end lecture. January 11, 195h The discovery of Ds, Its behavior and its relation to mutable loci. I. Review of previous talk: 1, Sudden appearance of a large numb-r of newly arisen mutable genes --= expressing variegation-= in progeny derived from self=pollinations, 2, The origin in plants that had undergone the chromcesome type of breskace-fusion-bridge cycle in exnrly development. Healed broken ends of chromosome 9 in recovered branch, 3. The various types of plant characters showing variegation, arious types mentioned affecting hlorophyll expression, More types later affectin; other characters, , h, About lO different origins of mutability recognized in early experiment 5. The features shown by the seediing exhibiting variegation: a). Background - altered phenotyre, b). On background, streaks of normal vhenotype ec). The normal streaks present in a decided pattern, Reflect: (1) Time of change to normal during develonment of tissue -- determines the size of the streak (2) The number of streaks: reflects frequency of occurrence of changes to normal phenotype during development. (3) Ehe relative digtribution of streaks: reflect the distribution among a growing tissue in wnich changes occur in specific cells, (4): The different types of patterns: The Seedlings: Many later occurring changes Few late occurring “any early n changes, changes, +eaf [s a mosaic of many foe pas patterns. - \ j \ \ t if a. | po i . on | J 4 4 ad). Within a single progeny, one type of pattern usually predominant, 6. The changes in the pattern of mutations occurring during development. a). Sectors formed: tT). “nereased number of streaks 2). Decroased number of streaks 3). No streaks lL). Large mutant sector b). *he twin-sectors: One sector co-posed of two varts: rh t “yoes: 1). Normal phenotype: altered phenotype = no streaks . 2). " 7 " " - Ancrease or decrease in number of streaks, 3). No streaks : increased or decreased frequency of streaks. oe Lu). tnereased freauency of streaks: decreased frequency of , streaks, eritceerithenttlatesectors: Hach component of twin derived f ter cells, sectors arose from single cell as consequence of a mitotis,mxemk which produced two sister cells, 7. Interpretation of the nature of the change that occurred to give rise to single or twin sectors: a)e Particular pattern in seedling leaf reflects a controlled tyne of expression of@time when mutations will occur, andsthe ceils in which ther will occurah Povey - XkAt Ue dhY 1 Mase b). The factors responsible for this control may be altcred as a consequence of a mitotic event, ec). Following altereation, there will be a different pattern of rmtation in the descendent cells from that present before the change occurred, d). The twin sectors suggest that controlling factors segregate at a mitosis: one cell receives something that the sister cell lost, 8). “he mutant - altered pattern twin sectors: Suggest that the mutation itself is consequence of a mitotic event altering something, 8, The major questions and propositions? 1. What factor or factors are responsible for »roducing a artieuler pattern of mutations during development? i.e., (1) the tine during the develowment of a tissve when mutations will oceur, (2) The cells of the tissue in waich t-is will occur3 i.e., the frequency and distribution of e changes that will occur in particular cells during develooment, 2. How does the factor, or do the factors segregate in certain cells as the ccnsecuence of a mitotic event? 3. Is the process of mutation associzted with the same type of event? h, What component of the mitotic process is involved? a)e fs it a segreration of eytonlasmic cormonents? b). ~s it related to the chromosomes? ‘lo changes at svecific loci? c). +s it related to the process of chromosome reduplication? -3- II, the period of decision and t e early investisations,. 