Incidence of mosaic cell lines in vivo and malsegregation of chromosome 21 in lymphocytes in vitro of trisomy 21 patients: detection by fluorescence in situ hybridization on binucleated lymphocytes

In order to detect aneuploidy in interphase human lymphocytes, both in vivo and in vitro, fluorescence in situ hybridization (FISH) was carried out on binucleated cells cytokinesis-blocked by cytochalasin B at the first mitosis after phytohemagglutinin stimulation. A pericentric chromosome-21-specific DNA probe prepared from yeast artificial chromosome clone 881D2 by the polymerase chain reaction was employed. One thousand binucleated cells per individual were scored from cultures from twelve trisomy 21 patients aged 0.01-8.9 years (mean 4.3 years) and 20 normal children of similar age. Of trisomy 21 patients, increased frequencies of disomic cells in vivo (1.690+/-1.070%) and cells containing six signals with nondisjunction (0.822+/-0.554%) were found, compared with those of monosomic 21 cells in vivo (0.265+/-0.130%) and cells containing four signals with nondisjunction in normal children (0.369+/-0.250%; P=0.000 and P=0.000, respectively). These results show that malsegregation of chromosome 21 occurs more often in trisomic 21 cells than in disomic cells from normal children. The frequency of nondisjunction was significantly higher than the loss of chromosome 21 in both cultured trisomic (0.822+/-0.554% vs 0.043+/-0.049%, P=0.000) and disomic (0.369+/-0.250% vs 0.010+/-0.30%, P=0.000) cells. Comparisons of in vivo and in vitro data on aneuploidy indicate that a cell selection mechanism may exist in vivo. All these results show that FISH, with a chromosome-specific probe, on binucleated lymphocytes is a powerful tool for simultaneously detecting mosaic cell lines in vivo and malsegregation (loss and nondisjunction) of a corresponding chromosome in vitro in the same cell population.     

Increased nondisjunction of chromosome 21 with age in human peripheral lymphocytes

Fluorescence in situ hybridization (FISH) on binucleated cells with chromosome-specific DNA probes provides a convenient way to visualize reciprocal segregation patterns in daughter nuclei, and overcomes most problems related to the artefactual loss or gain of chromosomes that flaw chromosome preparations. In this study, FISH was employed to evaluate age- and sex-effects on spontaneous malsegregation, nondisjunction and loss of chromosome 21 in human lymphocytes after the first division in culture. A total of 68 healthy nonsmokers and nondrinkers of alcohol (37 males and 31 females) were grouped by age as Group I (0-10 years), Group II (20-30 years), Group III (40-50 years) and Group IV (60-70 years), with at least seven subjects per group and sex. FISH with a pericentric chromosome 21 specific DNA probe was carried out on binucleated lymphocytes, cytokinesis-blocked by cytochalasin B (6 microg/ml for 26 h) at 44 h after initiation of cultures.Linear regression analyses demonstrated a significant age-related increase in the frequency of micronuclei without chromosome 21 (MN-21)(r=0.73, p<0.001 in females; r=0.69, p<0.001 in males) in all binucleated cells, with a steeper slope in females (0.1758) than in males (0. 1241). Analysis using the 2x2 chi-square (chi(2)) test on the frequencies of MN-21 showed significant age-related differences in both males and females, except males in Group III and Group IV (p>0. 05). A significant sex-related difference was found only in subjects over 60 years (p<0.05), with females having more MN-21 (12.57 per thousand vs. 8.43 per thousand) than males.Loss of chromosome 21, occurring at mean levels of 0.38 per thousand in all binucleated cells and 0.24 per thousand in binucleated cells containing four FISH signals, was shown not to be age- or sex-related. A positive age-related increase in nondisjunction of chromosome 21 was shown in males (r=0.50, p<0.01), females (r=0.61, p<0.001) and all subjects (r=0.55, p<0.001) by linear regression analysis. An age effect was found only between children and adults (p<0.01 for females, p<0.05     

Sex chromosome loss and non-disjunction in women: Analysis of chromosomal segregation in binucleated lymphocytes

