Meiotic segregation, recombination, and gamete aneuploidy assessed in a t(1;10)(p22.1;q22.3) reciprocal translocation carrier by three- and four-probe multicolor FISH in sperm.

Meiotic segregation, recombination, and aneuploidy was assessed for sperm from a t(1;10)(p22.1;q22.3) reciprocal translocation carrier, by use of two multicolor FISH methods. The first method utilized three DNA probes (a telomeric and a centromeric probe on chromosome 1 plus a centromeric probe on chromosome 10) to analyze segregation patterns, in sperm, of the chromosomes involved in the translocation. The aggregate frequency of sperm products from alternate and adjacent I segregation was 90.5%, and the total frequency of normal and chromosomally balanced sperm was 48.1%. The frequencies of sperm products from adjacent II segregation and from 3:1 segregation were 4.9% and 3.9%, respectively. Reciprocal sperm products from adjacent I segregation deviated significantly from the expected 1:1 ratio (P < .0001). Our assay allowed us to evaluate recombination events in the interstitial segments at adjacent II segregation. The frequencies of sperm products resulting from interstitial recombination in chromosome 10 were significantly higher than those resulting from interstitial recombination in chromosome 1 (P < .006). No evidence of an interchromosomal effect on aneuploidy was found by use of a second FISH method that simultaneously utilized four chromosome-specific DNA probes to quantify the frequencies of aneuploid sperm for chromosomes X, Y, 18, and 21. However, a significant higher frequency of diploid sperm was detected in the translocation carrier than was detected in chromosomally normal and healthy controls. This study illustrates the advantages of multicolor FISH for assessment of the reproductive risk associated with translocation carriers and for investigation of the mechanisms of meiotic segregation of chromosomes.     

Sperm nuclei analysis of 1/29 Robertsonian translocation carrier bulls using fluorescence in situ hybridization

In 1964, Gustavsson and Rockborn first described the 1/29 Robertsonian translocation in cattle. Since then, several studies have demonstrated the negative effect of this particular chromosomal rearrangement on the fertility of carrier animals. During the last decade, meiotic segregation patterns have been studied on human males carrying balanced translocations using FISH on decondensed sperm nuclei. In this work, we have applied the 'Sperm-FISH' technique to determine the chromosomal content of spermatozoa from two bulls heterozygous for the 1/29 translocation and one normal bull (control). 5425 and 2702 sperm nuclei were scored, respectively, for the two heterozygous bulls, using whole chromosome painting probes of chromosomes 1 and 29. Very similar proportions of normal (or balanced) spermatozoa resulting from alternate segregation were observed (97.42% and 96.78%). For both heterozygous bulls, the proportions of nullisomic and disomic spermatozoa did not follow the theoretical 1:1 ratio. Indeed, proportions of nullisomic spermatozoa were higher than those of disomic sperma tozoa (1.40% vs 0.09% (bull 1) and 1.29% vs 0.15% (bull 2) for BTA1, and 0.65% vs 0.40% (bull 1) and 1.11% vs 0.63% (bull 2) for BTA29). The average frequencies of disomic and diploid spermatozoa in the normal bull were 0.11% and 0.05%, respectively.     

Analysis of segregation and aneuploidy in two reciprocal translocation carriers, t(3;9)(q26.2;q32) and t(3;9)(p25;q32), by triple-color fluorescence in situ hybridization

Meiotic segregation patterns of chromosomes 3 and 9 were analyzed in sperm of two translocation carriers (t(3;9)(q26.2;q32) and t(3;9)(p25;q32)) by triple-color fluorescent in situ hybridization (FISH) with a telomeric DNA probe in addition to two centromeric probes. The frequencies of each sperm product resulting from alternate or adjacent I, adjacent II and 3:1 segregation in a t(3;9)(q26.2;q32) translocation carrier were 88.35%, 5.44% and 5.94%, respectively. On the other hand, the frequencies of each sperm product in a t(3;9)(p25;q32) translocation carrier were 89.23%, 6.02% and 4.48%, respectively. Of all the sperm products, the frequency of normal or chromosomally balanced sperm in a t(3;9)(q26.2;q32) and a t(3;9)(p25;q32) were 52.49% and 47.25%, respectively. The frequencies of each sperm product resulting from various segregations were different between both carriers and significantly deviated from the expected frequencies. Additional dual-color and triple-color FISH were performed to analyze aneuploidy rates for chromosomes 12, 17, 18, X and Y in order to detect any interchromosomal effect; no evidence of an interchromosomal effect was found.     

