I OFI ORNL P 3077 EEEFEEEE 11:25 .4 .5 humm EAN.LAL, MICROCOPY RESOLUTION TEST CHART NATIONAL QUREAU OF STANDARDS - 1963 . .. 14 N . * ** 12 ORNV-A3007 Conf.67.0525--1 HASTE WIN 1 3 1957 For International Atomic Energy Agency Study Group on "The effects of radiations on meiosis" CESTI BRICSS · . . . . . -. . . ... Ha 12.00 MN-65 . .. A survey of methods for the induction of aberrations in meiotic stages in Drosophila females and for observation of their disjunctional properties in the ensuing meiotic divisions* D. R. Parker Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee and Department of Life Sciences, University of California, Riverside -- - - LEGAL NOTICE The report was prepared as an accout of Government sponsored work. Neither the United ..:... Statne, nor the Commission, nor any person acting on behalf of the Commission: A. Makou may warranty or representation, expressed or implied, with respect to the accu- rioy, completanou, or usefuaour of the information contained in the report, or that the we * of may information, appartto, method, or process dinsloned to me report may not latriage privately owned rightes or B. Asmmat any liabilitas with respot to the use of, or for danacor renulting from the :.: į um of my taformation, appertue, wethod, or prooen drclorad la tie raport. As wood in the above, "pornou hotting on behalf of the Commission" laclades say on- :: ..: plonne or contractor of the Commission, or employw of such contractor, to the extent that med employw or contractor of the Commission, or employee of mooh contractor propurus, dorminatot, or provides ncotu to, may information pureunt to wo esployment or coatrict with the Commission, or M. omployment with mucha contractor, . * Research jointly sponsored by the Department of Life Sciences, üniversity of California, Riverside and the U. 8. Atomic Energy Commission under contract with the Union Carbide Corporation. .? : ...::: . :. . : .* : --- . AN N DISTRIBUTION DE CHUS ORCIMIESON . ONLINMATES P i ........ ... Running head: Drosophila Methods Send proof to: D. R. Parker . . . . Department of Life Sciences University of California Riverside, California 92502 USA . (after July 1, 1967) " V.. . . .:.:.::. :. - ., : .:.: . i 3 ...... . . ..: The effects of radiations on cells undergoing meiosis may be approached from two distinct points of view: that of measuring the extent of the genetic damage ofTooted, especially wit may relate to human damage, and that of utilizing radiations to better understand the conditions and mechanisms of meiosis. Radiations provide useful means for disturbing meiotic processes, hence for gaining insight into those processes. In turn, this may help in the analysis of genetic damage and give fuller understanding of stage sensitivity differences. . The genetic effects of radiations on meiotic stages in Drosophila have: been studied primarily in the female (Abrahamson, Herskowitz and Muller, 1956; Parker, 1954, 1963). This has üven due in part to the simpler problems of sampling in this sex, and in part to the consideration that, for man, radiation effects on meiosis, in the main, have to do with the female, those on mitosis with the male. However, Drosophila 18 deficient in one important respect: female meiosis 18 not entirely amenable to the usual cytological approaches. The Drosophila worker may wish to think in terms of the course of meiosis as described for other organisms, remembering there is no assurance how similar. the Drosophila situation may be. Techniques have been developed for studying aberrations Induced in females; some of these might be adapted for use with irradiated spermatocytes, although the more difficult problems of sampling limit the usefulness of the male. . . :. - - - - - - -- - - - . . . . W wwmov. . . .... . Interest in radiation effects on oocytes centered initially on questions of differential sensitivity, and use was made of conventional methods of : screening for gene mutation (e.g., recessive lethalo) and age hatchability (dominant lethals). Procedures for these are well known and need not be repeated here; the main technical problem 18 tinat of obtaining homogeneous samples of well-identified stages, and that will be discussed below. As we learn more about the nature of the genetic events that are induced and can be detected; it is not found possible to express sensitivity differences in quantitative terms only; qualitative changes also occur. Comparisons of stages become meaningful only in terms of the entire spectrum of genetic damage, for relative sensitivity may differ markedly depending on how damage is detected, and in some cases on the specific chromosomes involved (Parker, 1963). Recent work has dealt with induced exchange, especially