Document 4QpMBkKky3oy5219aQ10654NV

VOL 240 NOVEMBER T7 W1 , nmrmmwrtry chromosomes in SB deficient hybrids ^ in a marked reduction in the extent of homoeologou* nB in pronounced contrast to the super high pairing that otturrwl in the itaence of 5*. _ . |t i Mean CKilim* Frequencies of F, Hybrids, with Supernumerary 1 CNomoiem*! and with r without Chromosome M a P* Pairing dasa SLeewraeUtiM ow) imennediete ( >ih) m Chromotome 51 Present * Absent * 0.9) (2) 3.27 0-4) 9.32 fI-63 16.30 <M> 0.91(2) 2.65 (2) 19.93 (0) , monoie Derhed from (he crones T. orri/mm aupkWd or mono-5Jx Ae- gi^lHHW^oS^n Owen ofelau ukan from Verdi end Dover4. a* gdity v*** Indeed the presence of supernumerary chromosomes created ineiotto t jfcanioo in which there wai compensation for (he absence of theee ^auwwnrnr SB of wheat. Similar effects of supernumerary PI ham ^emowmei on homoaolotous maiotk pairing have been pWt COtttB^orted in Lotiae*. Wtan 5B was abaeol (here was no dear segregation into UP both pairing oatagorire either in the preecnce or abeence of tad led itSmumermrics. Thu*, aggregation of dHCennt allelic con* j, arif^ioM al the two jv.'iing control led of Am. mntlea or At. (ybrtds to Mdrs Is only mM phcnotypically when SB is present juftmr, n*revv* ooMideralion of the origin of the control of the ^us,tt*PV*Mike meiolic chromosome pairing of polyploid wheat. ' dimmesome SB. had lad to the conclusion that the present rity of the BA locus may have arisen as a mult of mutation he time of. or soon after, the origin of (he polyploid'. (conclusion was reached because of the fkihire to detect, rg any of the dipioM relatives of wheat, a genetic effect nMing that performed by chromosome SB. AO the diploid _ types either foiled to compensate for the absence of SB Preventing homoeologous pairing, or they suppressed the t by which homoeologous pairing was normally pre* Previously these alternative effects were thought to specks, but the present and other results*'*'* a that the same genetic distinctions can occur within i. Oar present observations with standard chromosome aments of the two spedas, Ae. usuries and Ae. tpeltoidts, that the genotypes examined, which do not promote lotofous petring, could not have been the source of the ion exercised by SB in polyploid wheat. Moreover, in tiring hybrids, derived from the crosses T. oetthum ___ .____- uric 18* A*, flurries or A*. tpehoides, a bivalent was formed between the two 7M chromosomes present*. * he restriction of pairing in these hybrids applies only V taking place between homoeologous chromosomes to that between frill homoiogues, so that low pairing urety due to an asynaptk effect, is still no Indication of pre-existing genetic variation andard complements of diploid relatives of wheat that ire been the source of the BA allele. However, supery chromosome* of At. mutice and At. speUoides . t a gsnatic activity that limits homoeologous pairing, %Abiiag that of chromosome SB. The incorporation of a **** gagmen! of supernumerary chromosomal material, .. ^ by translocation, might, therefore, have given rise to it effect of chromosome 5B on meiotic pairing, tms based on the absence of meiotic pairing between wary chromosomes and 5B, and on the induction * Mirfrum fwVWtition in supemumeraty chromosomal material, Vg ebefrrenced against this idea. Nevertheless, only these hire''tntK have a swntlaT genetic activity to BA. Conte- tr cell et<*a [ . **'(*>r Hit* the question of the origin of the SB effect remains present work has added a third possible mode 'urther work will be needed to discriminate between 167 the three potential sources of B/i which are (i) the inclusion at the initiation of polyploidy of a standard chromosome- which has not been detected among contemporary diploids-- with an activity preventing homoeologous synapsis, (ii) ihc origin by mutation, in the polyploid, of an allele preventing homoeologous synapsis and (iii) the incorporation in 30 of supernumerary chromosome material ' Gabaiel A. Dovea Flam Breeding Institute, Merit Lane, Ttumplngton, Ralph Riliy ' Cambridge Received July 25,1971 ' Riley. R., and Kempanna, C, Heredity, It, 2*7 f|963). * Riley, R.,Ktmber,G.,and Chapman, \.,J.Htred.,$l,22 <1961). * Dover. G. A., and Riley, R., Ahunt New MMogy,23S, 61 (19721. * Verdi. A., and Dover, 0. A.. CVwmnwiw, 3g, 367 (1972). * Mochizuki, A., Jem, J. Genet., 39,356 (I960. * Evans, O. M., ana MaeefleM, A. J., Nature New Biology, 236,110 (1972). ,' Riley, R., and Law, C. N., Ad*. Genet., 13, $7 (1965). * KHntoer, G., end Athwat, R. S,, Frot. VS Nat. Arad Sri., 69 912 (1972). '' Critical By-products in the Synthesis of Polychlorobipbenyls Bunt samples of polycMorobiphenyls are desirable for toxicity tasting in preference to the randomly substituted products1 of commercial synthesis. Substrates required (by G. Denton) for specific teats with the American hardshelled dam Maetra mercenary were obtained by chlorination of N.N-diacetylbenridine1. This method has the advantage that the starting material can be obtained in a pure state and, following chlorination in acetic acid solution, the derivative (Fig. 1; X,Y~ NHAc, H) can be diazotized and reduced to tbe tetrachlorobiphenyt (Fig. 1; X, YJZ- H; Fig. 2, peak A) or further chlorinated by the Sandmeycr method to the bexachloro compound (Fig. 1; X.Y-G, 2**H; Fig. 2, peak B). The method has been used by a number of groups*, who have not, however, commented on the many by-products