Transmission of chromosomal abnormalities: participation of chromosomally unbalanced gametes in fertilization and early development of unbalanced embryos in the Chinese hamster

Using 14 Chinese hamster stocks with various reciprocal translocations, chromosomally unbalanced gametes were produced and used to investigate the participation of the unbalanced gametes in fertilization and the development of unbalanced embryos. The selection of chromosomally abnormal gametes during fertilization was investigated by the chromosomal analysis of meiotic cells in heterozygotes for the 14 reciprocal translocations and pronuclei of fertilized ova obtained from crossing these heterozygotes. Compared with the expected frequencies from meiotic metaphase II (MII) scoring, the frequencies of male pronuclei having commonly a deficiency of chromosome 1 (q14-->q42) or chromosome 3 (p23-->q31) in one-cell embryos decreased significantly. However, the frequencies of male pronuclei with other abnormalities were all consistent with those expected from MII scoring. In contrast, the frequencies of female pronuclei with any karyotype including the same ones, as those decreased in male pronuclei from the translocation heterozygotes were all consistent with those estimated from MII scoring. These results suggest that gametes with nullisomies as well as disomies for any chromosomal segments may mostly participate in fertilization, whereas some sperm nullisomic for the specific segments of chromosomes 1 and 3 may fail to fertilize. On the other hand, the zygotic selection of chromosomal imbalance was investigated by direct analyses of pre-implantation embryos from crosses between chromosomally normal females and male heterozygotes from the 14 stocks with various reciprocal translocations. The chromosomal and morphological analysis revealed that some embryos were arrested in development at the two-cell stage and their common abnormality was partial monosomy for chromosome 1 or 2. Embryos with partial monosomy including chromosomes 1, 3 and 4 showed arrested development at four-eight-cell stages. Among day 4 embryos, some chromosomally unbalanced embryos, mainly with a deficiency of other segments, such as chromosomes 1p, 2q, 5q and 8, had fewer blastomeres than karyotypically normal and balanced embryos. The homology between the mouse and the Chinese hamster chromosomes relating to the developmental abnormalities at early stages was partially confirmed.     

Segregation products of male mice doubly heterozygous for the RB(6.16) and RB(16.17) translocations: Influence of sperm karyotype on fertilizing competence under varying mating frequencies

The meiotic segregants of male mice heterozygous for Rb(6.16)24Lub and Rb(16.17)7Bnr were viewed, for the first time, at first cleavage metaphase. Chromosomes were analyzed after G-banding, C-banding, and karyotyping. To study sperm aging effects, chromosomes of 202 one-cell zygotes derived from males mating at intervals of approximately 3,14, and 21 days were examined. At least 89.6% of sperm-derived complements were products of 2:2 segregation; at most, a possible 6.4% were 3:1 segregants. The six expected types of 2:2 segregants, both balanced and unbalanced, were equifrequent in the total zygote population derived from sperm of all ages. When the data were analyzed according to mating frequency, the 3-day sperm population considered most likely to be fresh showed a deficiency of the segregant nullisomic for chromosome 6 and disomic for chromosome 17, when compared with the reciprocal segregant (P < 0.025) as well as to all other 2:2 segregants (P < 0.05). However, these sperm fertilized in greater numbers (P < 0.01) than their reciprocal segregant (disomic for 6 and nullisomic for 17) in the 14-day sperm population. While sperm with chromosomal abnormalities are capable of fertilization, the competence of segregants nullisomic for 6 and disomic for 17 apparently depends on the prior storage period in the male. Further, the results suggest that the effect of aneuploidy on sperm function is dependent on the specific chromosome(s) involved.     