between non-homologous chromosome 3 (Parker, 1965, 1967). Methods suitable for detecting aberrátions ::: induced in sperm, looking for reciprocal translocations for example, have at best been disappointing when tried with the female. The conditions of meiosis must be kept in mind in designing experiments to study the processes of induction » and recovery of aberrations induced during meiotic prophase. For the detection of an aberration requires that there be a set of conditions and processes, allowing the aberration to be formed, to pass through the neiotic divisions and be incorporated in the egg nucleus, and finally allowing the zygote to develop into a viable, fertile, genetically analyzable individual. . t .. 1 h .vet . . ... :..", . '.: - .:: . : =;:;:..sins .. As methods of screening for aberrations are developed, one may ask an increasing variety of questions about radiation-induced breakage and rejoining of chromosomes, and about the behavior of newly-induced aberrations in the ensuing meiotic divisions, and how these may be related to the more crudely. assayed differences in sensitivity observed in earlier experiments. How are sensitivity differences related to chromosome breakage and its repair? : How does nuclear topology affect the ways chromosomes rejoin or restitute? And what is the relationship of the newly-formed aberration to the processes of disjunction? The'i variety of especially constructed chromosomes available in e Drosophila permit ihe synthesis of special purpose stocks for use in answering these questions. Hence, a major role for Drosophila in the study of radiation ......... effects on meiosis sbould be that of defining problems. It is the objective of this survey of methods to recount a few ways this can be done. New techniques must be devised as we learn to ask more sharply defined questions. .. . .::. .:. Samling Obtaining identifiable meiotic stages is possible in the case of the female, since the meiotic divisions do not occur until after the oocyte 18 laid, and . .... meiotic prophase extends over a period of approximately one week's duration. . · It is possible to obtain fairly uniform samples of a single stage by limiting the period of egg collection so that not more than one oocyte is recovered from each ovariole. On the other hand, in the male, meiosis occurs long before the completion of sperm development and the insemination of the female, and at best one can distinguish meiotic stages from pre- and post-meiotic ones, with little hope of subdividing the various stages of development of the spermatocyte.: JU . i .. :. Il According to Bucher (1957) the first primary oocytes appear in the basal portion of the newly-formed germaria about nine hours after the beginning of the pupal stage, although this time may vary according to the stock used. Until this period, only mitotic divisions have occurred in the germ ceils. Proliferation of the germ cells in the ovary begins during late embryonic :: development, Increasing the numbers of oogonia in the developin 8 ovary. In Bucher's material, at about seven hours after the beginning of pupation, the first synchronous divisions occur. Pour divisions of a single oogonium (cystoblast) lead to the formation of an inter-connected group (cyst) of 16 cells, and the last three of these divisions are synchronous, the only ! synchronous divisions encountered in this material. Fifteen of each cluster of 16 cells are nurse cells; the remaining one being the primary oocyte. Finding in the ovary clusters of eight cella in simultaneous mitosis tells one that ........... .. . .-. : .: : ..... . . of nurse cell and oocyte nuclei proceeds and these can be distinguished by the larger size, higher DNA content, and the active RNA synthesis in the former (Guyenot and Naville, 1933; Painter and Reindorp, 1939; Jacob and Sirlin, 1959; .... . . ....: should check his own material to determine when primary oocytes first appear. Following the formation of the ovarioles and the differentiation of the germarial oogonia into 16-cell clusters, further proliferation is by spical cells located at the anterior ends of the germaria. Models of proliferation by stem cells have been developed and discussed by Koch and King (1966), who prefer a model , -... .... . 