Chromosomal lagging and non-disjunction are the main mechanisms of chromosomal malsegregation at mitosis. To date, the relative importance of these two events in the genesis of spontaneous or induced aneuploidy has not been fully elucidated. A methodology based on in situ hybridization with centromeric probes in binucleated lymphocytes was previously developed to provide some insight into this matter. With this method, both chromosomal loss and non-disjunction can be simultaneously detected by following the distribution of specific chromosomes in the nuclei and micronuclei of binucleated cells. In this study, this approach was used for studying the role of chromosomal loss and non-disjunction in the age-related malsegregation of sex chromosomes in females. For this purpose, cultures of cytokinesis-blocked lymphocytes were established from 12 healthy women ranging in age from 25 to 56. The occurrence of malsegregation of X chromosomes in vitro was estimated in binucleated cells that contained four signals, which orginates from the division of normal disomic cells. In this cell population, the frequencies of X chromosome loss and non-disjunction ranged from 0% to 1.69% (mean 0.75%), and from 0.20% to 1.33% (mean 0.57%), respectively. This indicates that both events contribute to malsegregation of X chromosomes in vitro. Moreover, a small but not negligible fraction of binucleated cells with two or six copies of the X chromosome was noticed in all donors. These cells, which are thought to arise from parental monosomic and trisomic types, may indicate the malsegregation of X chromosomes in vivo. The frequency of X chromosome aneuploidy both in vivo and in vitro significantly correlated with the age of donors. Analysis of chromosomal distribution in unbalanced cells demonstrated that both X homologues were frequently involved. The frequency of such multiple events (0.17%) was far greater than that expected by mere chance, indicating a tendency to multiple malsegregation events in the cell population investigated. Finally, parallel analysis of the segregation of chromosomex X and 1 in five of the donors confirmed the greater (about tenfold) susceptibility of X chromosomes to malsegregate compared with autosomes.     

Genome instability is increased in lymphocytes of women with polycystic ovary syndrome and is correlated with insulin resistance

BACKGROUND: Polycystic ovary syndrome (PCOS) is associated with insulin resistance and reproductive and metabolic abnormalities. The potential genetic contributors to PCOS are unclear. We tested the hypothesis that genomic instability (chromosome malsegregation and DNA damage) is increased in PCOS. METHODS: Overweight age, weight and BMI-matched women with (n=14) and without (n=16) PCOS (age 34.2+/-6.0 years, weight 90.7+/-14.5 kg, BMI 34.0+/-5.6 kg/m(2), mean+/-S.D.) were assessed for chromosome malsegregation (assessed by X chromosome chromogenic in situ hybridisation) and micronucleus frequency (assessed by the cytokinesis block micronucleus index) in lymphocytes. RESULTS: Women with PCOS had significantly elevated genomic instability as demonstrated by a significantly higher number of binucleated lymphocytes containing micronuclei, total number of micronuclei, a higher proportion of aneuploid X chromosome signals (2:1 X and 3:1 X) and a lower proportion of normal X chromosome segregation signals (2:2 X) in binucleated lymphocytes than women without PCOS. Surrogate measures of insulin resistance positively correlated with the proportion of aneuploid cells (2:1; 3:1 X chromosome signals) and inversely with the proportion of normal cells (2:2 X chromosome signals). CONCLUSION: Women with PCOS display increased genomic instability (higher micronuclei and chromosome malsegregation) compared to women without PCOS and this increase may be related to the insulin resistance phenotype.     

Total aneuploidy and age-related sex chromosome aneuploidy in cultured lymphocytes of normal men and women

Summary In PHA-cultured lymphocytes, about 8% of metaphases from 32 women were aneuploid compared to 4% of metaphases from 35 men. A significant part of this aneuploidy was characterized by sex chromosome involvement: in women, the loss or gain of X chromosomes; in men, the gain of X chromosomes and the loss or gain of Y chromosomes. The incidence of this aneuploidy was positively age-related for both sexes. Premature division of the X-chromosome centromere was closely associated with X-chromosome aneuploidy in women and men, and appeared to be the mechanism of nondisjunction causing this aneuploidy. Premature centromere division (PCD) indicated a dysfunction of the X-chromosome centromere with aging, and this dysfunction was the basic cause of age-related aneuploidy. A similar mechanism of nondisjunction may operate for the Y chromosome of men, but could not be clearly demonstrated because of the low incidence of Y-chromosome aneuploidy.The balance of the aneuploidy was characterized by chromosome loss and the involvement of all chromosome groups. It was consistent with chromosome loss from metaphase cells damaged during preparation for cytogenetic examination.     

