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.     

Sperm chromosome complements from two human reciprocal translocation heterozygotes

Summary Using the hamster oocyte/human sperm fusion technique, we studied sperm chromosome complements in two male reciprocal translocation heterozygotes, 46,XY,t(11;17)(p11.2;q12.3) and 46,XY,t(1;11) (p36.3;q13.1). For the t(11;17) carrier, 202 sperm chromosome complements were obtained, but 18 karyotypes were not included in the segregation data because of multiple breaks and rearrangements. The alternate and adjacent I types, adjacent II, and 31 segregations accounted for 38.6%, 32.1%, 26.6%, and 2.7% of the sperm analyzed from the t(11;17) carrier. A total of 575 sperm chromosome complements was obtained using sperm from the t(1;11) heterozygote, and 27 karyotypes were excluded from the segregation data because of multiple breaks and rearrangements. For the t(1;11) carrier, the alternate and adjacent I types, adjacent II, and 31 segregations were responsible for 31.4%, 42.9%, 15.9%, and 8.0% of the analyzed sperm chromosome complements. Chromosomal abnormalities unrelated to the translocation, particularly the conservative estimate of aneuploidy frequency, were within the range observed in normal men. Hence, there was no evidence for an interchromosomal effect causing meiotic nondisjunction, despite the large sample sizes studied.     

Cytogenetic and molecular identification of three Triticum aestivum-Leymus racemosus translocation addition lines

Chromosome 2C from Aegilops cylindrica has the ability to induce chromosome breakage in common wheat （Tritivum aestivum）. In the BC1F3 generation of the T. aestivum cv. Chinese Spring and a hybrid between T. aestivum-Leymus racemosus Lr.7 addition line and T. aestivum-Ae, cylindrica 2C addition line, three disomic translocation addition lines （2n = 44） were selected by mitotic chromosome C-banding and genomic in situ hybridization. We further characterized these T. aestivum-L, racemosus translocation addition lines, NAU636, NAU637 and NAU638, by chromosome C-banding, in situ hybridization using the A- and D-genome-specific bacterial artificial chromosome （BAC） clones 676D4 and 9M13; plasmids pAsl and pSc119.2, and 45S rDNA; as well as genomic DNA of L. racemosus as probes, in combination with double ditelosomic test cross and SSR marker analysis. The translocation chromosomes were designated as T3AS-Lr7S, T6BS-Lr7S, and T5DS-Lr7L. The translocation line T3AS-Lr7S was highly resistant to Fusarium head blight and will be useful germplasm for resistance breeding.     

Quantitative analysis of diploid translocation heterozygotes: test of models and equations

Summary Equations have been derived for two different models of chromosome pairing and chiasmata distribution. The first model represents the normal condition and assumes complete synapsis of homologous bivalents and the arms of interchange quadrivalents. This is followed by a nonrandom distribution of chiasmata among bivalents and multivalents such that each bivalent or bivalent-equivalent always has at least one chiasma. Univalents occur only as part of a III, I configuration at diakinesis or metaphase I. The second model assumes that a hologenomic mutation is present in which all chromosomes of a genome are equally affected. Two different assumptions can be made for such a mutation, and both give the same results: (1) homologous or homoeologous chromosome arms may be randomly paired or unpaired, but synapsis always leads to a crossover; (2) homologous or homoeologous arms always pair, but chiasmata are randomly distributed among the arms. The meiotic configurations at diakinesis or metaphase I are the same for both assumptions. Meiotic configurations of normal diploid interchange heterozygotes show good agreement with numbers predicted by the equations for nonrandom chiasmata distribution among configurations. Inter-specific hybrids with supernumerary chromosomes produced meiotic configurations frequencies in agreement with predictions of equations for random chiasmata distribution, but a hybrid without supernumeraries fitted the nonrandom expectations.     

Cytogenetic studies in motile sperm from normal men

Summary Most studies on human sperm chromosomes from normal men involve the heterologous fertilization of zona free hamster eggs by unselected human sperm. In this work, we have performed cytogenetic studies of highly motile sperm, selected by a swim-up method. A total of 505 motile human sperm complements from three normal donors was analysed. The total frequency of sperm with chromosomal abnormalities (10.9%; 6.9% structural aberrations and 4.0% aneuploidy) and the sex ratio (50.4% X49.6% Y) were similar to those obtained from whole semen samples. Our results indicate that the selection of motile sperm does not imply chromosomal selection.     

The evolution of recombination in permanent translocation heterozygotes

The evolution of a selectively neutral locus that controls the degree to which alleles at a single selected locus are linked with a particular set of chromosomes in a permanent translocation heterozygote is studied. With complete selfing and fitness overdominance a new allele at the modifying locus will increase in frequency if it increases the linkage of all alleles at the selected locus to a particular set of chromosomes. With random mating a new allele at the modifying locus will increase when rare if it increases the linkage of alleles at the selected locus to a particular set of chromosomes. In addition, a parameter analogous to the coefficient of linkage disequilibrium in usual two-locus models with random mating must be nonzero if a new allele at the modifying locus is to increase in frequency at a geometric rate when rare. With mixed selfing and random mating a new allele at the modifying locus will apparently increase when rare only if it increases the linkage of alleles at the selected locus to a particular set of chromosomes.     