1 . - 1 - - - At about 48 hours of pupal development in Bucher's material the first follicles are formed, marking the beginning of the formation of the vitellarium. Koch and King find that the ovariole in the young, newly eclosed female has about seven 16-cell clusters 'in the germarium and a similar number of follicles in the vitellarium. They estimate that it requires about three days for a 1.6-cell cluster to pass through the germarium and another three days through the vitellarium. Oocytes beginning the meiotic process at the time of eclosion might be laid at the earliest approximately six days later. This is in reasonable agreement with the earliest recovery of labeled eggs by Grell and Chandley (1965) following injection of tritiated thymidine into females. Radiation studies to date have largely been restricted to older stages of oocytes in the vitellarium. King, Rubinson and Smith (1956) have described the structure of the ovariole in the adult female, and have designated 14 developmental stages of the oocyte. They recognize three sensitivity groups on the basis of recessive lethal mutation, X chromosome losses, and dominant lethal effects. However, much of the work of others has been concerned with but two of the stages they desodbe, stages 7 and 14 ( Parker, 1963), which are, respectively, the oldest stages in newly emerged females and the fully :::. mature, chorionated oocyte found in females ready to begin egg laying (usually during the second day of adult life.) Commonly, one irradiates virgin females either within a few hours of eclosion (e.g., 12 hours) for stage 7, or after aging 3-6 days for stage 14. Treated newly-emerged females are held in uncrowded food containers for 24... to 48 hours before mating; aged females may be mated immediately after being irradiated. To guarantee sample homogeneity, each investigator should verify . - - , " E - - . .. - - - . .- .- - -. for his own materials and methods that the maximm number of eggs the female is permitted to lay does not exceed the total number of ovarioles in her two ovariu. When females are actively laying, a period of 12 hours uually gives a reasonably homogeneous sample. Actively dividing oocytes have received attention by Ulrich and associates (Würgler et al., 1963), whose method is to irradiate the oocyte shortly after it is laid. They find that well-fed flies, that are protected against shaking and variations in light and temperature begin egg laying promptly after; insemination. Oocytes are in Metaphase I at løying, and after about 2:5 1.5 minutes about 92% are in Anaphase I, the remainder being in later stages, due to the occasional retention in the reproductive tract of the female of an egg after it has been inseminated. Anaphase II occurs at about 10 minutes afterlaying, syngamy at about 16-17 minutes. Sensitivity varies widely over these stages, with stage 14 and the division - stages being much more sensitive than 18 stage 7. With stage 7 a reasonable number of cells will survive after doses as great as 6000 r or higher, while the most efficiently used dose range for stage 14 and the division stages , 18 well below 1000 r, 500 r and lower being commonly used. -. - .- t - . - Detection of Aberrations, Attempts at the recovery of reciprocal translocations from irradiated Drosophila females have been almost wiformly mouccessful. On the other hand, where the effects of aneuploidy are not great, it has been possible to recover one of the two products of exchange between two chromosomes. Excluding "induced crossing over" between homologues, these "hall translocations"; as some workers call them have been found as detachments of attached-X chromosomes and as fragments of Y chromosomes. Hore recently, in this laboratory t hus been possible to induce and recover parts of reciprocal translocations between major autosomes. Until suitable screening methods for any given kind of aberration have been worked out, it is not possible to choose between the alternatives that the event is not detected because it does not occur or that it is not detected because it does not survive due to aneuploidy, or etc. Answering of these questions also requires some degree of genetic analysis of the aberrations recovered. 1. Detachment of Attached X. When attached-X females are irradiated, there .... 18 a dose-dependent breakdowa of the attached X's, so that egg nuclei having ... single X's may be recovered. This is recognized by a breakdown of the usual pattern of production of matroclinous females and patroclinous males. While the details vary considerably according to the experimental objectives, the . usual procedure is to cross the attached-X females, marked with recessives such as yellow vermilion bobbed (y v bb), to males having a multiply-inverted balancer X, such as Muller-5 or 1-6, marked with the dominant, Bar (B). In such a cross, the detachment individuals are recognized as yellow vermilion males and heterozygous Bar females. In this laboratory, woually the markers for the first steps in genetic analysis are introduced in this first crou. ... .'