Absence of correlation between univalent formation and meiotic nondisjunction in aged female Chinese hamsters

The effects of maternal aging on the configuration of chiasmata, formation of univalents, and segregation of first meiotic (MI) chromosomes were investigated in young (5-8 mo) and old (16-19 mo) Chinese hamsters. Primary oocytes were collected only from mature follicles approximately 10 h before ovulation, and secondary oocytes were obtained from the oviducts 5 h after spontaneous ovulation. The average number of chiasmata per oocyte was significantly smaller in aged hamsters than in the young hamsters (P less than 0.001). Terminal chiasmata were found more frequently in the former group than in the latter one (P less than 0.001). These results coincided well with findings in the mouse. Since the 11 meiotic chromosomes could be divided into four morphologically distinguishable subgroups, it was possible to determine whether the same bivalent forming univalents at MI actually underwent nondisjunction in the following meiotic division. The incidence of both MI oocytes with a univalent pair and aneuploid MII oocytes due to first meiotic nondisjunction was significantly higher in the aged group than in the young group (P less than 0.01) and P less than 0.05, respectively). However, univalents occurred almost exclusively in the smallest metacentric chromosome group (96%), whereas nondisjunction took place nearly equally in each chromosomal subgroup. These results clearly showed that there was no correlation between the univalents seen at MI and nondisjunction during the first meiotic division.     

Chromosome errors at mitotic anaphase.

Errors in mitotic divisions were assayed using various satellite DNAs as probes, hybridized in situ, to show that they included nondisjunction, chromosome and chromatid lagging, chromatid malsegregation, and monopolar segregations. The total rates of error were 1.7, 1.1, and 0.6% for chromosomes X, 17, and 18, respectively. Lagging was the most common error for all chromosomes and chromatid malsegregation, a source of 3:1 segregations occurred at about the same frequency as nondisjunction. In some cells, lagging of both X chromatids occurred and there were several cells where both X chromosomes showed errors in segregation. The disjunction of chromosomes was shown to be independent of their segregation and is speculated to involve a different mechanism.     

低强度He-Ne激光照射人外周血淋巴细胞两组试验结果的分析

本文采用染色体畸变 (chromosomalaberration CA)试验和微核 (micronucleus)试验两种方法对低强度He Ne激光辐照育龄妇女外周血淋巴细胞。激光能量密度分别为 14.31J cm2 (辐照 5′)、2 8.6 2J cm2 (辐照 10′) ,5 7.2 4J cm2(辐照 2 0′) ,114.5 2J cm2 (辐照 40′)。照射血样后 ,染色体畸变试验检测其淋巴细胞染色体畸变率 ,激光照射及空白对照组 ,血样染色体畸变率分别为 4.2 9‰、3.96‰、3.81、3.5 9‰和 4.19‰ ,X2 检验无显著意义 (P >0 .0 5 )。阳性对照丝裂霉素MMC处理的血样淋巴细胞CA率平均为 14.41‰ ,明显高于激光照射和空白对照组 ,X2 检验有显著差异(P <0 .0 1)。微核试验检测结果 ,微核染色体分别为 1.0 2‰ ,1.17‰ ,1.18‰ ,1.31‰和 1.19‰对照 ,经统计分析激光照射各组与对照组微核率均在 2‰以下 (P >0 .0 5 ) ,属正常人体微核范围内。结果显示两组试验监测诱变均具有一致性。证明He Ne激光辐照人体细胞对染色体无致畸效应。且表明He Ne激光在治疗范围内应用安全、有效、不会对不体造成危害。     

Sex chromosome loss, micronuclei, sister chromatid exchange and aging: a study including 16 centenarians

