MIR CORRELATION OF CYTOLOGICAL AND GHUINTICAL CROSSING-OVER T BRA MAYS. A CORROSORATION, By Unrviet 3, Creighton end Barbare UcClintook, Roteny Department, Cornell University. there has recently boen some skepticism expressed. (Srink: end Cooper, 1925) a0 to the value of the studies on the correlation of oytological and cenotionl crossing-over - in meise published by Creichton and MeClintock (1931) bedause of the formens of the date, since the paper by stern (1931)" dealing with Drogophiis ond heving much more extensive data appeared at vractically the same tine and yielded the gene conclusions, the cuthors felt it wmecessory to eda to the ever inereasing anownt of publishod work nerely to record more evidence of the sane nature without supplying anything essentiolly new or atvanoing. Therefore, confirmatory dante which have seaurulated since the tine the joint paper mentioned above was published heve not been considevet for « separate publication, However, we now feel forcell to cid moro date merely to counteract ony suspicion thet the evidence previously presented consti tuted ineufficicnt proof. This will be done in as brief a torn as possible, since ©. a@ircussion of the method hes been given in the peper mentioned above. Chromosome 9 in nmise is choreasterized by ite roletive g ise in the chromosone complenaat end by the 1:2 ratio in Lougths of its tivo arms e the ond of the s hort arn in sone strains possesses & lergo mob while other strains have & very enall imobd or no Imob. Evidence that the knob or knobleasas condition of a particular chromosome 9 is inherited with the same precision a5 a gene has been given in the previous peper end has been confirned in many addi tionsl croosese ‘The knob, therefore, sould be used as one eytologioal pavicer for this chromosene, The progenee | of on interchange deteen chronmosonos 6 and 9 (Surnhen, 1950, 1934; | LicClintock, 1950 " which broke chromosome 9 at a position on ~ the long orn o short distence avay fron the spindle fiber attoshnent region provided tho second eytological marker. Ghat the genes JZ, Ss Sh, wR" lie in the interohoncod chromesomextiich posecsscs the short arn of ance 9 has béen showm by UcClintock, 1931, Creichton, 1934, and. Rurnhan, 1934 " With reference to the Imob ond the 4ntorchange point, the order of the ceues ig Imobeyg-c-oh (surnhen, 1954). That there is very little erossing-over betiwocn the knob ond ye ean be seen “von the Gata civen belo. A plent with the constitution Imob-Yg-C~sgh-\ix- interchange veo erosseé to a plent with the constitution Knobdless-y6-S~ sh-wx-nornole the Fy wos beokerossed to Imobless-yg-G~sh~ weenormol. ‘Tyo hundred ond sixty one individuels resulting fron this becleross were omenined eytologically to to doternine the presence or absence of the mob (Imob or Imoblenosa in teble below) and the presence or absence of the intershonce (4nterehange or normal in table below) in the chromosome carrying these cones contributed by the F, perent. since there are five regions in which a crossover can bo detccted, the reaults heve been tebdulatoc nocording to crossovers wmioh ocourred in eaeh of these recions.. Tho tabulated reoults do not represent the totel backoross procery. A hicher percente ago of ¥r-G-Sh-% and yo-o~gh-tm plents were axenined eytolocically in en offort to obteain crossovers betweon the knob and yee Likewise, more Ye plants were cxanined eytologically than ye, since plents honosygous for ye cre reduced in visor ond often do not afford ovfficient natericl for oytolo;icel examination. DADLE 1. Knob besee¥ $ ol} - She’ ime $12 to re hez L¢ "e Tema ly ’ TP oe CS ne SUEY ee VLE F2 rnal Pi Sane DLO BB is c sh VI OF bed umber of individuole. Noneerosoovers 1, FnobeYoeCeShezeinterenriye of £,Knoblese-yoeoe-sh-wxenornel EO Srcescovers in recion l. 5. Enob-yc-cesheteenornal o 4, Knoblcss-Yo-0 -dheimeinterchrenge 1 Crosoovers in region c. 5S, KnobeYo-c-shewa-nornel 135 6, Knobless-yr-C -Sh-VWz~-inte: change 11 Crogsovers in region 3. 7, Knob-Ye-C~oh-rax-nornal 5 &, Knobdlesseye-c-Sh-le~-intorchenco o Crossovers in region 4. 9, Knob-¥e-C-Sh-mmenorneal 55 10, Knobloss-ye-c-sh-¥x-interchenre 168 Crossovers in region 5. 11. KnobeYg¢-C -Sh-"m-nornel 16 12. Knoblesse-ye-c~-chewzs-intorehence 3 Dovdle exrcssover involving regions 2 and 4 13, Knoblesseyg-C -Shewzenornel 1 Pouble crossovers involving reriozs 4 and 5, 14, KnobeYeC therein terchenge 15. Knoblesseyo-c-shelix-nornel ng tn It is obvious from the date given above that e ceretic erossing-over betycen the genes Yg-C~Sh-e~involves a cytological crossover beteen the Imob cna the interchange pointe There data, therefore, supplenent those given in ovr previoug .ublicction and in@ieate the soundness of the conelvsions drermm,. The gonep refored to in thia paper by symbds cre: ye, yellove ereen plents; o, colored elourone, sh, shrunken ondosperns Wk, vwexy endosperm to m Lirink, RA. ond Cooper, C.D., Goroticg 20, 22-55 (1955). Burnhen, C.R., these frocecdings 16: 269-277 (1920). " non Genetics 19:4508447 (1954) i! vw OH ADs. Het.68; 81-62 (1954). Creighton, H.3., these vroccedings 20: 121-115 (1054). Creighton, H.3.and MeClintock, Be, these Prroecedings 17: A92-497 (1931). NeClintook, Be, these Froccedings,16: 791-796 (1950). SvoCLintook, 3e, these Proecedings 17: 405-491 (1931). stern, Ce, Biol. Zbl. 51: 547-587 (1951),