Lecture 7, January 28, 195k 4 Continuation of transnosition of Ac;and its reletion to somatic sectoring and to controls of mutaticn of mutable genes. I. Review of previous discussion? 1.in all major respects, Ac is inhcrited as a mendelian unit: a). Expected statistical ratio in Fo, ZB Ac : 1 acs found, b). Expected § "in bee. of Ac/ac: 1 : L; fornd, 2. When)homozygote, Ac/Ac, backcrossed by ac, some unexpected events revealed: a). Not all of the plants carry Ae -- few with no Ac b). Others, 2 Ac factors, independently located \ We + Re ce), Alteration in action of Ac twncurtd: a“ (1) Dosage action of single Ac double that of original Ac = Re ke (2) Dosage action of single Ac increased over that of original Ac but not double that of it, (3) Dosage action decreased, Ds breaks occur earlyer in develovment of tissue than those occurring when oripinal was present, 3. The changes in Ac occur late in development of the sporogenous tissues: (1) This show by the scattered kernels on ear that carry the changed Ac factors. Rr - (2) In ease presented, these changes occurred in only a few of the ovules produced by the female plants. II, What is the mechanism responsible for these changes of Ac? 1. If one Ac transposed from one chromosome to another in sporogenous cell, before meiosis, could get either no Ac or 2 Ac in the resulting spore or gamete: . he as a fre wee Sy pak Ui: Re A Re Rc. ~ Ws ah wo omar Vooment ati Oe oo Ws aeturn rs ated | 2. If one Ac in on chromescne romains in one chromosome after chromosoe reguplicaticn, can cet double-dose Ac or no Ac: wok at © kh ee | apna, wet 4 Ne \ ul 6 In develooment of the megaspore, either of these two cells recovered but not both: Only one cell develops into the megasroré, and onely one of spores produces the female gametorvhyte: IIi. 1. Mk ch _ Rei one Be | ’ f a, oko a ee he ‘Ny he \\ __ YO ite 3e In either case, world excec: to Pind a 1: 1 ratio of kernels with no Ac to those with either 2 Ac or double-dose Ae, 7o Observed: 19 with no Ac to 23 with either 2 Ac orjAcdc . kh. In addition, Ac was found to change in action-~ to increase its dosage action or to decrecse it, How does this occur? If it is transposed, does its ositicn affect its action? “wp: If changes occur of this type, without change in position, is Ac composed of a number of sub-units? Cr, is its efficiency in scme manner abtered? What evidence have we that Ac does move from one ositicn to another in the chromosomal com lLement? Lo study, sho: 1d kmow the position of Ac in the chromosome com lement and study is changes at this position and its removal from this positi n, This was done because of appesrance of Ac in chromosome 9, which is well marked, The first discovered case of Ac Appearance in chromosome 9: eo a). In cross of ac/ac plant by Ac/ac plant, no evidence found for any A\linkace of Ac with markers in chromosome 9. pee b). The Fj ‘carrving Ac grown, 9 plants erossed to plants not carzvying Ac, A 7 Both chromosomes 9 in male parents with Ac carried genetic markers in chromosome 9, ec). 8 plants showed that Ac was not linked to factors in chromosove 9, d). 1 plantz the Ac in this plant linked to markers in chr. 9, e), its position tested, Found to be located to right of Wx: G Wx Dg Ac f). Type of data obtained in test of linked and non-linked Ac: C sh bz wx ds, ac female by Is: I Sh Bz Wx Ds Ac male ‘“\ Sh Bz wx Ds ac IT: I Sh Bs Wx Ds Ac CG Sh Bz wx Ds ac Table 1, page 23, Symposium paper, ® 2. Later, other cases of apnvearance of Ac in chromosome 9 found. One of them, Ac in short arm, just to left of Wx: Cc Ac Wx Ds a). Example of how such a case discovered: Number of slants in a culture came from one in wich Ac had not ,been located in chromosome 9, these plants tested for Ac. One among them may now show Ac in chromosome 93: the test type: Eyewpee Female: _c Wx Ac x C wx Ds, ac male: C WX ac Kernels on resuting ear: Would syyet 1 C Wx, nonsyeriegatod : 1 & Wx, with areas of ¢ Wx 1 C wx, non-variegated : 1 C wx, with aveas of c 3 3 Wo We Re lr female ec Ac W male wer Se x C wx Ds ae, then, modified