Frequency Of Nondisjunction Research Articles

Nonrandom segregation of the mouse univalent X chromosome: evidence of spindle-mediated meiotic drive.

A fundamental principle of Mendelian inheritance is random segregation of alleles to progeny; however, examples of distorted transmission either of specific alleles or of whole chromosomes have been described in a variety of species. In humans and mice, a distortion in chromosome transmission is often associated with a chromosome abnormality. One such example is the fertile XO female mouse. A transmission distortion effect that results in an excess of XX over XO daughters among the progeny of XO females has been recognized for nearly four decades. Utilizing contemporary methodology that combines immunofluorescence, FISH, and three-dimensional confocal microscopy, we have readdressed the meiotic segregation behavior of the single X chromosome in oocytes from XO females produced on two different inbred backgrounds. Our studies demonstrate that segregation of the univalent X chromosome at the first meiotic division is nonrandom, with preferential retention of the X chromosome in the oocyte in approximately 60% of cells. We propose that this deviation from Mendelian expectations is facilitated by a spindle-mediated mechanism. This mechanism, which appears to be a general feature of the female meiotic process, has implications for the frequency of nondisjunction in our species.

The Drosophila wispy gene is required for RNA localization and other microtubule-based events of meiosis and early embryogenesis.

RNAs are localized by microtubule-based pathways to both the anterior and posterior poles of the developing Drosophila oocyte. We describe a new gene, wispy, required for localization of mRNAs to both poles of the egg. Embryos from wispy mothers arrest development after abnormal oocyte meiosis and failure of pronuclei to fuse. Our analysis of spindle and chromosome movements during meiosis reveals defects in spindle structures correlated with very high frequencies of chromosome nondisjunction and loss. Spindle defects include abnormally shaped spindles, spindle spurs, and ectopic spindles associated with lost chromosomes, as well as mispositioning of the meiosis II spindles. The polar body nuclei do not associate with their normal monastral arrays of microtubules, the sperm aster is reduced in size, and the centrosomes often dissociate from a mitotic spindle that forms in association with the male pronucleus. We show that wispy is required to recruit or maintain known centrosomal proteins with two types of microtubule organizing centers (MTOCs): (1) the central MTOC that forms between the meiosis II tandem spindles and (2) the centrosomes of the mitotic spindle. We propose that the wispy gene product functions directly in several microtubule-based events in meiosis and early embryogenesis and speculate about its possible mode of action.

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.

Unequal nondisjunction frequencies of trivalent chromosomes in male mice heterozygous for two Robertsonian translocations

Robertsonian (Rb) translocation heterozygosity may cause pairing problems during prophase and segregation irregularities at anaphase of meiosis I. These stages of meiosis I were studied in male mice doubly heterozygous for the two Rb chromosomes Rb(9.19)163H and Rb(16.17)8Lub. At pachytene both Rb chromosomes similarly showed pairing irregularities like unpaired segments. However, highly different nondisjunction frequencies of chromosomes forming the respective trivalents were found. The nondisjunction frequency of the Rb8Lub trivalent chromosomes was about 40%, whereas a very low frequency of nondisjunction was found in combination with the Rb163H trivalent. Since both trivalents were together in the same cell, differences in kinetochore function are assumed to be responsible for the diverse frequency of nondisjunction.

Analysis of chromosome loss and chromosome segregation in cytokinesis-blocked human lymphocytes: non-disjunction is the prevalent mistake in chromosome segregation produced by low dose exposure to ionizing radiation.

The aim of the present work was to examine in human lymphocytes, firstly, whether in vitro gamma-rays as compared with X-rays also induce chromatid malsegregation and at higher frequencies than chromosome loss and, secondly, whether the cytokinesis-blocked micronucleus assay combined with fluorescence in situ hybridization might be useful for the biomonitoring of individuals exposed to ionizing radiation. After irradiation, the relative frequencies of centromere-positive micronuclei decreased from 39.2% at 0.1 Gy to 21. 63% at higher doses. There was no statistically significant increase in MNCen+ frequencies at doses below 1 Gy (0.1, 0.25 and 0.5 Gy), but a statistically significant increase at 1 (P < 0.05) and 2 Gy (P < 0.001) was observed for all the donors. No significant differences in baseline and gamma-ray-induced non-disjunction frequencies for chromosomes 1 (P = 0.9) and 17 (P = 0.8) between individuals were detected. For radiation-induced non-disjunction, lower doses (0.1, 0. 25 and 0.5 Gy) of gamma-rays did not induce a statistically significant increase in non-disjunction frequencies whereas 1 Gy and above clearly induced a statistically significant increase in the total non-disjunction frequencies for all the donors (P < 0.05 at 1 Gy and P < 0.0001 at 2 Gy). The aneugenic effect of radiation is less clearly dose dependent at the lower doses, suggesting an apparent threshold below which no change could be demonstrated. At high radiation doses the major mechanism for gamma-ray-induced aneuploidy is related to chromosome loss through non-disjunction, as has been demonstrated using X-rays, and not through the formation of micronuclei.