Sperm analysis in a subfertile male with a Y;16 translocation, using four-color FISH.

Sperm analysis was performed in a male with oligoasthenoteratozoospermia (OAT) and a reciprocal t(Y;16) (q11. 21;q24), using four-color FISH. Intracytoplasmic sperm injection (ICSI) treatment in this patient had resulted in the birth of one chromosomally balanced and two chromosomally normal children. To assess the risk of having a chromosomally unbalanced conception after ICSI, morphologically normal spermatozoa were studied with a set of probes allowing detection of all segregation variants. There were 51% normal or balanced sperm cells. The fraction of sperm products resulting from alternate and adjacent I segregation was 87%, 12% were products of 3:1 disjunction, and the other 1% had other types of aneuploidy. If morphologically abnormal cells were also included in the FISH analysis, nearly 90% of all the spermatozoa were unbalanced. We conclude that although the majority of males with a Y/autosome translocation are infertile due to azoospermia, our patient produces sufficient morphologically and chromosomally normal spermatozoa to have chromosomally normal or balanced offspring after ICSI. Assuming that ICSI with an unbalanced spermatozoon from this patient would result in a nonviable embryo in many cases, the combination of in vitro and subsequent in vivo selection probably results in a risk of unbalanced offspring of much less than 50%. Hence, FISH studies on the sperm of translocation carriers are useful for estimating the risk of having unbalanced offspring after ICSI and in understanding the mechanisms underlying infertility in such carriers.     

Cytogenetic analysis of sperm from a male heterozygous for a 13;14 Robertsonian translocation

Summary Cytogenetic analysis of 121 sperm from a man heterozygous for a t(13;14) Robertsonian translocation was performed using the technique of in vitro penetration of hamster eggs. The frequency of sperm that were chromosomally unbalanced with respect to the translocation was 27%. The frequency of chromosomally normal (36%) and balanced (38%) complements was approximately equal, as theoretically expected. There was no evidence for an interchromosomal effect since the frequency of numerical chromosomal abnormalities (2.5%) and structural chromosomal abnormalities (10.7%) — both unrelated to the translocation — were within the normal range of control donors. The ratio of X-and Y-chromosome bearing sperm was equal, and there was no evidence for preferential segregation of the X chromosome with the translocation.     

Molecular analysis of the chromosomal equipment in spermatoza of a 46, XY, t(7;8) (q11.21;cen) carrier by using fluorescence in situ hybridization

The meiotic segregation of a balanced reciprocal translocation (7;8) (q11.21;cen) was analysed by interphase fluorescence in situ hybridization (FISH) on carrier spermatozoa. A dual interphase FISH technique was applied to 34527 decondensed sperm heads with chromosome-7- and chromosome-8-specific alpha-satellite probes. Analysis with such probes was possible according to the cytogenetic characteristics of these translocation breakpoints, which implied a centromeric breakpoint. The majority of the analysed nuclei (56.70%) showed normal (30.40%) or balanced (26.30%) chromosomal equipment resulting from alternate segregation during meiosis. A total of 14935 spermatozoa (43.26%) was unbalanced with a predominance of gametes resulting from adjacent-I (25.10%) or adjacent-II (11.10%) segregation ; such gametes could produce partial mono- or trisomies at term. The frequency of analysed cells resulting from a 3:1 segregation, which could induce complete mono- and trisomies at term, was 7.06%; 0.04% of scored cells were diploid. The same dual-FISH technique was carried out either with chromosome-15- and chromosome-18-specific probes or with gonosome-specific probes, in order to detect a possible interchromosomal effect. A significant increase of disomic18 spermatozoa was observed in the carrier. Such studies are not yet frequent. Multicolour-FISH seems a rapid and accurate tool for direct analyses of spermatogenetic segregation mechanisms in a carrier of balanced chromosomal abnormalities and provides interesting information for characterizing the possible risks for the offspring. Received: 14 November 1997 / Accepted: 19 December 1997     