. : ' • . i.. . Use of the balancer X allows one to keep the detachment intact in the heterozygous females, and to establish it in stock for further testing. Stocks are usually established by crossing detachment-carrying males to : appropriate compound-X females. Attached X "detachments" have been found to involve exchanges between X and Y, X and 4, X and tips of major autosomes, or gross deletion of an X from the attached X. Tests for each of these may be devised; in some cases the tests one wishes to use may influence the choice of markers in the attached v ... e re, L. MANUS X-Y Exchange. Analysis of this class of detachment 18 facilitated by using marked Y chromosomes; a number of these are available with single markers, or doubly marked. Some doubly marked have different markers on either arm, others are 180-marked. In these cases, exchange with the Y 18 detected first by linkage of a Y marker with the detachment. More detailed analysis of these i detachments is made possible by testing for the presence of male-fertility genes located in the Y. Por male fertility, a complete complement of Y-linked fertility genes is necessary. Tests for some or all of these may be made by: :. crossing detachment-carrying males to attached-X females that have no free Y, or have some kova tester partial Y. If the detachment-X 18 complemented by the partial Y from the female – 1.0., 11 the sons are fertile - it can be concluded that the loci missing from the partial X must be present in the detachmeät. Thus, it is possible to determine which loci are present, which are missing, and : where on the map of the Y the break-point falls. These partial ris used in .. . ...'.;. . :: . . : .... . . testing carry markers (e.g., yellowt), and it is wise to follow marker , segregation in these tests to verify that male fertility to due to complementation, not due to non-diojmotion giving males an extra y that would be unsuspected were it not for aberrant marker segregation. In some cases, the tester Y's may be "leaky", that is the deficient Y may allow a very low level of fertility. This difficulty may be obviated by making tests of individual males. In this laboratory a usual practice is to make mass matings, followed by individual matings of males from each fertile mass mating. X-4 Exchange. Tests for X-4 linkage may be made by crossing detachment- carrying males to compound x females homozygous. for fourth chromosome markers, such as eyeless (ey) or poliert (pol), and backcrossing F, sons to similar females. Two situations may be found, when there is linkage of X and fourth chromosome markers. Males will not show the fourth chromosome markers in either case; where the detachment-carrying flies are hyperploid (1.e., have a free maternal fourth chromosome in addition to the detachment), some females show the marker phenotype, others do not. Where the detachent-carrying flies are hypoploid (1.e., deficient for 41, and having no free maternal fourth), all females will show the fourth chromosome marker phenotype. Recently a speical stock has been made, making use of a small duplication carrying the normal allele of yellow (y*) attached to 4L. This enables one to detect detachments that are capped by 4L, for these will now have it linked with the detachment. .. .. ....... . . . .. • • ... . X-deletion. Großs deletion of the x leaves a "detachment" capped by the tip of XL. If the attached X 18 heterozygous for distal markers, one may, then find single X's carrying distal markers from both X's. While this: system makes analysis simple, its deficiency is that it cannot detect cases where it is the sister rather than the homologue that supplies the cap. We have used attached' X's marked by the darker allele of yellow, yellow. We then make the detachment heterozygous with an X with the centromere end marked with yellow, and with the mutant yellow in the normal positioa. If the crossovers of the appropriate type are yellow?, rather than yellow, there must be a cap carrying the mutant, yellow, which means the "detachment" arose by two breaks in the X. Alternatively, one could look for linkage of the normal allele of lethal (1) Jl. . . . X-Major Autosome Exchange. For exchanges of this type to he recoverable, the break in the autosome must be near the end of the chromosome. Tests for X-2 or X-3 exchanges are similar to those for fourth chromosome involvement, using compound X females with markers near either end of the major autosome, These exchanges differ from the X-4 exchanges in that the expected hypoploid class must always be a "captured" rather than a "capped" detachment, 1.6., must have an autosomal centromere. In this case, detachment carrying flies will be deficient for one end marker. Expectations for the hyperploid are similar to those for X-4 exchange, the detachment being capped by a chromosome : end carrying the normal alléle of one of the markers. ITU :: :.:.: *..