c ac wx ratios of variegated to non-variegated expected in Wx and wx classes: The exbent of deviation from 1: 1 would depend upon how close Ac were to Wx, And, the frequency of transposition of Ac from chromosoze 5 position, as indicatcd, to another position, Example in one test: C Wx calss C wx class Non-var, CWx-cwx var Non-var, Cwx with ¢ areas 19 207 16h 1h b). Ac obviously closely linked to x, The order could be: (1) or (2) c Ac Wx ec Wx Ac Cc ac Wx c wx ac >). In usualy genetic test, it would be simple to locate factor by a three=point test: C Ac Wx C Wx Ac Cc ac .WwWx Cc Wx ac i" Befetmine the vosition and crossover frecuencies readily in inmost " genetic tests, va his not easy in the case of Ac, this is because of transpositions, d). A number of different tests conducted with tuis case, It took nearly three years before location and cross-over frequencies covld be stated with some certainty. 6). Tests are tedious to describe and not easy to follow because of number of genetic markers used; and the many typespf tests made, f). To avoidé such descriptions, a relatively simple type of test can be used to illustrate what happend: 4+he cross: female male (1) c ac wx ds y C ac fwx!Ds ce ac (wx) ds C Ac ‘wxids (2) Type of kernels on the resulting ear: “heir constitutions as expected: non-crossovert cross-over 4.78 Colored, non-variegsted | C ac Ds « GAc_ds Cac Ds c as ds c ac ds ec ac ds 17 Colored with c areas C Ac Ds c ac ds (3) 17 "crossover" carrying kernels selected from ear. Plants grown from them, 16 plants testeds one died, Eachrphent .¢rosesdobyy 1 Wx Ds ac " " " to c wx ds ac The results: 13 plants of 16 only, as records of other 3 not heres ~ 7 6 plants were crossover types: ¢ Ac wx Ds e ac (wx)ds 6 plants had Ac, but not in chromosome 9 short arm C ac(wx) Ds Ac . ¢ ac (wx)ds ac \ 7 | Gh 1 plant had no Ac, [Taw pcobeay va mbps rode ow om 01h (4). This test shows that only half of the appawent crossovers are true crossovers. The rest carry an Ac, not in chromosome 9 short arm, lh. Other cases of appearance of Ac in short arm of chromosome 9: Ac ¢ Wx &). Changes in Ac that were observed: Disapvearance from short arm coincident with apnearance elsewne re, Change in dosage actions Increased or decreased, either with or without change in location, \ +: Aa Z 4 . 4 re yet Raa VAR, rhe ay Wyo - 5. A correlation noted between changes in location, and/or action of Ac and changes occurring at Ds, he coincidence rete is high. a). This has made it vossible for ready selections of changes in location of Ac in kernels carrying them Will be discussed later, where this will be strikingly avnarent, IV, With evidence of changes that occur to Ae in mind, it is possible to evaluate the pattcrns produced in kermels carrying Ds and Ac, 1. The "early sectorials", Changes of Ac occur very early in development of kernel, Result in sectors SOW DE different types of Ac action: these apnear in kernels carrying two 4c or a double-dose Ac, Female with Ac . Male with dcvubedose Ac C sh bz wx ds Ac x male I Sh Bz Wx Ds C sh bz wx ds m I_etecDs no &c ac AgAc The endosperms: “he endosperms: 2 indenendent Ac 1 AcAec “~~ 2. One of the AcAc males (homo%ygous and allelic positions) crossed to various tester plants as females, 90 - 95 % of kernels wee early sectorials: C(C% 4 : . it . roy a 2A ae The 3 most freauent types: We whe 4 ake io @ é 4 oY ho fee 4 he T ~ nfh- Weel -T7- The infrequent types: oa ah ihe @ 3. Other cases, from crosses with female introducing Ac, Some isolates give sectoring later in develonment: Examples: Pade) we h, With this in mind, can attermt to evaluate the patterns observed when 1 Ac present, Examples s a). The kernels are mosaics of adifferent Ac constitutions: No Ac -- not Ds breaks; sectors not sowing breaks sub “ittihin them,/sectors produced with no Ds breaks or later occuring Ds breaks, Mah 6) 2 Ac = sectors produced with Late occurring Ds breaks b). Pattern of variegation in the kernels receiving 1 Ac reflects the changes occurring to Ac and the time of these changes. It is not a "chance" pattern of Ds