FISH on sperm heads allows the analysis of chromosome segregation and interchromosomal effects in carriers of structural rearrangements: results in a translocation carrier, t(5;8)(q33;q13)

Using three-color fluorescence in situ hybridization (FISH) with specific DNA probes, we have determined the chromosome segregation pattern of the translocated chromosomes in a human male carrier of a reciprocal translocation, t(5;8)(q33;q13). At the same time, we have assessed the possible interchromosomal effect on pair 21 using dual-color FISH. The segregation results showed that a 45.12% of the spermatozoa analyzed resulted from alternate segregation, 38.31% resulted from adjacent I, 6.97% from adjacent II, and 6.56% from 3:1 segregation. Finally, 1.23% could be either diploid sperm or 4:0 segregation. In both types of adjacent segregations, an excess of products containing short translocated segments (adjacent I) and interstitial regions (adjacent II) were found. Products resulting from the presence of an interstitial chiasma in pair 5 (1.26%), were found much more frequently (P < 0.0001) than those resulting from an interstitial chiasma in pair 8 (0.13%) (evaluated after adjacent II segregation). In 3:1 segregation, the products containing one chromosome were observed more frequently than those containing three chromosomes (P < 0.0001). No evidence of an interchromosomal effect on chromosome 21 was detected, the percentage of disomy 21 being similar to that in the controls (0.23% vs. 0.37%). However, the percentage of diploid sperm (1.18%) was significantly higher (P < 0. 0001) than that in the controls (0.27%). FISH therefore appears to be a useful technique for assessing the percentage of abnormal sperm in translocation carriers. Their application in assisted reproduction centers could offer patients more accurate genetic counseling.     

Evaluation of segregation patterns of 21;21 Robertsonian translocation along with sex chromosomes and interchromosomal effects in sperm nuclei of carrier by FISH technique

Meiotic segregation patterns of carriers of Robertsonian translocations (RT) are important for assessing the risk of unbalanced forms. We investigated the ratio of sperm with t(21;21) to sperm with nullisomy for chromosome 21; the segregation of the t(21;21) along with sex chromosomes, and also interchromosomal effects on chromosome 10 by using three color fluorescence in situ hybridization (FISH) with telomere specific (Tel 21q) and centromere-specific alpha satellite probes for chromosomes X, Y, and 10. The percentage of cosegregation of t(21;21) with sex chromosomes (49.50%) and without sex chromosomes (46.98%) was not significant. There are no significant differences between the percentages of cosegregation of t(21;21) with chromosome X (23.36%) and with chromosome Y (26.16%). No evidence of an interchromosomal effect on chromosome 10 was detected, the percentage of chromosome 10 aneuploidy being similar to that in controls. In addition, the frequency of diploid sperm nuclei was not significantly higher in the carrier (0.32%) than in the controls (0.44%) (P > 0.05). The sex ratio was similar within the carrier and the controls and between the carrier and the control. Three color-FISH analysis, using different probe combinations, seems a rapid and accurate tool for direct analysis of meiotic segregation product.     

Failure of chromosomally abnormal sperm to participate in fertilization in the Chinese hamster.

The selection of chromosomally abnormal gametes was investigated in the Chinese hamster by direct chromosome analysis of meiotic cells and one-cell embryos obtained from crossing heterozygotes for two reciprocal translocations, T(1;3)7Idr and T(1;3)8Idr. Expected frequencies of male and female gametes with different chromosome constitutions were estimated by scoring of secondary meiotic metaphase (MII) cells in the translocation heterozygotes. The frequency of gametes with each karyotype that participated in fertilization was investigated in pronuclei from translocation heterozygotes in one-cell embryos obtained from crossing the heterozygotes with karyo-typically normal animals. Compared with the expected frequencies from MII scoring, the frequencies of male pronuclei having some karyotypes in one-cell embryos decreased significantly. The karyotypes of male pronuclei showing a decreased frequency were commonly characterized by a deficiency of the long-arm segment of chromosome 1 (q13----qter) or by a deficiency of almost the whole arms of chromosome 3. On the other hand, the frequencies of female pronuclei with the same karyotypes were all consistent with those estimated from MII scoring. These results suggest that sperm nullisomic for certain segments of some chromosomes may fail to participate in fertilization.     