* . . :.::.:. :.. from ordinary attached X's (Reversed Metscentric Compound X'S = RM) by having the centromere at the end rather than between the two X's. There has been little use made of detachment of RA's (Parker and Hammond, 1958), although they offer one distinct advantage in the lack of ambiguity in localizing break points. One usually recovers the proximal X as the detachment, hence there is no doubt as to the origin of the centromere, nor where relative to the centromere the break occurred in the chromosome exchanging with the ................ RA. ............... .... 3. 1 Chromosome Fragments. Another useful type of "half translocation" is. the partial Y chromosome, derived by exchanges either within the y or between the Y and another chromosome, frequently the fourth. Detection of these rearrangements is facilitated by the use of a doubly-marked Y chromosome, such as the Boyy (Brosseau, 1959). Females carrying attached-X chromosomes marked with yellow and carrying the doubly-marked Y are Irradiated in the chromosome, likewise desired manner and mated with males carrying an attached-XY /allows recovery marked with yellow, and no free Y. Use of the attached-XYT of partial Y chromosomes in fertile males; recovery over an ordinary X would ..... ...... result in sterility in the majority of cases. Exceptional flies, i.e., those - - - - - - showing loss of only one of the Y markers but not detachment of the attached X, are saved from the progeny and used in establishing stocks. Exceptions may occur in either sex, though more frequently usually among the males. It has been found that there is a difference in the array of fragment types in the . . . .• . . ...... V .... ........ . .. . 1, To be able to maintain the stocks, i.e., for males to be fertile, it 18 * necessary for males to carry attached-XY chromosomes at least through the early stages of fragment identification. Exceptional males may be crossed to attached-X females carrying no free Y; exceptional females to attached-XY/O males. In some tests it is convenient to cross males to homozygous attached-XY""females; this has the advantage of keeping the fragment in the male and avoiding the necessity for virgin-taking in each individual test-cross. The two principal types of fragments so far found arise either by : exchange with chromosome 4, or by a non-reciprocal exchange between the two y arms. Other types of exchange are still being sought. Testing procedures for fragments are somewhat similar to those for detachments, : differing mainly in that males carrying fragments are crossed to females carrying free X's (free attached-XY's) rather than attached X's. This serves the same purpose of keeping the tested chromosome in the male. : Y-4 exchange. Attached-XY males carrying the partial Y are crossed to homozygous attached-XY females homozygous for fourth chromosome markers, and the F, sons are backcrossed to similar females. Linkage of 4R with the retained Y marker is recognized by failure of males to show the fourth- chromosome mutant phenotype. Again, these aberrations may be recovered in individuals either byperploid or hypoploid for a part of chromosome 4 – 1.e., with or without a free maternal fourth chromosome in addition to the right arma of 4 now incorporated in the fragment. The former type will show two phenotypes H :, . 17 . PA . .. - . .. ... .. · '. : . . . . . . . .. . .. . : 1 . . among the F, females: those with and those without the fourth-chromosome mutant phenotype; the latter type will have only 'mutant females in the fai Since this alternative gives Information on chromosomal diojunction, itlo . useful to note which is recovered in each case. Non-reciprocal interarm exchange. This is a difficult class to detect in some cases, for it involves determining whether a given marker is present once or twice. To do this, it is necessary to put the new fragment through the detachment process, and analyze a series of attached-X detachments derived from it. It is useful in testing these detachments to determine not only the linkage of the Y marker with the detachment, but also to test for fourth chromosome involvement. This is helpful in excluding the possibility of the recovery of an unmarked Y arm, by accounting for as many of the non-Y-marked detachments as practicable. In the process of testing a number of yellow.