Genetic variation in rates of nondisjunction: association of two naturally occurring polymorphisms in the chromokinesin nod with increased rates of nondisjunction in Drosophila melanogaster.

Genetic variation in nondisjunction frequency among X chromosomes from two Drosophila melanogaster natural populations is examined in a sensitized assay. A high level of genetic variation is observed (a range of 0.006-0.241). Two naturally occurring variants at the nod locus, a chromokinesin required for proper achiasmate chromosome segregation, are significantly associated with an increased frequency of nondisjunction. Both of these polymorphisms are found at intermediate frequency in widely distributed natural populations. To account for these observations, we propose a general model incorporating unique opportunities for meiotic drive during female meiosis. The oötid competition model can account for both high mean rates of female-specific nondisjunction in Drosophila and humans as well as the standing genetic variation in this critical fitness character in natural populations.

A possible centromeric 21/22 translocation as an alternative cause of nondisjunction in trisomy 21

Two cases with normal karyotype and an additional signal in chromosome 22 with the 13/21 alpha satellite DNA probe have been reported in the literature. In both, one of the parents had the same marker, so an inherited polymorphism was considered. Here we describe another family case which is the first related to aneuploidy.The patient is a 16 month old boy with Down syndrome, he is the second product of young non consanguineous parents, there is family history of a paternal cousin who was a malformed stillbirth. The G banding karyotype was 47, XY+21 and FISH with centromeric 13/21 probe showed 6 signals instead of 5. Cytogenetics analysis with G and C bands and dual FISH with 13/21 and 14/22 probes evidenced that the extra signal was in a chromosome 22, which was inherited from the father because he revealed 5 marks with the 13/21 probe and 4 with the 14/22.This rearrangement could be explained by an inherited polymorphism, cross-hybridization or a translocation between the centromeric region of chromosomes 21 and 22. In this case, the father could be a new mutation or the product of an adyacent 1 segregation inherited from an ancestor, without an abnormal phenotype but with the risk of nondisjunction during the pairing at meiosis. In order to prove this hypothesis for genetic counseling, it is necessary to establish the parental origin of the patient's extra chromosome 21, determine the frequency of nondisjunction in the father's semen by FISH analysis and complete cytogenetic studies in other paternal relatives.

Nondisjunction in human sperm: comparison of frequencies in acrocentric chromosomes

Acrocentric chromosomes may be particularly predisposed to nondisjunction because of the frequency of trisomy for these chromosomes in human spontaneous abortions and liveborns. Studies of aneuploidy in human sperm have provided data on only a few acrocentric chromosomes, with evidence that chromosome 21 has a significantly increased frequency of disomy. To determine whether other acrocentric chromosomes have a higher frequency of nondisjunction or if chromosome 21 is anomalous, disomy frequencies for chromosomes 13 and 22 were studied by fluorescence in situ hybridization (FISH) analysis of 51,043 sperm nuclei from five normal men for whom the frequency of disomy for chromosomes 15 and 21 was known. The mean frequency of disomy for chromosome 13 (0.19%) did not differ significantly from that for other autosomes; however, the frequency of disomy 22 (1.21%) was significantly elevated (P < 0.001, Mantel-Haenszel χ² test). The G-group chromosomes (Nos. 21 and 22) also showed a significantly increased frequency of disomy (0.75%) compared to acrocentric D-group chromosomes (viz., chromosomes 13 and 15; 0.15%) (P < 0.001, Mantel-Haenszel χ² test) and other autosomes (chromosomes 1, 2, 4, 9, 12, 13, 15, 16, 18, and 20; 0.13%) studied in the same men (P < 0.001, Mantel-Haenszel χ² test).

Chromosomal damage rate, aging, and diet.