Human sperm chromosome studies in a reciprocal translocation t(2;5)

Summary Sperm chromosome complements have been studied in a man heterozygous for a reciprocal translocation t(2;5)(p11;q15). Human sperm chromosomes were obtained after fertilization of zona-free hamster eggs. A total of 75 human sperm metaphases were analysed. Of the complements studied, 59 (78.6%) resulted from a 2:2 segregation and 16 (21.3%) from a 3:1 segregation, 4:0 segregation was not observed. Our results indicate that at least 36% of sperm complements were unbalanced with respect to the translocation. The frequency of other chromosome anomalies unrelated to the translocation was 16%.     

Meiotic products of two reciprocal translocations studied by multicolor fluorescence in situ hybridization

The sperm products of two male carriers of reciprocal translocations were studied by fluorescence in situ hybridization (FISH) using a combination of three probes for each translocation. One patient carried a t(2;18)(p21;q11.2), the other a t(8;9)(q24.2;q32). The probes selected included a centromeric marker for each chromosome involved in the translocation plus a third probe distal to the translocation breakpoint of one of the translocation chromosomes. This assay identifies alternate, adjacent 1, adjacent 2, and 3:1 types of meiotic products. It allows the identification of recombination events and also estimation of the frequency of diploidy. For the t(2;18), the frequency of normal and balanced sperm and of adjacent 1, adjacent 2, and 3:1 products was 43.6%, 29. 8%, 10.5%, and 12.8%, respectively. Similar segregation patterns had been reported for this donor by direct sperm karyotyping of sperm cells. For the t(8;9), the frequency of normal and balanced sperm and of adjacent 1, adjacent 2, and 3:1 products was 44.4%, 41%, 3.1%, and 9.4%, respectively. The frequency of complementary adjacent 1 products was statistically different in both the t(2;18) (P < 0. 0001) and the t(8;9) (P < 0.0001) carrier. When the number of adjacent 2 products with one translocation chromosome (regardless of normal or derivative) was compared to the number of adjacent 2 products with the second translocation chromosome (again, regardless of normal or derivative), no statistical difference was noted for either the t(2;18) (P = 0.32) or the t(8;9) (P = 0.69). Recombination events within the interstitial segment of chromosome 2 were statistically higher than those seen in chromosome 18 (P < 0. 0001), whereas in chromosomes 8 and 9, recombination in the interstitial segments was similar (P = 0.64). The rate of diploidy was similar in both the t(2;18) (0.5%) and the t(8;9) (0.6%). Thus, FISH provides chromosome information on the sperm products produced by translocation carriers, although it cannot provide an assessment of the full chromosome complement of the spermatozoon.     

Contribution of chromosomal imbalance to sperm selection and pre-implantation loss in translocation-heterozygous Chinese hamsters