In the present study we analysed the possible effect of age, sex and smoking on the mean values of micronucleus (MN) and sister chromatid exchange (SCE) frequencies on peripheral blood obtained from 38 subjects ranging in age from 16 to 63 years and 16 centenarians. The mean number of binucleated cells with micronuclei varied in function of age and sex (as demonstrated by the analysis of covariance (F=13.13; P<0.001), particularly evident was the increment observed in women with increasing age (interaction age/sex: F=5.53; P<0.05). Smoking habits had no effects on MN frequency (F=0.36; P>0.05). Sex (F=4.18; P<0.05) and smoking habits (F=14.64; P<0.001) influenced significantly SCE per cell frequencies, but age had no effects on them (F=2.45; P>0.05).The age-associated increase of sex chromosome loss was studied using fluorescence in situ hybridisation (FISH) on interphase nuclei.The loss of Y signals was observed in 10% of interphase cells from the centenarians males, that is six times more often than in the younger control men (1.6%). The frequency of X signal loss (1.7%) in young women was similar to that observed in male controls of the same age but the incidence of the X chromosome aneuploidy in centenarian females was appreciably higher (22%) than that found for the Y chromosome in males. These results were correlated with the data on MN formation and a positive correlation between the percentage of aneuploid cells (FISH) and MN values was observed (r=0.50; P<0.05).     

The mechanism of secondary nondisjunction in Drosophila melanogaster females

Bridges (1916) observed that X chromosome nondisjunction was much more frequent in XXY females than it was in genetically normal XX females. In addition, virtually all cases of X nondisjunction in XXY females were due to XX <--> Y segregational events in oocytes in which the two X chromosomes had failed to undergo crossing over. He referred to these XX <--> Y segregation events as "secondary nondisjunction." Cooper (1948) proposed that secondary nondisjunction results from the formation of an X-Y-X trivalent, such that the Y chromosome directs the segregation of two achiasmate X chromosomes to opposite poles on the first meiotic spindle. Using in situ hybridization to X and YL chromosomal satellite sequences, we demonstrate that XX <--> Y segregations are indeed presaged by physical associations of the X and Y chromosomal heterochromatin. The physical colocalization of the three sex chromosomes is observed in virtually all oocytes in early prophase and maintained at high frequency until midprophase in all genotypes examined. Although these XXY associations are usually dissolved by late prophase in oocytes that undergo X chromosomal crossing over, they are maintained throughout prophase in oocytes with nonexchange X chromosomes. The persistence of such XXY associations in the absence of exchange presumably facilitates the segregation of the two X chromosomes and the Y chromosome to opposite poles on the developing meiotic spindle. Moreover, the observation that XXY pairings are dissolved at the end of pachytene in oocytes that do undergo X chromosomal crossing over demonstrates that exchanges can alter heterochromatic (and thus presumably centromeric) associations during meiotic prophase.     

Activation status of the X chromosome in human micronucleated lymphocytes

The frequency of X chromosome aneuploidy in human female peripheral blood lymphocytes has been reported by several investigators to be significantly higher than expected based upon chance alone. Studies in our laboratory showed that 72% of the micronuclei in the peripheral blood of human females contained the X chromosome. Such a high frequency of X chromosome loss suggests that some unique mechanism may be responsible for this phenomenon. The present study was carried out to test the hypothesis that the lost or micronucleated chromsome is the inactive and not the active X. Blood samples were obtained from two unrelated females, 36 and 33 years of age, each with a different X; 9 reciprocal translocation. In each, the normal X chromosome is inactive and the translocated X is active. Isolated lymphocytes were cultured according to standard techniques and blocked with cytochalasin B. Using a modified micronucleus assay, we scored 10,000 binucleated cells from the 36 year old, while 9,500 binucleated cells were scored from the 33 year old. The slides were first labeled and the kinetochore status of each micronucleus was determined. This was followed by simultaneous hybridization with a 2.0 kilobase centromeric X chromosome-specific probe and a chromosome 9 specific whole chromosome painting probe. All micronucleated cells were relocated and scored for their probe status. A total of 217 micronuclei were scored from the two subjects, of which 96 (44.2%) contained the X chromosome. Of these 96 micronuclei, 80 (83.3%) contained the inactive X, based on the absence of chromosome 9 material in the micronucleus. These results support our hypothesis that the inactive X chromosome is preferentially included in the micronuclei, and suggest that the X chromosome hypoploidy observed at metaphase in aging women is a related phenomenon. Received: 5 May 1995 / Revised: 15 July 1995     