Chromosomal damage as measured by frequency of translocations, acentric fragments, telomere shortening, nondisjunction, chromosome loss, aneuploidy, and micronucleus formation has been shown to increase progressively with age. Using the cytokinesis-block micronucleus technique, which provides an efficient measure of chromosomal breakage and loss, we have been able to show that aging can explain at least 25% of the variation in chromosomal damage rate in lymphocytes from both males and females. We have also performed cross-sectional and placebo-controlled intervention studies to determine the relationship between the micronucleus (MN) frequency in lymphocytes and diet, and blood status for vitamins C, E, B12, and folic acid. Our studies have shown that MN frequency in the 41- to 60-year age group is significantly lower in vegetarians when compared to nonvegetarians, but the reverse was true in males aged between 20 and 40 years. This was accounted for by a deficient/low B12 status in vegetarian males; there was no difference in the MN frequency of vegetarian and nonvegetarian subjects aged between 61 and 90 years. Results from this study also showed significant negative correlations of MN frequency with folic acid and vitamin B12 but not with vitamin C or vitamin E. In separate studies on healthy men aged 50-70, we have verified the significant negative correlation between vitamin B12 status in plasma and MN frequency (r = -0.315, p = 0.013) in subjects who were not vitamin B12 deficient and observed a significant positive correlation between MN frequency and homocysteine status (r = 0.414, p = 0.0086) in those men who were not vitamin B12 and/or folate deficient. These data suggest that MN frequency is minimized when plasma B12 is above 300 pmol/L and plasma homocysteine is below 7.5 mumol/L. Double-blind placebo-controlled intervention studies conducted over four months have shown that above RDI intake of vitamin E (30 x RDI) or folic acid (10 x RDI) did not produce a significant reduction in MN frequency in men aged 50-70 years. In the latter case plasma homocysteine was reduced from a mean value of 9.33 mumol/L to 8.51 mumol/L, a level that does not correspond with minimization of MN frequency. We have also tested the hypothesis that moderate wine drinking can protect against the DNA-damaging effect of hydrogen peroxide and found that there was a strong ex vivo inhibition (> 70%) of hydrogen peroxide-induced MN frequency by plasma samples from blood collected one hour after consumption of red or white wine, as compared to plasma samples collected immediately before wine consumption (p = 0.0008). However, only samples following red wine consumption produced a significant reduction in baseline MN frequency. The above results suggest that chromosome damage can be modulated, under selected circumstances, by diverse dietary factors.

ADrosophilaKinesin-like Protein, Klp38B, Functions during Meiosis, Mitosis, and Segmentation

We show thatklp38B,isolated as a mutation that dominantly prolongs blastoderm mitotic cycles in Drosophila, encodes a Drosophila kinesin-like protein. Further genetic analyses show that Klp38B not only functions during mitosis, but is also required for meiosis and abdominal segmentation. Sequence comparisons suggest that Klp38B encodes an amino-terminal microtubule motor domain, a central α-helical coiled-coil domain, and a C-terminal globular domain. Evidence that Klp38B is required during meiosis is that flies transheterozygous for mutations in bothklp38Bandnodhave a high frequency of 4th chromosome meiotic nondisjunction. Nod is a chromokinesin, a chromosome binding kinesin, that is believed to provide astral-exclusion forces during the metaphase stage of meiosis. Evidence that Klp38B is required during mitosis is that embryos from female germline clones ofklp38Bmutations have holes in the cuticle similar to a zygoticstring(dCDC25) phenotype. Also, anti-Klp38B antibody injection into precellularization blastoderm embryos causes developmental arrest and the formation of circular mitotic figures. We speculate, based on these phenotypes, that Klp38B is a chromokinesin that provides astral-exclusion forces on the chromosomes during meiosis and mitosis. Consistent with this hypothesis, we have identified an HMG-1 homologous region on Klp38B that could potentially bind AT-rich DNA sequences. Finally, we show thatklp38Bmutations have defects in abdominal segmentation, suggesting that Klp38B, like Xenopus chromokinesin Xklp1, might be involved in polar granule formation.

