2nd lecture, Jammy 11, 1954 The discovary of Ds. Its behavior and its relation to mutable loci. I. Review.of previous talk: 1. Sudden appearance of a large nun&r of newly arisen mutable genes -- expressing variegation-- in progeny derived from self-pollinatfons. 2, The origin in plants that had undergone the chromosome type of breakage-fusion-bridge cycle in e-?rly development. Healed broken ends of chro-?osome 9 in recovered branch. 3. The various t2pcs of plant dnaractitrs showing variegation. Various types mentIoned af'fect;ng chloro-hyll eqression. other characters, More types later affectin 4. About 40 different origins of mutability recognized in early experiment 5. The features shown by the seedling exhibiting variegation: ?? o Background - altered phenotgr-e, b). On background, streaks of normal phenotype c). The normal streaks present in a decided pattern. Reflect: (1) Time of change to normal during develorjment of tissue -- determines the size of the streak (2) The number of streaks: reflects frequency of occurrence of changes to normal phenotype durring development, . (3) l&e relative distrw of streaks: reflect the distribution among a growing tissue in w!7ich changes occur in specific cells, (4): The dj.fferent t$Tes of patterns: The Seedlings: Many later occurring changes Few late occurring **any early '. 1~ '. ., c+hnnges. Changes . Leaf' [ i \ '_ '; a mosaic of many i' \ * patterns. ; 4 I\, I i I \ d). Within a tingle progeny, one ty:je of pattern usually predominant. 6. The changes in the pattern of mutations occurring dur-i.ng development. ?? o Sectors fomned: I), Lncreased number of streaks 2). Decreased number of streaks 3). MO streaks 4) . Large mutant sector b). 'he twin-sectors: One sector co ,posed of two parts: *ypes: I.{. Eaormal phenotJ?e: altered phenotype - no streaks c II 11 I? If . : - aincrease or decrease in number of streaks. 3). No streaks : increased or dec?%eased frequency of streaks. 4). i ncreased frequency of streaks: decreased frequenc:,T of streaks. 4. . Each component of twin derived cell as iectors arose from s?ngle consequence of a mitotid.~ which produced two sister cells. 7. Inter-oretation of the nature of the change that,occurred to give rZse to n* -Ye or twin sectors: ---.-----j_-.-.-..I-x.~-._____, ,_-__." ___ _ ". ._..... ,. ___ ___x ._ _.. __ ._ 4. Particular i,attorn in seedling leaf reflects a controlled t;Te of expression ofQtime tJhen mutatl.ons will occur, will. occur& \a&$;\ _ &A+4 L* &,I' I 6:: 'ha4 an+ the ce:-ls in which the:, b). The factors respomihle for this control may be Utcred as a consequence of a mitotic event. 4. hollowing altereatlon, there ~3.11 be a different pattern of mutation in the descendent cells from that present before the change occurred, d). The twin sectors suggest that cantr.ollinff factors segre,ga-t,e. at-a mitosis: one cell receives so=?et'ling that the sis%er"%?$j~~"~'*fost. a). 'he mutant - altered pattern twin sectors: Suggest that the Dutation itself~conse~ence of a mitotic event alterin~.so~nzctillng, --* ------.-----.__y.~l-"l Lo -_-II .I_- .,.. . . . . . .-._ . ..- _ . 8, The major questions and propositions: 1. What factor or factors al-8 responsdble for ~?rodt:cS.ng a articular pattern of mutations during development? i.e., (1) the tIxe during the develo-;-,ment of a tissue r-ihen mutatZons will occur, tissue in ti2ich t,is will occurs i.e., (2) The cells of the the frequency and distribution of c changes that will occur in particular cells duA.ng develo;Gment, 2. How does the factor, or do the factors segregate in certain cells as the ccnse;:;.uence of a r.1itotj.c event? 3. 1s the T-)rocess of mutation associ-.ted wit?! t'ne saze type of event? 4, What conp! nent of the nitotic process is involved? a). 1s it a segregation of c:Ftoi3lasmi.c coE?onents? s it related to the chrmosozes? To changes at SJ- ecific loci? it related to tine nrocess of chromosome reduplicrtlon? -3- II, The peri.od of decision and t c early investi,~aticns. 1, Original ~rupose, to analgse t'ne gexic components within the s?ort arm of chro*xosome 9. 