Preferential occurrence of chromosome 21 malsegregation in peripheral blood lymphocytes of Alzheimer disease patients

To further investigate our finding of high levels of spontaneous aneuploidy in somatic cells of Alzheimer's disease (AD) patients (Migliore et al. 1997), we studied the molecular cytogenetics of eight patients with sporadic AD and six healthy controls of similar age. Cytochalasin B-blocked binucleated peripheral blood lymphocytes from the AD patients and unaffected controls were used to measure micronucleus induction or other aneuploidy events, such as the presence of malsegregation in interphase nuclei (representing chromosome loss and gain). Dual-color fluorescence in situ hybridization (FISH) with differential labeled DNA probes was applied. We used a probe specific for the centromeres of chromosomes 13 and 21 combined with a single cosmid for the Down's syndrome region (21q22.2) to obtain information on spontaneous chromosome loss and gain frequencies for both chromosomes (13 and 21). FISH data showed that AD lymphocytes had higher frequencies of chromosome loss (evaluated as fluorescently labeled micronuclei) for both chromosomes, as well as higher frequencies of aneuploid interphase nuclei, again involving both chromosomes, compared to control lymphocytes. However, aneuploidy for chromosome 21 was more frequent than for chromosome 13 in AD patients. This preferential occurrence of chromosome 21 in malsegregation in somatic cells of AD patients raises the hypothesis that mosaicism for trisomy of chromosome 21 could underlie the dementia phenotype in AD patients, as well as in elderly Down's syndrome patients.     

Age-dependent inclusion of sex chromosomes in lymphocyte micronuclei of man.

Two-color centromeric FISH was used to study the inclusion of the X and Y chromosomes in micronuclei of cultured lymphocytes from 10 men representing two age groups (21-29 years and 51-55 years). In addition, pancentromeric FISH was separately performed to identify any human chromosomes in micronuclei. One hundred micronuclei per probe were examined from each donor. A higher mean frequency of Y-positive micronuclei was observed in the older men than in the younger men. In both age groups, the X chromosome was micronucleated clearly more often than expected by chance, and the Y chromosome was overrepresented in micronuclei among the older men but not among the younger men. In lymphocytes of four women, X-positive micronuclei were more frequent than they were in men, even after the fact that women have two X chromosomes was taken into account. Similar results were obtained in first-division lymphocytes identified by cytochalasin-B-induced cytokinesis block. In comparison with normal cells, these binucleate cells showed a higher frequency (per 1,000 nuclei) of X-positive micronuclei (in the older men) but a lower frequency of micronuclei harboring autosomes or acentric fragments. In conclusion, the results show that both the X chromosome and the Y chromosome are preferentially micronucleated in male lymphocytes, the Y chromosome only in older subjects. Although the X chromosome has a general tendency to be included in micronuclei, it is micronucleated much more often in women than in men, which is probably the main reason for the high micronucleus frequency in women that has been documented in many previous studies.     

Etoposide exposure during male mouse pachytene has complex effects on crossing-over and causes nondisjunction