* - marked fragments, a useful correlation has appeared: fragments found to have yellow at both ends of the Y cause the fly to have a number of extra hairs in the wing, mainly in the second posterior cell. An additional number of : fragments are being tested by Dr. John Williamson to determine the reliability of this method of counting the number of yellow* duplications in the flies' .. - - chromosomes. Exchanges with X. It is possible that such exchanges occur, but none have as yet been detected. One procedure that might work would be to make a new array of detachments and test those not having yellow for the presence of the normal allele of lethai (1) J (201) :: ..:. :- . .. . . .... . Autosomal tip exchange. This procedure 18 similar to that for detachment, except that males carrying the chromosome to be tested are crossed to homozygous attached-XY fanaidh, woo homórygows for autosomal ond markers, and their sons are backcrossed to similar females. Mapping breaks in the Y. Y fragments are tested for presence of fertility loci by their ability to complement deficient Y'8. The simplest way to produce males of the desired genotype, 1.e., X/Y-fragment/Y-tester, 18 to cross attached-XY/Y-fragment males to Xxy females whose Y is one of the Brosseau deficient Y'B. Fertility tests are carried out in a similar manner to those described for detachments: mass matings, followed by individual matings where the mass mating has been successful, checking the phenotypes of the progeny i to verify that these are as expected from males carrying two Y chromosomes, marked as these particular ones are. It must be remembered that some of the tester stocks are "leaky" – ie. that w occasional functional sperm will be produced in a male carrying the uncomplemented tester chromosome; hence the necessity for individual matings. * 4. Tandem duplications and translocations. A useful method has been used by : Thomas and Roberts (1966) for detecting aberrations by looking for reduction in crossing over. They used widely-spaced markers, near either end of each : long chromosome and with one near the centromere in the case of the metacentrics. Aberrations were detected by examining those cases where crossover frequency among 25 offspring of a beterozygous female was significantly below the control value (95% confidence limits). ' . . :. :. More recently, Bender (1961) has utilized the method of pseudoallelic complementation to obtain tandem duplications of a specific locus, by Irradiating females heterozygous for the complementing alleles. .:.:. .......... 5. Disjunction following formation of the aberration: Recently, in this laboratory we have been asking the question, why is only half of a rearrangement recovered? Is it the fault of the method, that we look only for the results of that kind, or is it a consequence of how the newly-induced aberration behaves through the two meiotic divisions? We have been able to answer this questión in one situation by observing the origin of hyperploidy in the X-4 detachment classes. The question asked is what is the relationship between the two maternally-derived fourth chromosomes? Are they homologues or are they sisters? The answer also answers whether the two halves of the rearrangement separate at Anaphase I or at Anaphase II. For this type of experiment we have used different markers on the two maternal fourth chromosomes. Similarly, by using marked Y's and marked 4's, one can follow the disjunctional behavior of attached-X, when Y and 4 exchange, and of y when attached-X and 4 exchange, etc., and arrive at conclusions regarding the consequences, in terms of aneuploidy, of the induction of an aberration in a cell undergoing meiosis. . . '. .. 6. Partial recovery of translocations involving major autosomes. A direct outgrowth of the kinds of experiments outlined above 18 the development of a method for recovering one of the two elements resulting from a translocation between the major autosomes, chromosomes 2 and 3. Directed Anaphase I disjunction . ..... . ... ... -.... I ! - .,. . of the translocated. chromosomes should result in the inclusion, part of the time, of one of the exchange elements in the egg nucleus, with the other element going to one of the polar nuclei. The method for recovery of this aneuploid gamete 18 to cross the irradiated female to a male heterozygous for a translocation similar to the expected type. If the break-points were euchromatic, this might well be a hopeless task; if both break-points are : heterochromatic – i.e., if these are "whole arm" translocations – then an appropriate adjacent-disjunction product in the male should reasonably in complement the aneuploid egg nucleue. If each sex be homozygous with respect to markers, e.g., the female for recessives, the male for their normal alleles, and if there be one marker in each arm of chromosomes 2 and 3, the result of these processes will be a fly homozygous for the marker in one of the four arms, derived from the female, heterozygous for markers in two arms, and homozygous for the male-derived normal allele in the fourth arm. Backcrossing such exceptional flies to structural homozygotes al80 homozygous for the recessives carried by the treated female will verify the presence of a translocation, and by marker linkage analyze it as to arms involved. This method has recently been tested with succe88. It should be a simple matter now to devise similar methods of partial recovery that will allow screening for a number of other kinds of translocations, for example of X or of Y or of 4 with chromosomes 2 or 3, and to determine to a still finer degree than 18 now known the relationship of nuclear topology to the array of rearrangements it may be found possible to induce. - - - - - - - 9.. . . . .. . .. ....... 