Chinese hamster stocks with various structurally abnormal chromosomes have been produced by X irradiation. Among these stocks, 18 with various reciprocal translocations were used to investigate the participation of unbalanced gametes in fertilization and the development of unbalanced embryos. Among males as well as females heterozygous for the same translocation, there is no difference in the frequency of each disjunctional class. The participation of chromosomally unbalanced gametes in fertilization was investigated by chromosomal analysis of meiotic cells in heterozygotes for the 18 reciprocal translocations and pronuclei of fertilized ova obtained from crossing these heterozygotes. Compared with the expected frequencies from MII scoring, the frequencies of male pronuclei having a common deficiency of chromosome 1 (1q17-->1q42) or chromosome 3 (3p23-->3q31) decreased significantly in one-cell embryos. However, the frequencies of male pronuclei with other abnormalities were all consistent with those expected from MII scoring. In contrast, the frequencies of female pronuclei with any karyotype including the same abnormalities as those decreased in male pronuclei from the translocation heterozygotes were all consistent with those estimated from MII scoring. These results revealed clearly that most gametes with nullisomies as well as disomies for any chromosomal segments may participate in fertilization, whereas only male gametes nullisomic for certain segments of chromosomes 1 and 3 failed to participate in fertilization. The zygotic selection of chromosomal imbalance was also investigated by direct chromosomal and morphological analyses of preimplantation embryos from crosses between karyotypically normal females and male heterozygotes from the 18 stocks with various reciprocal translocations. These analyses revealed that some embryos were arrested in development at the two-cell stage. The karyotype of these two-cell embryos had a common deficiency in a segment of chromosome 1 or chromosome 2. Embryos with partial monosomy including chromosomes 1, 3, 4 and 5 showed arrested development at four- to eight-cell stages. Among day 4 embryos, some chromosomally unbalanced embryos, mainly with a deficiency of segments of chromosomes 1p, 1q, 2q, 5q, 7q and 8, had fewer blastomeres than karyotypically normal and balanced embryos. The homology between Chinese hamster and mouse chromosomes relating to abnormal embryogenesis at early stages has been partially confirmed from reported maps of chromosomes. The Chinese hamster is useful for further cytogenetic studies during the stages of meiosis and early embryogenesis.     

Meiotic segregation of human sperm chromosomes in translocation heterozygotes: report of a t(9;10)(q34;q11) and a review of the literature

Meiotic segregation products were studied in sperm from a man who was heterozygous for a reciprocal translocation, t(9;10)(q34;q11). A total of 171 sperm chromosome complements were studied by in vitro fertilization of hamster eggs. All possible 2:2 and 3:1 meiotic segregations were observed with the following frequencies: alternate, 41%; adjacent-1, 48%; adjacent-2, 5%; 3:1, 6%. Within alternate segregations, the number of normal sperm (35) was not significantly different from the number of sperm carrying a balanced form of the translocation (33), as expected. The proportion of sperm with an unbalanced form of the translocation was 60%. There was no evidence for an interchromosomal effect, since the frequencies of numerical (8%) and structural (15%) chromosomal abnormalities (both unrelated to the translocation) were within the normal range of control donors. The literature on a total of 10 translocation heterozygotes studied by sperm chromosome analysis was reviewed.     

Sperm chromosome analysis in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22)

Summary Human sperm chromosomes were studied in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22). The pronuclear chromosomes were analysed after in vitro penetration of golden hamster (Mesocricetus auratus) eggs. Ninety-four sperm chromosome spreads were examined, of which 34 contained the normal number 7 chromosome and 59 the inverted 6. This segregation was significantly different from the expected 1:1 ratio. The number of X- to Y-bearing sperm was 48 and 46 respectively. No sperm contained a recombinant chromosome caused by a crossover within the inversion. The frequency of chromosomal abnormalities in other chromosomes was 9.6%, which is not significantly different from the frequency observed in normal donors (8.9%) in our laboratory. These result suggest that the risk of chromosomally unbalanced sperm is not high for this paracentric inversion.     

CENP-B is not critical for meiotic chromosome segregation in male mice.

Centromere protein B (CENP-B) is a constitutive protein that binds to a highly conserved 17bp motif located at most mammalian centromeres. To determine whether disruption of this gene affects chromosome segregation in male germ cells, we evaluated the frequencies of disomic and diploid sperm in CENP-B heterozygous and homozygous null mice using the mouse epididymal sperm aneuploidy (m-ESA) assay, a multicolor FISH method with probes for chromosomes X, Y and 8. The specificity and sensitivity of the m-ESA assay was demonstrated using Robertsonian (2.8) translocation heterozygotes as positive controls for sperm aneuploidy. Our results show that the frequencies of disomic and diploid sperm did not differ significantly between CENP-B heterozygous and homozygous null mice (P> or = 0.5) or from 129/Swiss isogenic mice (P> or = 0.5) and B6C3F1 mice (P> or = 0.2). These findings indicate that CENP-B does not have an essential role during chromosome segregation in male meiosis.     