2, Tie presentation of a wholly unexpected phenomenon - the variegations, 3. Gradual conviction, following growing of thev ariegnted plants -- that the phenomenon involved in the eqression of val5egaLlon was far more in-iortxnt than that of t'ne original purposes, stated above. I!.. How could this phenomenon be investigated? 8). At i'irst, did not I~rnow, b). As first step, c&cided to-,&&w t.e.~.J~&er$,tance behavior of a number of $&le~~l.ee.d.. cas;;s; and the inher ante aspects of the pattern controlling systems. Ihis in order to get facts with PJ 1.ch to think. 5. l'iirst year and a half -- Results confirmed earlier obs=rvati:.ns, Showed that the al te~."~~.~~~.~~~.~~~.s.e .ci~hnges. at the 10x1~3 of. a particular fw-*: ",,-..-.A.>,." *,-- __ .-__ -., a mu-able gene The change resulted in mutation from recessive to dominant, (F~~~.cNC~. The control of the mutation process not well distinguished in ezrlg studies but suspected a similar type of change as that :-:roducizg mutation, ation 3g3te.m. that ,altored the ch~~,~.::iosome ~e~y=&~t-y-2%.~y*y~ -mp.p ^-"-.. -.. m. de 6T- -8-e B y.gt-f on : 1. %W A part of short arm of &ri-:.osome 9 elim,?insted in certain cells durFng the development of a tissue, 2. The pattern of such losses in the various tissues simul:!ted the patt::rns nroduced by th.e mutable genes, &ere mutation from recessive to dotinant occurs. Loss;': .& 'I 8.1: Hutations %I / , ?,'. 1)1!L ! ,,'"1. -. ,,#`, 9' : i , ,\ ' i I `?, &y/,(//J i i':: .'S "' y-' t'. ;, \ . ",Ai' !I g 1 i, I? '\ ! j -,?,f *\I:tlJ ?- y&b j . `I / :] i ; ; i )'I I' 1 I i 3. The ch=anges in patterns of loss, as seen in'sectors, slnflal- to the changes in mutation time and frequency noted wrth mutable loci: r. -~ ,,+A , : x :. n, . .`_, \ "<,> `?! 1. c -4-m 1, First seen in soze kernels der3.ve.d from self-pollination of one plant th,at had undergone chr, mosome tpe of b.f.b. cycle In early development 2. 'his plant -- carried two chro ::oso?es 9 t*3th newly healed broken ends. 3. The genetic factors carried by each chromosome: 4. The know them W, I, W C Sh Bz wx -o- .a....*. factors carried in the short arm of chroxosome 9 -- necessary to to continue study: w; I's, yg. -- At end of short arm. c, c . Sh, sh Bz, bz wx. wx (a) Crossing over between markers (b) ?hysical yosit5.m in chrlomosoxe s ILLUSTPATICNS ol's-, c = 5. The pattern of variegation exhibited on some kernels of x&F-pollinated ear: Z V, The structure of the maize kernel and its development. 1, Nust understand this for any discussion of maize genztics or cyto- genetics. Xi11 be given diagramatically for those ~CO are not familiar with the moqhology and develonment of kerne3;, 2. The morphology of the ma&e kornel: (ILLUSTXTICNS 5:- %t kernels), View from C33s-s section -- longitudin al. -.- --. \ 3. The origin of the endosperm 'and embryo 3.n the kernel, a). "he ovule on ear, before fertilizaticn: Ovule Hegaspo~oc;~te f I: Meiotic mitoses Megaspore b). The development of the embryosac: y pqyq /wq&`;\i,i 1.) A'---. 4. The development of the male gametes: a). yhe young tassel, inside of leaves: telescpoed effect, b). Composed of' flowens along branches of tassel. d. s;cch flower has three ant&i-s d) . Inside anthers at micrcs;3orocytes. young stage are enlarging cells - the e), 'i?ne meiotic mitoses and development of microspores: - 6.. 5. '43.e process of fertilizktion: Pollination; pollen tube; break into embryo sac The nucle:.r fus?ons. The embryo and endosperm develop. VI. Return to case of chro:..:osone loss var~at-~_~ln. ---.-.e--.-e.w.a"e..m~..",~ _). ". L .yy. _ The partlcnlar kc:nels 1. Assume f'em&le cwx/cwx x male I I%x 2, Loss of I and Wx during development: ArBtas of color in aleurone, Unde:.lying areas, exactly corresponding, wx, .* IL' t 3. Cross section of kernel: il: l'.\ " 7' ' I ' , I * ' ', ,' . \ ,\ i 1 / ) 4. 2%: a). Exceedingly uniform in some kernels with regard to E$ ze and distribution of recessive spots, b). Not like pattern produced by other known mechanisms that r.au3.t in losses of chrmo soze s : 'he breakage-fusion-bridge c:;cles Ring chromosoc:e be&:vior, 4. Conclusion: A previously undiscov::red mec?wnism at work he:-e that produces the losses of I and I?x simultaneously, L 5. PJants gzi.am fm P mm--*- I____ ._I--. &ed-,kernels. %.-x.,~~~,zGz7z-~~/`.. -,;-` Showed: a). White streaks on normal green background: A ' / vl,q"ow c-34 ,' b). k+j&~ ".L+." ,--.