formed. Oas chromatography using an electron capture detector revealed eight significant components and seven minor products from the Sandmeyer reaction, while de amination of the rente starting material gave two major and and three other products (Fig. 2). None of these peaks was detected in laboratory solvents. We have been able to show that these complex mixtures arise from two known sidereactions which have not been detected before in PCB chemistry. Fig. I Outline formula for substrate preparation based on chlorinated N.N-diaeetylbentidine. In the first place N,N-diacetyl-3,5,3',5'-tetrachlornhen/idinc (Fig, 1; Jt\FNHAc, 2>H) is dcacetyiatcd to the mono acetyl compound (Fig. 1; A'NHAc, NNH., 2 H) in the conditions used for chlorination. This change is probably favoured by relief of strain induced by the rii-interactions of two chlorine atoms and the bulkier acetylamino substituent. In consequence the revealed amino group inertaxs the iclaiivc rate of chlorination of ring A. Evidence for this was found when one of the main products of the Sandmeyer reaction was MGNS 085509 i 1. \ ! ivaa 162 Pig. 2 OC separation of (he products of (e) reduc tion; (6) Sandmeyer reeclion with (<) Arodor 1234 U tempisle-'SO foot SCOT column, stationary phase `Apieton L' at 190* C. NATURE VOL 240 NOVEMBER 17 197? idanliflad as 2,3,4,5,3\4',5'-beptachlorobiphenyl (Fig. 1; X.YJ-O; Fig. 2, peak C) by NMR and maas spectroscopy. These methods ware also wad to identify two other new com pounds. Alumina (hexane) chromatography followed by recryaUilfxation (ethanol) was used wham preparative gas chromatopaphy was ineffective for the purification of 2,3,54', S'-pantachlorobipbenyl (Fig. 1; JT.y-H. 2-CI; Fig. 2. peak D) Dom the reduction, the formation of which ie forthar evidence of excessive chlorination. The isomeric 3,4,5,3',5'peatachlorobipheoyi (Fig. 1; JT.Z-H, Y-O; Fig. 2, peak ) was Isolated from the Sandmeyw reaction and dearly arises from competing reduction. Tbb reaction has bean demon strated4 during Sandmaysr reactions of the analogous 2,4,6trichlorobsnasne diaxoniua dsrivatims and under the condi tions of the Van Roosmako procedure1 both nitrotKt functions (of 1) may ha removed In this way. Thus 344/41' satrachloroWphanyl (peak AX a major product of raductioo, was also detected (by QQ as a minor component of the Sandmeyer synthesis, where the greeter number of products it to be expected, since comparing reduction of one or both diaso functions in symmetrically or unsymreetrically chlorinated precursors is possible. By using the OC of Arodor 1,254 as a template we have been able to identify other minor components in these mixtures from their retention indices1; for example 2,M,3',4',5'-hexacbloroMplwnyl (Fig. 1; X,Z-a, y-H; Fig. 2. peek P) and 2,3,A54/.5'-hexachlorobiphenyi (Fig. 1; JT-H, X^-Ci; Fig. 2, peak 0) were identified as reduction products during the Sandmeyer reaction. Ftall details of this correlation and of the spectre of the major components will he published elsewhere. It le possible that the extent of bi-product formation can be controlled, but not eliminated entirely, by adopting the con ditions used* for hindered anilines. Westfield College, Uninriity of London, Department of Chemistry, London NWi D. C. Avars Received June 23,1972. MONS 085510 * Sissons, D.end Welti, DChromatogreghy, 60,13 (1971). * Ven Ronmewn, F. L. W,, Arc. Trot cium., , 339 (1934). * HuUngsr, 0., Safe.S., end Zitko, V., Butt, fmin*. Comumim- ttom ToMteot., 6.209 (1971). * Melvae, 1., Sard. kyr. Ttdskr.. 92,404 (1971). "` H. H.,end Mehedeven, A. t.,J. Chem. See., 173 (1941). Eggshell Thinning and DDE Blue, Gish, Belisle and Frouty allege that DDE causes egg shell thinning fas brown pelicans and that the relationship is logarithmic1. In support of their cooclusinn that a cause and effect relationship between DDE and sheH thinning exists, they offer as evidence Wiemeyer and Porter's* work with kestrels. A critical review, however, shows that Wiemeyer and Porter have pot shown DDE causes shell thinning; on the contrary, the thinnest eggshells in both yean of that study were laid by the control group. The eontrd birds laid eggs with shells ranghtf in thickness from 130 tun-210 am in both yean, while rite DDE-treated birds laid eggs ranging in thickness from 163 tun-203 tun end 133 iuih1S3 ym for the respective yean of the study. Blus etal. also state that DDE levels reported in Wiemeyer sod Porter's experimental kestrels approximate environmental levels found in wild fakons. Such e claim b not borne out by CUde rf mi.* who have performed extensive tissue analysis, end a comparison shows that the levels in the experimental kestrels exceed levels accumulated In wild falcons by e factor of about two. Despite this, Wiemeyer and Porter only report mean shell thinning of9.7%, considerably kee then the 17% and 33% shell thinning reported by Hus ti at. In the South Caroline end California brown pelican colonics. To support their conclusions, the authors state that concentrations of residues in the female determine shell thickncae, a claim which is unreferenced, largely hypothetical, and without consideration of contra dictory experimental evidence. Blus et al. draw their conclusions from ststisticei analysis of egg residues and eggshells collected over two yean from three populations end two subspecies of brown pelicans and combine these to form one bivariate population. The authors assume,