answer these questions 1. Test started last period: Female parent lie C wx / Re C wx i'iale z3aren-t I Wx / G wx from vxriegated kernel. 2, The ear -- I Wx, var. for C wx kernels selected. Zlants grownfrom them. Their constitutions: 30 Normal chromosome 9 I wx %xverziion " If For no crossing over in c wx short arm of chr. 9. i-fp 1. 1 i's~?:)bI~`.(. .,.id . 4, This.plnnt, as 7nle, crossed to plant with C wx:; &emels on-ears (11) pernels on resulting ear 1 co&orless Wjj I" i 1 with wx areas 2 Colored wx, non-variegated, -2- (1) 6, Conclasions:4Something carried by the I l!x c:-iro~:loso:ae respnnsible for losses. (2). Somet: ,ling else necessary for losses to occur. Only +.of the gametes with I Wx produce kernels that show variegation. , Xijl" t,;,. A!` I_ ., I I, g;;,,, ' . "I! (3) Ratio suggests that ssp arate Z?actor present in male parent: ' Only half of gametes get this factor: Gametes /, ,-R:a i b Iii.. I Wx with. factor y& 'Q :;; -y. ,,;A . 1'1 ~1 ,* .i-ir, 0 ( (4). 1 Wx, no factor. This proved to be true. activator. It activates the breakage Factor given the symbol AL, for events in the I Wx cZ?.ro,?osome. ??? o 'his plant: (AC ac) in cross to Cwx I I Wx/Cwx 1Ac ILernels on ear Its gametes: I i?x No AC I wx I Wx, non-var AC present I Wx; C wx areas Cwx AC Colored C wx, no AC lf Will consider AC next period, III. The tests for the location of factor in I Wx chromosome responsible3 for loss. '> ` x 1, Above plant: Normal chro1r.o. 9 I Sh Bz Wx/ Re C Sh Bz wx 1 AC < 3 2. Crossed to female homoz;-gous for normal chr, 9 with C sh bz wx. $ $5 -2. 3. Gametes hacrying I Mh Bz Wx and AC produce kernels that are variegated: Sectors present that are C sh bz wx, This due to somatic losses of I Sh Bz Wx during development of kernel. \ Appearance of kernels. 0 Photographs of kernels. The Bz rims. _ "1 gp4 M-Y- .WIC,UII..," .,--r q-2. m- ^I-_ *___ .--, ___1/ '5 ') 1'; '_II . 4. Th,ese variegated kernels selected from ear. 'heir constitutions' Plants grown from them I Sh Bz Wx / C ah bz wx, AC 5. These plants crossed to plants that wer;e C sh bz wx, no AC, 6. The gametes carrying the I part of chro-loscme: 14Sh2Bz ?I, I c&g v n Cahhzw wx Genot::Te of Ehenotype of k-rnel Non-var. male gamete Non crossovers: I ShBzWx I Sh Wx Region 1 1 sh bz wx I sh wx II 2and 3 I Sh bz wx and I Sh wx I Sh Bz wx Result: Only chromosome with Wx shows breaks. The C class of kernels on the ear: Non-crossover C sh bz wx C sh bz wx ---u----w 128 Region 1 C Sh Bz Wx C Sh Bz Wx 2 tt 2 C sh Bz I?x C sh Bz Wx 0 2. 3 C sh bz Wx C sh bz Wx 31 59 5 52 Var. 57 0 0 a----- 5 1 22 later. Total, Plus: 2 odd kernels in I class -- to be discussed General appearance of the ears showing such ratios: 7. Conclusion: the loss phenomenon, Some factor, located to right of Wx, responsible for -- .. -- .-__ present. -. O.&e&&e, These will occur, howevJ:r, only when AC also no losses occur. AC will not induce loss in chro:::osome without the loss factor being present. 0. The second test cross for location of factor: Same male @rent to female parent homozygous for G sh Bz wx, no AG: the kernels that are colored. We will follow only pi&-`; Gametes a). The non-crossovers: -"ernels Non-var. Var f?j + . C sh wx 99% l$ .Jtzsz=k RegTon 1 Region 2 C Sh Wx C sh Wx b). Again, factor in I Wx chromosome -- to right of..Wx. __- _--- ..- Tine few C to c var. kernels in C sh wx class indicate factor is very close to Wx. .d.. d. When this factor present, to produce the variegation, loss of all markers to left of it occurs _ -:$I& G t &g? b%-. 