In experiments involving different germ-cell stages, we had previously found meiotic prophase of the male mouse to be vulnerable to the induction of several types of genetic damage by the topoisomerase-II inhibitor etoposide. The present study of etoposide effects involved two end points of meiotic events known to occur in primary spermatocytes--chromosomal crossing-over and segregation. By following assortment of 13 microsatellite markers in two chromosomes (Ch 7 and Ch 15) it was shown that etoposide significantly affected crossing-over, but did not do so in a uniform fashion. Treatment generally changed the pattern for each chromosome, leading to local decreases in recombination, a distal shift in locations of crossing-over, and an overall decrease in double crossovers; at least some of these results might be interpreted as evidence for increased interference. Two methods were used to explore etoposide effects on chromosome segregation: a genetic experiment capable of detecting sex-chromosome nondisjunction in living progeny; and the use of FISH (fluorescence in situ hybridization) technology to score numbers of Chromosomes X, Y, and 8 in spermatozoa. Taken together these two approaches indicated that etoposide exposure of pachytene spermatocytes induces malsegregation, and that the findings of the genetic experiment probably yielded a marked underestimate of nondisjunction. As indicated by certain segregants, at least part of the etoposide effect could be due to disrupted pairing of achiasmatic homologs, followed by precocious sister-centromere separation. It has been shown for several organisms that absent or reduced levels of recombination, as well as suboptimally positioned recombination events, may be associated with abnormal segregation. Etoposide is the only chemical tested to date for which living progeny indicates an effect on both male meiotic crossing-over and chromosome segregation. Whether, however, etoposide-induced changes in recombination patterns are direct causes of the observed malsegregation requires additional investigation.     

Y染色体异常29例分析

本文从1992例遗传咨询病例中收集29例Y染色体异常的病例,其中Y染色体数 目异常(47,XYY)2例;Y染色体结构异常8例:Y/Y易位1例、Yp+3例、de l(Y)3例、嵌合 体dic(Y)1例;Y染色体长度变异19例。对Y染色体这几种异常类型的遗传效应进行分析。 Abstract:Twenty nine cases of Y chromosome abnormalities were found in 1992 patients asking genetic counseling.Different kinds of Y chromosome abnormalitics were detected by G and banding techniques.These were 47,XYY(2 cascs);46,X,del(Y)(3 cascs);46,X,Yp+(3 cases);46,X,t(Y;Y)(1 case);45,X/46,X,dic(Y)(1 case) and length changes of Y chromosome(19 cases).The genetic effects of Y chromosome abnormalities have been analyzed in this report.     

Achiasmate Segregation of a B Chromosome from the X Chromosome in Two Species of Psyllids (Psylloidea, Homoptera)

The segregation of a B chromosome from the X chromosome was studied in male meiosis in two psyllid species, Rhinocola aceris (L.) and Psylla foersteri (Flor.) (Psylloidea, Homoptera). The frequency of segregation was determined from cells at metaphase II. In R. aceris, the B chromosome was mitotically stable and segregated quite regularly from the X chromosome in four geographically distant populations, while it showed less regular, but preferential segregation in one population. This was attributed to the presence of B chromosome variants that differ in their ability to interact with the X chromosome in segregation. In P. foersteri, the B chromosome was mitotically unstable and segregated preferentially from the X chromosome in spermatocyte cysts, which displayed one B chromosome in every cell. Behaviour of the B chromosome and X chromosome univalents during meiotic prophase and at metaphase I in R. aceris, and during anaphase I in P. foersteri suggested that the regular segregation resulted from the incorporation of B chromosomes in achiasmate segregation mechanisms with the X chromosome in the place occupied by the Y chromosome in species with XY system. The regular segregation of a B chromosome from the X chromosome may obscure the distinction of a B chromosome and an achiasmate Y chromosome in some cases. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Genetic Analysis of Distributive Segregation in Drosophila Melanogaster. I. Isolation and Characterization of Aberrant X Segregation (Axs), a Mutation Defective in Chromosome Partner Choice

We describe the isolation and characterization of Aberrant X segregation (Axs), a dominant female-specific meiotic mutation. Although Axs has little or no effect on the frequency or distribution of exchange, or on the disjunction of exchange bivalents, nonexchange X chromosomes undergo nondisjunction at high frequencies in Axs/+ and Axs/Axs females. This increased X chromosome nondisjunction is shown to be a consequence of an Axs-induced defect in distributive segregation. In Axs-bearing females, fourth chromosome nondisjunction is observed only in the presence of nonexchange X chromosomes and is argued to be the result of improper X and fourth chromosome associations within the distributive system. In XX females bearing a compound fourth chromosome, the frequency of nonhomologous disjunction of the X chromosomes from the compound fourth chromosome is shown to account for at least 80% of the total X nondisjunction observed. In addition, Axs diminishes or ablates the capacity of nonexchange X chromosomes to form trivalents in females bearing either a Y chromosome or a small free duplication for the X. Axs also impairs compound X from Y segregation. The effect of Axs on these segregations parallels the defects observed for homologous nonexchange X chromosome disjunction in Axs females. In addition to its dramatic effects on the X chromosome, Axs exerts a similar effect on the segregation of a major autosome. We conclude that Axs defines a locus required for proper homolog disjunction within the distributive system.     