1*'s wide . ..::. . . :.. 7. Meiotic exchange as a method of genetic analysis. In determining the structure or sequence of heterochromatic elements it is not always feasible ::. to depend on spontaneous recombinations for the needed information. Recovery of single products of exchange permits taking the unknown heterochromatic element to pieces at a number of points, hence of determining what one can about its components and their sequence. This has already been mentioned in .::· relation to the analysis of some y fragments. More recently, we have used it in the analysis of some other kinds of derivative Y's and other infrequently recombining elements. In the same way that detachments can be used in analysis of chromosomes, it may in some cases be useful to go in the opposite direction: chromosomes can be converted, by irradiating them, into reversed metacentrics (attached X's, for example). If the question is whether a particular chromosomal segment 18 in one arm or the otber, this method gives an unequivocal answer: 1f it is in one arn, it will of necessity be included in the new attachment; 1f in the other it more to be excluded. :: :. . .: .:.: .:: .::. . ... ...... .. ...... ... ... ...,:. . o ! Mam u .. rma de la mam * .. . *...* '-:1 med f . Nowa » Literature Cited: Abrahamson, 8., I. H. Herskowitz, and H. J. Muller 1956. Identification of half-translocations produced by X-rays la dotaching attached-x chromosomes of Drosophila melanogaster. Genetics 41: 410-419. Bender, H. A. 1967. Radiation induced tandem duplications in Drosophila melanogaster. Genetics 55: 249-254. ; js. :::: .' . Brosseau, G. E., J1. 1959 Crossing-over between Y chromɔsomes in the male of Drosophila. Drosophila Inform. Serv. 32: 115. . :..... is, .::. Bucher, Nelly 1957 Experimentelle Untersuchungen über die Beziehungen zwischen Keimzellen und somatischen Zellen im Over von Drosophila melanogaster. Rev. Suisse zool 64: 91-188. iii.. . .'. . . Grell, R. F., and A. C. Chandley 1965 Evidence bearing on the coincidence of exchange and DNA replication in the oocyte of Drosophila melanogaster. Proc. Natl. Acad. Sci. U.S. 53: 1340-1346. . . . .. . .. .. Guyenot, E. and A. Nøville 1933 Les bases cytologiques de la théorie du "crossing-over". Les premieres phases de l'ovogénèse de Drosophila ... .. . . . Jacob, J. and J. L. Sirlin 1959. Cell fimction in the ovary of Drosophila. I. DNA classes in nurse cell nuclei as determined by autoradiography. : Chromosoma 10: 210-228. King, R. C., A. C. Rubinson and R. F. Smith 1956 Oogenesis in adult Drosophila melanogaster. Growth 20: 121-157. Koch, E. A., and R. C. King 1966. The origin and early differentiation of the egg chamber of Drosophila melanogaster. J. Morph. 119: 283-304. of the ovary of Drosophila melanogaster. daromosoma 1: 276-283. Parker, D. R. 1954 Radiation induced exchanges in Drosophila females. Proc. Natl. Acad. Sci. U.S. 40: 795-800. 1963 On the nature of sensitivity changes in oocytes of Drosophila melanogaster, 10 F. H. Sobels (Ed.) Repair from Genetic Radiation Damage, Pergamon, Oxford, pp. 11-19. :: 1965 Chromosome pairing and induced exchange in Drosophila. Mutation Res. 2: 523-529. 1967 Induced heterologous exchange at meiosis in Drosophila. I. Exchanges between Y and fourth chromosomes. Mutation Res. 4: 333-337. :: ... . .. : Parker, D. R. and A. E. Hammond 1958 The production of translocations in Drosophila oocytes. Genetics 43: 92-100. . ..... . ... Thomas, R. E., and P. A. Roberts. 1966 Comparative frequency of X-ray induced crossover-suppressing aberrations recovered from oocytes and sperm of Drosophila melanogaster. Cenetics 53: 855-862. Wllrgler, F. E., H. Ulrich and A. Schneider-Minder 1963 Variation of radiosensitivity during meiosis ad early cleavage in newly laid eggs of Drosophila melanogaster, in F. H. Sobels (Ed.) Repair from Genetic Radiation Damage, Pergamon, Oxford, pp. 101-106. Zalokar, M. 1959 sites of ribonucleic acid and protein syathesis in Drosophila.. Eapti. Cell Research 19: 184-186. VINU . ! END DATE FILMED 8 / 9 / 67 SWT KULIT .