Alphoid variant-specific FISH probes can distinguish autosomal meiosis I from meiosis II non-disjunction in human sperm

Over the past few years, several groups have used fluorescence in situ hybridization (FISH) to study aneuploidy in human sperm. Several important observations have derived from these studies, including the demonstration of chromosome-specific variation in non-disjunction frequencies, and the possible association of aneuploidy with environmental agents and with increasing paternal age. However, an important technical limitation of these studies has been the inability to distinguish between autosomal non-disjunction occurring at meiosis I and meiosis II. In the present report, we describe a simple FISH-based approach designed to overcome this limitation. Using oligonucleotide probes capable of distinguishing subtle differences in the alpha satellite sequences of chromosome 17, we demonstrate that (in appropriate heterozygotes) it is possible to simultaneously identify disomic sperm and to determine the meiotic stage of origin of the additional chromosome. This novel approach has important implications for future FISH sperm studies, since the ability to distinguish between meiosis I and meiosis II non-disjunction will make it possible to determine whether putative etiological agents affect chromosome segregation at both, or only one, of the two meiotic stages.

Micronuclei, centromere-positive micronuclei and chromosome nondisjunction in cytokinesis blocked human lymphocytes following mitomycin C or vincristine treatment

The influence of sampling time on the frequencies of micronuclei, centromere-positive micronuclei and chromosome nondisjunction was investigated in binucleated lymphocytes following treatment with a known clastogen (mitomycin C) or an aneuploidy-inducing agent (vincristine sulfate). Cytochalasin B (6 μg/ml) was added 44 h after mitogen stimulation and cultures were harvested 12, 28, 36 and 48 h thereafter. Micronucleated cells and micronuclei were significantly induced by the two treatments at all sampling times. Furthermore, in situ hybridization with an `all centromeres' probe showed that vincristine-induced micronuclei were prevalently centromere-positive whereas in mitomycin C-treated cultures only a minor fraction of induced micronuclei contained the hybridization signals. Chromosome nondisjunction rates, as measured by in situ hybridization with chromosome 7- and 11-specific alphoid probes, significantly increased following vincristine treatment. Chromosome nondisjunction and total micronucleus frequencies were found to increase with time both in controls and in mutagen-treated cultures, whereas the percentage of centromere-positive micronuclei in the different treatments was not influenced by the sampling time. Our data suggest that even in the presence of 6 μg/ml cytochalasin B, the abnormal segregation of binucleated cells may contribute to the baseline level of micronuclei and influence the results obtained. The introduction of a short cytochalasin B treatment (between 12 and 28 h) in the cytokinesis-blocked micronucleus assay may avoid the cytochalasin B effect on micronucleus frequencies.

Indication for thresholds of chromosome non-disjunction versus chromosome lagging induced by spindle inhibitors in vitro in human lymphocytes.

Risk assessment from exposure to spindle inhibitors should take into account the possibility of threshold concentration-response curves for aneuploidy induction. We analysed concentration-dependent induction of chromosome non-disjunction by well known spindle poisons (colchicine, carbendazim, mebendazole and nocodazole) and a reference clastogen, methyl methanesulphonate (MMS) in vitro in human lymphocytes; and integrated these findings with earlier results of chromosome loss in micronuclei. Chromosome non-disjunction was estimated on cytokinesis-blocked lymphocytes after simultaneous fluorescent in situ hybridization labelling with two chromosome-specific centromeric probes (chromosomes 1 and 17). The frequencies of spontaneous non-disjunction showed important inter-individual variations and were surprisingly high (7.04-15.39%). Lower concentrations of aneugens did not induce a statistically significant increase of non-disjunction frequencies over the respective control levels, whereas higher concentrations clearly induced a concentration-dependent increase in the non-disjunction frequencies with the four aneugens tested. On the contrary, even at high concentrations, MMS induced a slight increase in the frequency of non-disjunction but without being statistically significant when compared with the control frequencies. We estimated the inflection points, the first statistically significant concentrations, the last non-statistically significant concentrations and the number of events from concentration-response curves of chromosome non-disjunction and chromosome loss. A threshold-type of concentration-response for non-disjunction is highly probable for colchicine and nocodazole. For carbendazim and mebendazole the inflection point fell above the first statistically significant concentrations. But since it is obvious from dose-response curves where the inflection point/threshold lies, it appears that the model might be picking up some irregularities (possibly due to experimental variability in the dose-response curve at concentrations greater than the threshold). For accurate estimation of the threshold, analysis of more concentrations or more cells might be needed. Our data strongly indicate that in cultured human lymphocytes chromosome non-disjunction is a major mechanism of aneuploidy induction by spindle inhibitors and since non-disjunction occurs at lower concentration than chromosome loss, the aneuploidy threshold should be estimated on the basis of non-disjunction rather than on micronuclei frequencies (chromosome loss).