The TX; Y test for the detection of nondisjunction and chromosome breakage in Drosophila melanogaster. I. Analysis of spontaneous events and results of male exposure

The translocation X; Y test is a selective system in Drosophila melanogaster designed to detect and distinguish among sex chromosome nondisjunction, chromosome breakage, and X-Y interchange. In the test, only exceptional progeny survive. This enables the investigator to score thousands of progeny with relative ease. The distribution of spontaneous events occurring in individual TX; Y males are analyzed in this paper. Evidence is obtained suggesting that the clusters of two products arising from a single nondisjunction can significantly affect the distribution of recovered chromosome gain or chromosome loss events. Non-parametric statistical methods are therefore recommended for the analysis of TX; Y data. In addition, use of the TX; Y test following exposures of pre-adult males to X-rays, heat shock, cold shock, colchicine, dimethyl sulfoxide (DMSO), and trifluralin are presented. Significant increases in nondisjunction (both gain and loss) were obtained following exposures to heat shock, cold shock, DMSO and trifluralin. Significant increases in chromosome breakage and X-Y interchange were obtained after exposures to X-rays and heat shock. These results indicate that the TX; Y test is an efficient method for detecting aneuploidy. Further work is needed, however, to fully validate this system for the routine screening of aneuploidy-inducing agents.     

Genetic factors affecting normal growth of testes inDrosophila hydei

Summary A marked growth in the length of testes ofDrosophila hydei males occurred during pupal development. This growth continued over the first 8 days of adult life and in the young adults sperm were not produced until the testes increased approximately threefold in length to about 28 mm. The length of testes is correlated with genetic factors on the X and Y chromosomes. In males lacking a Y chromosome (X/O) or the short arm (Y^S) of the Y chromosome (X/Y^L) the testes were about half the length of testes of control males (X/Y) or double Y males (X/Y/Y). Males with deletions of the distal Y^L chromosome arm had testicular lengths equivalent to the controls. Males with short testes (X/O and X/Y^L) showed disruptions to spermatogenesis at meiosis and an absence of normal spermatid elongation. Reduction of active ribosomal RNA genes on the X chromosome in X/O caused an increased expression ofbobbed (bb) and a corresponding reduction in length of testes. Severelybobbed X/O males had very few cysts of spermatogonia and these cysts did not develop into primary spermatocytes.     

Meiosis in Male DROSOPHILA MELANOGASTER I. Isolation and Characterization of Meiotic Mutants Affecting Second Chromosome Disjunction

Two second chromosome, EMS-induced, meiotic mutants which cause an increase in second chromosome nondisjunction are described. The first mutant is recessive and causes an increase in second chromosome nondisjunction in both males and females. It causes no increase in nondisjunction of the sex chromosomes in either sex, nor of the third chromosome in females. No haplo-4-progeny were recovered from either sex. Thus, it appears that this mutant, which is localized to the second chromosome, affects only second chromosome disjunction and acts in both sexes.-The other mutant affects chromosome disjunction in males and has no effect in females. Nondisjunction occurs at the first meiotic division. Sex chromosome disjunction in the presence of this mutant is similar to that of sc(4)sc(8), with an excess of X and nullo-XY sperm relative to Y and XY sperm. In some lines, there is an excess of nullo-2 sperm relative to diplo-2 sperm, which appears to be regulated, in part, by the Y chromosome. A normal Y chromosome causes an increase in nullo-2 sperm, where B(s)Y does not. There is also a high correlation between second and sex chromosome nondisjunction. Nearly half of the second chromosome exceptions are also nondisjunctional for the sex chromosomes. Among the double exceptions, there is an excess of XY nullo-2 and nullo-XY diplo-2 gametes. Meiotic drive, chromosome loss and nonhomologous pairing are considered as possible explanations for the double exceptions.