1% d), Question: Does a brea~~~.~~~.~~-~~~~o:.~o~o~~~~ because of this f.Lctor that pro,duces .loss,es.? --,. . ~ . '+/h-at, happens __.--__-.-------.-.I_ ___-._" .- .-_,..__ _---. 1 . . . .". .- -.--- IV. Cytological exa&nation of the breakage mechanismc 1. Piece lo$st is large -- could easily be seen in cells. 2. Losses occur in sporogenous tissues -- be examined for tcese losses. therefore sporoG;+es Gould 3. "he reason it wa s known that losses occurring in so171e sporogenous cells. Pollen examinations of plants carrying I Vx and factor % C wx no break factor. Normal pollen from I Wx / C wx, no break factor. 1 wx : 1 wx Pollen from above plants. (t&th DS and AG) Not 1 : 1. wx . Nore wx grains than A number of nearly empZy grai.:ls, Di?ference between 1 : 1 due to losses of I Mx part of chrc 4. The appearance of the mnize cbro~osp:~es at pro-ihase Of meiosis: a. The premeiotic growth of chro;-osomes. b, The meiotic prophase chromosomes -- long rods. "ynapsis. e, f. Q. 5. c. 'he met'-od of collecting sporoc:tes and making examinations, Tassel s,am;>les; anthers selected; sporoc::tes squeezed out on slide in drop of stain; exa:>ined microsco:?ict!lly, d. The 10 blvalents at pachytene Rhoades, figure 3 .`\ 6 \ :' Note. 10 rod bivalents - w size differences The centromeres - The 5, 4 78 9, 10, 2 mobs, 7, The nucleolus, nucleolus chr. n, or. The contraction period. Rhoades fig. 3 Diplotene .,.,,, ( LG. Diakinesis - Zhoades figure 3; "etaphase I. %oades, fig. 3 (.I AI to A II - *&hoades, f-igures 4 and 5. cil qglc c (`j" 3 ', The constitution of the plants first examined: Prom cross of Female Male yg C wx ds no AC Yg I Nx Ds, AC. Selection of the variegated kernels I Xx with C XX areas Plants grown from them. Sporocytes examined, Their constitution; appearances Sporoc~d~c:s collected from tassel. &x,unined. ';'howed: 1. IGzny cells with no,rmal bivalent chro.4losome 9: t F 2. Some individual cells showed break.'*" .~ v ' V Position fits genetic evi>ence of locus of factor. j. Some sister cells showed: 4. Cluster of 4 cells in anther: 5. Conclusfon: Breaks are occurring at position in chro~o~~e where genetic evidence had located the ghenomenon, res;:.onsible factor for vaAegation 4. The question: In cells examined, carries the factor. could not tell w:-lich of two chroLmcsomes Do breaks always occur in the Ds carr:-ina chr? Do they also someti+:les occur at same positTon in the homologue? a). This tested in following way: The two members of the bivalent chromosome 9 must be distinguishable from one another in ti?e sl:ort arm, In this way, it can be proved whether that chro?losome 9 carrying the factor. or not the breaks occur only in b). How individuals I heteromorphic for si?ort arm of chro;?oscme 9 obtained, Plan% with i:;:3 Plant 14th c- -c&d v-. - c ;L- I, '$ Q. \a + c c -... . .--- ./, n t -. -i ..-. ._ in*c\ks b ne " kc. AA,? fh On ear, I knrnels with C are6s present. plants grown from them. These selected examined. 7-i?& / \q&&&&-q me s?orocytes collected and chrc -:osomes in'them ,--.,.~~~-t)--- - e-- -. \9 * 4. The observations: I' + --c- Dr 1. xany cells >zith bivalent: - .a b--- b c Y 2. jome cells, scattered her>e and tzlere in ant?..- with: -----3 I e--- ---- . ?' 3. The lack of synansis of part in the acentric fragment r-rith homologuols chro~-~csome, I-&$?- ,y 4. The vremeiotic breaks: -w I , +vL jj.&, * a): Y-, .--- y--