Fluorescence in situ hybridisation with chromosome-specific centromeric probes: a sensitive method to detect aneuploidy

Cytochalasin B-blocked binucleate human lymphocytes from female donors have been used to measure micronucleus induction and other aneuploidy events after treatment with colchicine, vinblastine or carbendazim. For the aneuploidy events, centromeric probes for 6 selected chromosomes (1, 8, X, 11, 17, 18) were used to measure chromosome loss, addition and non-disjunction in the interphase nuclei of these binucleate cells. The chromosomes were probed in pairs using Cy-3 (red) and FITC (green) labels for the 2 different centromeric regions. For colchicine, the total non-disjunction frequencies for chromosomes 1 and 8 were similar to the total micronucleus frequencies, but were detected as significant at lower concentrations. For vinblastine (chromosomes 1 and 8) and carbendazim (all 6 chromosomes) the frequencies of non-disjunction far exceeded (7 and > 2-fold, respectively) the peak frequencies of micronucleus induction. Although most chromosomes exhibited similar sensitivity in all the aneuploidy events measured, there was an indication that chromosome X was more than susceptible to non-disjunction than the other chromosomes. We believe that measurement of non-disjunction in binucleate human lymphocytes using chromosome specific centromeric probes offers a sensitive method for detection of aneuploidy and is particularly appropriate for the establishment of thresholds.

A study of meiotic pairing, nondisjunction and germ cell death in laboratory mice carrying Robertsonian translocations

Frequencies of anaphase I nondisjunction, germ cell death and pairing abnormalities at pachytene were assessed in male mice singly heterozygous and homozygous for the Robertsonian (Rb) translocations: Rb (1.3)1Bnr, Rb(11.13)4Bnr and Rb(10.11)8Bnr. Rb homozygotes showed low frequencies of nondisjunction but substantial germ cell death. This germ cell death could not be attributed to problems at pachytene as Rb homozygotes showed no increase in pairing abnormalities over the (C3H/HeH x 101/H)F1 controls. Instead genic factors are involved. Rb heterozygotes showed substantial frequencies of nondisjunction and even greater germ cell death than found in the homozygotes. Pachytene pairing abnormalities were observed and it appears that these, together with genic factors, cause physiological perturbation of meiocytes, thereby promoting germ cell death, with nondisjunction of the trivalent as a sublethal response.

Mutant rec-1 eliminates the meiotic pattern of crossing over in Caenorhabditis elegans.

Meiotic crossovers are not randomly distributed along the chromosome. In Caenorhabditis elegans the central portions of the autosomes have relatively few crossovers compared to the flanking regions. We have measured the frequency of crossing over for several intervals across chromosome I in strains mutant for rec-1. The chromosome is approximately 50 map units in both wild-type and rec-1 homozygotes, however, the distribution of exchanges is very different in rec-1. Map distances expand across the gene cluster and contract near the right end of the chromosome, resulting in a genetic map more consistent with the physical map. Mutations in two other genes, him-6 and him-14, also disrupted the distribution of exchanges. Unlike rec-1, individuals homozygous for him-6 and him-14 had an overall reduction in the amount of crossing over accompanied by a high frequency of nondisjunction and reduced egg hatching. In rec-1; him-6 and rec-1; him-14 homozygotes the frequency of crossing over was characteristic of the Him mutant phenotype, whereas the distribution of the reduced number of exchanges was characteristic of the Rec-1 pattern. It appears that these gene products play a role in establishing the meiotic pattern of exchange events.

A mutation in CSE4, an essential gene encoding a novel chromatin-associated protein in yeast, causes chromosome nondisjunction and cell cycle arrest at mitosis.

The centromere, a differentiated region of the eukaryotic chromosome, mediates the segregation of sister chromatids at mitosis. In this study, a Saccharomyces cerevisiae chromosome mis-segregation mutant, cse4-1, has been isolated and shown to increase the nondisjunction frequency of a chromosome bearing a mutant centromere DNA sequence. In addition, at elevated temperatures the cse4-1 allele causes a mitosis-specific arrest with a predominance of large budded cells containing single G2 nuclei and short bipolar mitotic spindles. The wild-type gene, CSE4, is essential for cell division and encodes a protein containing a domain that is 64% identical to the highly conserved chromatin protein, histone H3. Biochemical experiments demonstrate that CSE4p has similar DNA-binding characteristics as those of histone H3 and might form a specialized nucleosome structure in vivo. Interestingly, the human centromere protein, CENP-A, also contains this H3-like domain. Data presented here indicate that CSE4p is required for proper kinetochore function in yeast and may represent an evolutionarily conserved protein necessary for assembly of the unique chromatin structure associated with the eukaryotic centromere.