<7 -p ed ' 9 e2rlier or nfa%~F"?9r3ing OF fesses. incr a-ed ox* decraasod f:>.-iBr:uenc:: of d. The twin-sectors: No losses -- hcreased or decreased f'req. of loss Altered pattern of losses in ez.ch sector: uften fncreased in one and decreased in other. 6, CmN%sion: The mechanism resoonsible for 1-s of @XQJ,QQ.SO~ -_.-.------ -----._--- _I* must be basicalllu similar or the samas that ~rocI.~cin~~.~~~g~~e~~e .m~&atko~ns. .-.-_ "-~------y. . . ..-. _ n -.-- _ .e- L 1_------- ..* * _., .r _. I I .~-~ Jk .*..,::... a). xhe f'los s 11 corresponded to the gene mutation, recessive to dominant. b), ?he system controlling the time of loss; and the cells in w2?ick it will occur is the same t:-pe as that controlling when gene mutations will occur in the c&es of the mutable genes, cl. Somatic segregatlnns, occurring at a mitosis, of the factors associated with the controlling system occur during develo:-.ment and this results in altering the time and frequency of losses in descendent cell?, d). Some reciprocal relationship exists in the two sister cells resultEng from this particular type of mitosis -- as if one cell gained soxethlng that the othr:r cell lost. in cox12arison with system present in the mother cell. 7. The summary: corn, risons between chr. loss and mutbble loci: a). ?&table 10~9: Mutation from recessive to dominant; Not chrcJY!osone loss. System present controlling when these mutations will occur. Controlling s stem altered as consequence of a mitotic event. ResultSng two cells di.L'I'erc from mot!leu- cell. b). The chromosome loss phenomenon' Very same kind of mec:.,::nism involved. Change occurs resulting in chrfimoan~~e loss &y-stern controlling when this will occur 'h&s system altered as conseouence of mitotic ' Resulting cells differ fro& mother ce3.l with event, regard to this, 4. Sometl:?ng happens to chrczosome to result in loss. v-hat is it? ?? o *he 10s~ mst b~.~~8~._-tt;g.~~~cc.lvide.~q nearly all of s';2ort arm of chromosome 9 as i @en. ,in 3% .w&.~.~: -__-.- .,..... "-"I ..% .n ._,, Lpsses of' W, I and E. e), `I'hcref'orr, t :3 im ~~~A3.~is-~.Jacfi.-tr;! m&~rossopic e2;mxi~~ati.m. (1) Should be able to find evidence of t-is loss; (2)Thi.s has been accomplished, and will be described in detail +;ortly, '- \&I `l$ ebz Fiearranged chro.;osome 9 Almost eliminated crossing over in short arm of c?lrom. 9. L b). Selected I Wx kernels wit3 Cux areas - the variegated kernels! & "2 --- --...,,.. _._i .-_. I._~_".,__., . . . -._,, ., _ _ fi 4. Plants groom ?rom them: constitutions: c e--+----- -- _ ___ ------ II' d). &hese plants L crossed to (1) female plants carrying C (2) female plants carry c e), The @yes of kernels and fre-uency of cross (1): type on resulting eal;s6` Table 12 a (page 16) in AC account, 11 .ears gave 6~ corn--:letely colorlesi : f33 colorless~wit3. spots of C : 1550 colored (C). Impostant: O-e-half of the I carrying chrc..-.osomeswere ---____1 I_ "___.. -.___,_. ._. '-SW .._-'-"-I.___._.-._-____- "" ._-._.. . "~^ . . ".X2"..` f). yypes of kernels on ear resulting from cross (2): to c With very few exceptions, ratio of 1 - colorless (I) : 1 colored. No regular tyjae of C to c variegation, f). Conclusions: , (2). Qnlp half ofthek,mels receivinxthe chroxosome 9 from the original vzriegated plant show:d these 10s~~~. - ._t.l_--~,-l-l-..-_ _.II_.____.-. -_^_ Reason for t!.Gs will be discussed latsr, Due to presence or absence of factor, loacted at position in complement other than chr. 9, required for chrr;:.ioser:e loss to occur: P&c @.&d;~vat~~. acttmfn h: p4~,.,#A,irr;!L l%!if\$ ,ots ^ -- shows the frequency of loss. I, 2.4. General conclusions: 4. Genetic fr,ctor, Ds, b). Mhen AC, to right of 'Yix in short arm of chro1~10sc1ne 9, another factor present, breaks occur at Ds. c), Breaks result in loss of all factors in s-:ort arm of chro"10so:>e 9 from Ds to the 8nd,3 d). Mhen AC absent, no breaks occur. Would not know Ds i>resent, e). ?!he break phenomenon at Ds compafable to mutation from recessive to dominant in general behavior battern, f), Two components in sgstem: the factor Ds, the locus sowing cl-ange, and AC, resnonsible for this change occurring -- controls the breaksc 1s. Next period: will discuss the cgtological evidence fox- breaks at the locus of Ds,