1, Original pvrupose, to analyse the genic components within the short arm of chromosome 9, 2. The presentation of a wholly unexpected phenomenon - the variegations, 3. Gradual conviction, following growing of thev ariegated plants -- that the phenomenon involved in the expression of variegation was far more invortant than that of the original purposes, stated above, l.. How could this phenomenon be investigated? a). At first, did not l:nowe b). As first step, decided to investigate inheritance behavior of a number of selected esses; and the inheritance aspects of the pattern controlling systems, “his in order to get facts with wich to think, 5. Pairst year and a half -- Results confirmed earlier observations, Showed that the alterations of phenotype were changes at the loows of a particular gene; a muyable gene, The change resulted in mutation from recessive to dominant. (wir). The control of the mutation process not well distinguished in early studies but suspected a similar tyve of change as that croducing mutation. III. The discovery of a variegation system that altored the chrsmosore QTD 2 Sa hicks be Orbe AUCLOL Turing development” “Ste nia jor mods” of operation: ai Sea a att te tne eaten Ll. Mkkherxakixer A part of short arm of d@rcosome 9 eliminated in certain cells during the development of a tissue, 24 The pattern of such losses in the various tissues simulsted the pattcrns produced by the mutable genes, where mutation from recessive to dominant occurs. Loss** oA Mutation: f ; was ret : fey ale hes . heyy i, vi \ | \ si a 5 x y wath PALES Sweet YE we i ' i i 3 The changes in patterns of loss, as seen in’ sectors, similar to the changes in mutation time and frequency noted with mutable loci: i . ‘ ; \ [ po / \ i V4 ;. ‘ f \ Ay | at \ \ 1 4 j \ ff \ \ j \ NH a \ py. \ f ; \ pry ‘ Hy | \ ji \ i i ae wa i i | 4 : } | { é i | ; | | | i i i 3 i ht r “ \ ‘ ° SARE \ » . \ aye “4 IV. How the system involving chrovosome loss was f s__recognizeds 1. First seen in some kernels derived from self-pollination of one plant that had undergone chr-mosome tyne of b.f.b. cycle in early development 2. “his plant -- carried two chrovosores 9 with newly hoaled broken ends, 3. The genetic factors carried by each chromosome: % yt 4 Ww I Sh Bz Wx ' “+4 ‘ 0 “eovsees WwW C Sh Bz wx n { eeovevenee lh. The factors carried in the short arm of chromosome 9 -= necessary to know them to continue study: W, ws Yg, yg. -- At end of short arm, I, GC, ¢ Sh, sh (a) Crossing over between markers Bz, b2 (b) Physical vositicn in chromosone Wx, WX ILLUSTRATIONS Cas 5. The pattern of variegation exhibited on some kernels of welf-pollinated ears ~ Lei Crh: Wt o xe, i oe nt. t . iy a ne La} ’ \ . . \ '‘ ‘ y ~ * — ‘ ens V. The structure of the maize kernel and its development, 1. Must understand this for any discussion of maize genetics or cyto-~ genetics. Will be given diagramatically for those woo are not familiar with the morphology and develovment of kernel, 2. The morphology of the mature kernel: (ILLUSTRATICNS « Cut kernels), View from embryo side qua‘ Cress section -=- longitudin NUM hy Ayako ® : : cy - “ * | a SN pee < . n oO 7 ag S . ‘ or ace | a a . Y he A, ; n abc c rz . : 5 | \ \ iy \ Ready th . i oy Kaggid Urey adlustustia: ' ~~ ™, "Nini ee Pa f * oy, 3) Gab Brows. 3. The origin of the endosperm and embryo in the kernel, a). “he ovule on ear, before fertilization: Ovule Meiotic mitoses Megaspore Megasporoevte + °% a n co if a ” LD) C> yo 2h — Sob \ i = . NU PREGGO OWE b). the development of the embryosacs: ¥ acwn. hee he The development of the male gametes: a). the young tassel, inside of leaves: telesrpoed effect, b). Composed of flowe.s along branches of tassel. c). Hach flower has three anthers. d). Inside anthers at young stage are enlarging cells = the microsporocytes. e). the meiotic mitoses and development of microspores: a ae ~ 7 | bts un 7 | 77 Whe EDOM ah a rset, eke. ate 8 ow, 4 bal a lug ah wf . Diedto le aut) ak trae aly 6). “he development of the pollen grain and sperm cells: a Poe AN | : Ye : if Apts - . f ate: Blike + . (yar - 5 UY . _ . . a YY -~ 64- 5S. the process of fertilization: Pollinations pollen tube; break into embryo sac The embryo and endosperm develope. Za golo, Vode - kam Bae Prue aM ome? bi WM rp x Wea oa VI, Return to case of chromosome loss variegation, The particular kernels 1. Assume femfle Cwx / C wx x male I Wx 2. Loss of I and Wx during develovment: Aréas of color