Genetic analysis of Stellate elements of Drosophila melanogaster.

Repeated elements are remarkably important for male meiosis and spermiogenesis in Drosophila melanogaster. Pairing of the X and Y chromosomes is mediated by the ribosomal RNA genes of the Y chromosome and X chromosome heterochromatin, spermiogenesis depends on the fertility factors of the Y chromosome. Intriguingly, a peculiar genetic system of interaction between the Y-linked crystal locus and the X-linked Stellate elements seem to be also involved in male meiosis and spermiogenesis. Deletion of the crystal element of the Y, via an interaction with the Stellate elements of the X, causes meiotic abnormalities, gamete-genotype dependent failure of sperm development (meiotic drive), and deposition of protein crystals in spermatocytes. The current hypothesis is that the meiotic abnormalities observed in cry- males is due to an induced overexpression of the normally repressed Ste elements. An implication of this hypothesis is that the strength of the abnormalities would depend on the amount of the Ste copies. To test this point we have genetically and cytologically examined the relationship of Ste copy number and organization to meiotic behavior in cry- males. We found that heterochromatic as well as euchromatic Ste repeats are functional and that the abnormality in chromosome condensation and the frequency of nondisjunction are related to Ste copy number. Moreover, we found that meiosis is disrupted after synapsis and that cry-induced meiotic drive is probably not mediated by Ste.

Dual color fluorescence in situ hybridization to investigate aneuploidy in sperm from 33 normal males and a man with a t(2;4;8)(q23;q27;p21)

To establish the relative frequency of aneuploidy in sperm from normal and abnormal subjects using dual color fluorescence in situ hybridization and probes for six different chromosomes. Semen from 33 normal males and a patient with a translocation was studied using dual color fluorescence in situ hybridization with probes for chromosomes 4, 7, 8, 12, 18, X and Y. The frequency of aneuploidy for each chromosome is compared with one another and with the patient who had a t(2;4;8)(q23;q27;p21). Specimens were obtained from patients at the Mayo Clinic, Rochester, Minnesota. The percentage of sperm with disomy or nullisomy in normal subjects ranged from 0.2% to 0.6% for each of the chromosomes studied. No statistically significant differences were observed between these chromosomes. The frequency of aneuploidy in sperm from a patient with a t(2;4;8) was 3.3% and 4.8% for chromosomes 4 and 8, respectively. Fluorescence in situ hybridization was useful to establish the normal range of nullisomic and disomic sperm for six different chromosomes and to study a patient with a clinically significant chromosome abnormality. In normal males, no difference in the frequency of meiotic nondisjunction was observed among the chromosomes studied.

Mechanism of the Induction of Chromosomal Errors, Interchromosomal Effects in Chinese Hamsters Heterozygous for Inversions

ABSTRACT Using Chinese hamsters heterozygous for inversions of chromosomes 1 or 4 [INV(1)37Idr and INV(4)Idr], as well as karyotypically normal animals, interchromosomal effects on meiotic disjunctions were investigated by chromosomal analysis of the meiotic cells and one‐cell conceptuses. The mean frequency of nondisjunction at the first meiosis in five normal +/+ males was calculated at 1.28%, by doubling the frequency (0.64%) of hyperhaploid second meiotic (MII) cells, and there was no significant difference in the frequency among individuals. Among males heterozygous for INV(1)37Idr or INV(4)25Idr inversion, the frequencies of hyperhaploid cells with an extra inversion‐unrelated chromosome were 0.52% and 0.43%, respectively, which were not significantly different from the frequency of hyperploid MII cells in +/+ males (0.52%). In one‐cell conceptuses obtained from crosses between karyotypically normal females and males heterozygous for INV(1)37Idr or INV(4)25Idr, 1.18% and 1.22% of conceptuses had an extra inversion‐unrelated chromosome, respectively. The frequency of nondisjunction during meiotic divison in males heterozygous for these inversions was not significantly different from that in controls. The results therefore suggest that the presence of inversions in meiotic cells exerts no influence on disjunctions of normal bivalents and MII chromosomes unrelated to the inversions.