Detection of structural abnormalities in spermatozoa of a translocation carrier t(3;11)(q27.3;q24.3) by triple FISH

Structural chromosome abnormalities in spermatozoa represent an important category of paternally transmittable genetic damage. A couple was referred to our centre because of repetitive abortions and the man was found to be a carrier of a reciprocal translocation t(3;11)(q27.3;q24.3). A tailored fluorescence in situ hybridisation (FISH) approach was developed to study the meiotic segregation patterns in spermatozoa from this translocation carrier. A combination of three DNA probes was used, a centromeric probe for chromosome 11, a cosmid probe for chromosome 11q and a YAC probe for chromosome 3q. The frequency of spermatozoa carrying an abnormal chromosome constitution was compared with baseline frequencies in control semen specimens and it was found that a significantly higher percentage of spermatozoa carried an abnormal constitution for the chromosomes involved in the translocation. A normal or balanced chromosome constitution was found in 44.3% of the analysed spermatozoa, while the remainder exhibited an abnormal chromosome constitution reflecting different modes of segregation (15.9% adjacent I segregation, 6.5% adjacent II segregation, 28.9% 3 : 1 segregation, 0.8% 4 : 0 segregation, 3.6% aberrant segregation). The frequency of aneuploidy for chromosomes X, Y, 13 and 21 was assessed using specific probes but there was no evidence of interchromosomal effects or variations in the sex ratio in spermatozoa from the translocation carrier. In conclusion, structural aberrations can be reliably assessed in interphase spermatozoa using unique DNA probe cocktails, and this method provides insight into the genetic constitution of germ cells and enables evaluation of potential risks for the offspring. Received: 19 September 1997 / Accepted: 27 October 1997     

Chromosome segregation into the spermatozoa of two men heterozygous for different reciprocal translocations

Sperm chromosomes from two human males, each heterozygous for a different reciprocal translocation, were examined. Chromosomally normal sperm were found in equal numbers to those carrying the translocation in the balanced form, in both males. Alternate segregation was more common than adjacent segregation in both translocations. Male W. G. had a greater proportion of sperm containing chromosome abnormalities unrelated to the translocation than did J.S., the second made studied. J.S. however, had a greater frequency of chromosomally unbalanced sperm. The great majority of unbalanced sperm in both males was due to adjacent I segregation.     

Gamete segregation in female carriers of Robertsonian translocations

Eleven female carriers of either 45,XX,der(13;14) (q10;q10) or 45,XX, der(14;21)(q10;q10) underwent hormonal stimulation with the purpose of producing enough oocytes for in-vitro fertilization and preimplantation genetic diagnosis. Polar body biopsy was performed in those oocytes and FISH with painting probes was applied in their metaphase-like first polar body chromosomes. In this way, unbalanced, normal and balanced oocytes could be distinguished and segregation modes ascertained. der(14;21)(q10;q10) produced 42% unbalanced, 37% normal and 21% balanced oocytes (n = 86) while der(13;14)(q10;q10) generated 33% unbalanced, 51% normal and 16% balanced oocytes (n = 69). In both translocations the number of normal oocytes was significantly higher than the number of balanced oocytes. However, while the frequency of unbalanced events involving chromosome 13 and 14 was similar in der(13;14)(q10;q10), there were significantly more abnormalities involving chromosome 21 than 14 in the der(14;21) (q10;q10) cases. When comparing survival rates to term, trisomies from Robertsonian origin seem to survive more often than those originated by non-disjunction in non-translocation carriers. The meiotic segregation patterns found in female Robertsonian translocations are different from those described in male carriers, with higher rates of unbalanced gametes in females than in males.