breaks, Wp - ¢)] Different isolates of Ac can show quite different patterns in 1 dose, (1) With some, changes in Ac commence early in the development of the endosperm, (2) With others, these occur much later, (3) the ccnsequence: Various t pes of patterns produced by different Ac isoletes, These different actions reflect differences in the Ae factors These differences have been designated different "states" of A Ce concaaae mnie ane ~~" ", The bearing of the Ac investigation on the problem of what is operating to control the mtations at the locus of the mutable SeNneSe 1. In the first discussion of this series, the reasons for undertaking the study of mutable loci were emphasized, 2, It was emphasized that in all examined cases, and there were many, -~ a controlling system was present, This system controlled the time of occurrence of mutations during the develonment of a tissue and the cells in which it would occur, -5.- (5). Whe-e did this Ac come from? If we assume transposition from short arm of chromosome 9 to another chromosome, this situation covld be explained: Spotggenous cell a), C Ac ds C ac Ds @eeeevsces ee ee | ~ ’ . homologues homologues of another chromosome b). Ac transposed in this cell to ........ chromosome: CG ac ds C ac Dg eckGesece @veveccerce ¢). “eiotic segregations: Segregations: Synapsis: C de ds cece eeee C ac ds ee. ac 7} ———— FFHORCCH OCS CG ac Ds re ee ee ee Ac . > C ac Ds cece cece (6). In the described test, in selecting for supposed crossovers, ss we are also selecting for transpositions of Ds, Such were oD present in approximately one-half of the suprosedly cross-over class, wy) —j 3 le can also test for the removal of Ac from chro-osoue 9 siort arm: ¥ a). Exam-le of the type of test: Fenale Male ec Ac % C Ds ac c Ac C Ds ac Types of kernels on ear from one such test: (Most of tests not here) 3 kernels did not germinate 6 ©, non-variegated: 3 remaining plants tested: 168 C with ¢ areas: 2 had no Ac . Tee ¥ 1 had AcAc but no change in locati 2 kernels with very = ~ ~ “ late speckled Plant grown from one of two kernels: pattscr of losses, ( Ac not in chrozzosome 9, Plant Wass 6 Ds Ac c ds “ac Ac action altered from that snown wnen in chr. 9, 3. The observations for these conclusions came from the appearance of "twin sectors", They were: /~ \ Piva lh. Thase relationships within the twin sugsested that one cell received something that the other cell lost, and this something was associated with the control of mutations in future development -- in the wip —é cells arising from those where the changes occurred, 5. Since twin sectors apnesr to come from sister cells, the event anneared to be associated with the mitotic PPOCESS, 6. Also, the mutation process itself anneored to occur during a mitosis, and this often correlated with a change in the controlling svstem: * % ~~ Ac controls bhe occurrence of breaks at Ds, If these events at Dg are compared to the mutations at mutable loci, then parallels may be drawn; Ac is the controlling system controlling the "mutaticns" in this cease, a). Segregaticns of Ae occur at somatic mitosis, One cell can gain an Ac that the other cell loses. Resubt is an altered time of Occurrence or the absence of occurrence of Ds breaks in the progeny of the two resulting cells: b). The concident changes at both Ac and Ds: these frequent. Result in sister cells, one of which may have altered Ac: Change in Ac in sector with Ds break oe / co eS 7 oe Sesulting sector: vy — Wwe Utedo 4} ALY Lu Lut Thee . 4 toa te tha Pee ty tek 4 is Lo foulh ae mitted fatty. Bebe! ce). The parallel regarding controlling systems is striking. This would suggest that the muisble genes also have controlling units that ae resnonsible for the patterns of mutaticns, These units either at the locus concerned or are separate - as with Ac, VI. In next discussion, wovld like to consider Ds again and snow that it, also, transposesfbomone location to another and that there are very strkking consequences produced as a result of this; It is the cause of the a-mearance of some of the mutable genes,