in aleurone, Unde: lying areas, exactly corresponding, WX. : (vt 3e Cross section of kernel: kh. the pattern of such losses: a). Exceedingly uniform in some kernels with regard to @ ze and distribution of recessive spotse b). Not like pattern produced by otrer known mechanisms that result in losses of chrenosones: “he breakage-~fusion-bridge cycles Ring chromosome behevior, ¢)e Conclusion: A previously undiscovered mechanism at work here that produces the losses of I and Wx simultaneously. De Flants grown from the variegated kernels, Showed: a). White streaks on normal green background: VW AM C0101, b). segeges apncavad: no losses, increased or decrcasod frequency of > earlier ér Latér timing of Iosses. c). The twinesectors: No losses -- increased or decreased freq. of loss Altered pattern of losses in each sector: Uften increased in one and decreased in other, 6. Conchhsion: The mechani responsible for loss of mh romosome rete omer nce evn arb saa must be basically similar or the same as that prodicing @he gene mtations. a). *he "loss" corresponded to the gene mutation, recessive to dominant. b). The system controlling the time of loss, and the cells in wnich it will occur is the same trpe as that controlling when gene mutations will occur in the cases of the mutable genes. ec). Somatic segresatinns, occurring at a mitosis, of the factors associated with the controlling system occur during develorment and this results in altering the time and freacuency of losses in descendent cells, a). Some reciprocal relationship exists in the two sistcr cells resulting from this particular type of mitosis -- as if one cell gained something that the other cell lost. in cormarison with system present in the mother cell, 7. the summary s Comme risons between chr, loss and mutable loci: a)e Mutable loci: Mutation from recessive to dominant; Not chromosome LOSS. System present controlling when these mutations will occur, Controlling s stem altered as consequence of a mitotic event. Resulting two cells differe from mother cell, b). The chromosome loss phenmmenon’ Very same kind of mechsnism involved. Change occurs resulting in chromosome loss “ystem controlling when this will oceur “has system altered as consequence of mitotic event Resulting cells differ from mother cell with regard to this, ec), Something happens to chromosome to r sult in loss, What is it? d). the loss must be gross to include kekhx nearly all of short arm of chromosome 9. as seen in the sectors: Losses of W, I’ and Wx, 0). *herefore, this mechanism is. subject to microscopic examination, (1) Should be able to find evidence of t-is loss. (2)This has been accomplished, and will be described in detail d.ortly.e ce Y at -- 8. Genctic tests made to determine if Joss confined to particular chro vosome 9 derived from variegated plants. Seater HE a). Nature of test: | Female plants “ale plants . Rearranged chromosome 9 Rel oouee = Almost eliminates crossing over in short arm of chrom, 9, rw C ot © 7 Lou VO, o—-.-+—_—_-------— } + & nsw ol fv Cat Pa an \ b). Selected I Wx kernels with Cy areas - the var egated kernels. “ye ¢). Plants growm from them: constitutions: ad). hese plants crossed to (1) female plants carrying C (2) female plants carry ec 6). The tynes of kernels and frecuency of type on rem lting eas c& cross (1): Table 12 a (page 16) in Ac account. ll .ears gave 600 comletely colorless : 588 colorless, with spots of C : 1550 colored (C), _ Important: Only one-half of the i ~garrying chro..o someswere Warlegated, oo ieee ee f). +ypes of kernels on ear resulting from cross (2): toc With very few exceptions, ratio of 1 - colorless (I) : 1 colored, No regular trpe of © to ¢ variegation, f). Conclusions: 4 (1). Losses occur tn the chromosome derived from the variegated narent and not Ip the one derived from the tester planty 77 (2). Qnly helf of the kernels receiving the chromosome 9 from the original variegated plant showed these losses, Reason for this will be discussed later, Due to presence or absence of factor, loacted at position in complement other than chr. 9, recuired for chresosone loss to occur? Re \rv ackivet a . Acetate