Cytogenetic studies in human sperm

Summary Sperm chromosome studies were performed in seven males. One of them had a history of exposure to lysergic acid (LSD) although he was free of the drug for 1 year before the study began. Sixteen ejaculates provided a total of 555 fully analyzable sperm cells. The overall frequency of hyperhaploid sperm cells was 2% and that of structural abnormality 3.6%. The most common structural abnormality was chromosome breaks followed by small chromosome fragments of unknown origin. Three chromosome breakpoints, 10q25, 2q21, and 9q21, were involved twice in different chromosome or chromatid type aberrations. Two of these, 10q25 and 2q21, correspond to chromosomal locations known as common fragile sites.     

Negative crossover interference in maize translocation heterozygotes.

Negative interference describes a situation where two genetic regions have more double crossovers than would be expected considering the crossover rate of each region. We detected negative crossover interference while attempting to genetically map translocation breakpoints in maize. In an attempt to find precedent examples we determined there was negative interference among previously published translocation breakpoint mapping data in maize. It appears that negative interference was greater when the combined map length of the adjacent regions was smaller. Even positive interference appears to have been reduced when the combined lengths of adjacent regions were below 40 cM. Both phenomena can be explained by a reduction in crossovers near the breakpoints or, more specifically, by a failure of regions near breakpoints to become competent for crossovers. A mathematical explanation is provided.     

Cytogenetic analysis of human spermatozoa using intracytoplasmic sperm injection into mouse oocytes

The chromosome complement of human spermatozoa has been analyzed after their intracytoplasmic injection into unfertilized mouse oocytes. A total of 427 metaphase plates have been obtained, including 176 metaphase plates from spermatozoa with normal head morphology (108 and 68 spermatozoa from patients with normal (the control group) and abnormal spermogram parameters, respectively), and 251 metaphase plates from spermatozoa with abnormal heads (76, 91, 67, and 17 spermatozoa with large, amorphous, elongated, and round heads, respectively). The frequency of chromosome abnormalities in the control group is 26.1%, with hyperploidy, hypoploidy, and structural aberrations accounting for 7.4, 12.3, and 6.4% of the abnormalities, respectively. In none of the groups did the ratio between the numbers of X- and Y-bearing spermatozoa significantly differ from 1 : 1. The diploidy frequency was significantly higher in spermatozoa with large and amorphous heads compared to the control group (2.36, 3.29, and 0%, respectively). None of the groups of spermatozoa differed from the control group with respect to the frequency of structural aberrations. The type of the abnormal head morphology has been found to be correlated with the sperm chromosome complement.Translated from Genetika, Vol. 41, No. 3, 2005, pp. 396–404.Original Russian Text Copyright © 2005 by Fedorova, Kuznetsova, Baranov, Rybouchkin, Van der Elst, Dhont.     

Cytogenetic analysis of human spermatozoa using intracytoplasmic sperm injection into mouse oocytes

The chromosome complement of human spermatozoa has been analyzed after their intracytoplasmic injection into unfertilized mouse oocytes. A total of 427 metaphase plates have been obtained, including 176 metaphase plates from spermatozoa with normal head morphology (108 and 68 spermatozoa from patients with normal (the control group) and abnormal spermogram parameters, respectively), and 251 metaphase plates from spermatozoa with abnormal heads (76, 91, 67, and 17 spermatozoa with large, amorphous, elongated, and round heads, respectively). The frequency of chromosome abnormalities in the control group is 26.1%, with hyperploidy, hypoploidy, and structural aberrations accounting for 7.4, 12.3, and 6.4% of the abnormalities, respectively. In none of the groups did the ratio between the numbers of X- and Y-bearing spermatozoa significantly differ from 1 : 1. The diploidy frequency was significantly higher in spermatozoa with large and amorphous heads compared to the control group (2.36, 3.29, and 0%, respectively). None of the groups of spermatozoa differed from the control group with respect to the frequency of structural aberrations. The type of the abnormal head morphology has been found to be correlated with the sperm chromosome complement.     

Cytogenetic analysis of three genetic sexing strains of Ceratitits capitata

Summary Polytene chromosomes of three genetic sexing strains of Ceratitis capitata were analyzed. The genetic sexing mechanism is based on a pupal color dimorphism (white-brown) and is the result of a reciprocal translocation between the Y chromosome and the autosome bearing the w locus (white pupal case). The analyzed polytene chromosomes were derived from two different pupal tissues, the orbital bristle and fat body cells. The Y chromosome is visible in both tissues, while the autosomes present a different banding pattern. Based on these features, the autosome breakpoints in the three Y; autosome translocations were mapped, and the homology of the translocated autosome in both tissues was established. In addition, the location of the break-points was compared to the stability of these three strains.     

Meiosis in translocation heterozygotes in the mosquito Culex pipiens

Adult Culex pipiens males irradiated with both X-rays and neutrons were crossed to untreated females and F₁-egg rafts were checked for dominant lethality. F₁-progenies were outcrossed with normal individuals in order to obtain lines with inherited semisterility. From a total of 120 lines that showed a certain amount of sterility 12 lines were studied cytologically. 10 lines showed reciprocal chromosome exchanges.—At late pachytene and diplotene cross configurations with large asynaptic regions at the center of the cross are obligatory. Bivalents, chains of three, chains of four, and ring configurations are present at metaphase and anaphase I. The different frequencies of the occurrence of such multiples are dependent on the chromosomes involved in the exchange, the length of the pairing segments and the chiasma frequencies in these segments. Chiasma frequency in the interstitial segments is reduced by means of chiasma interference over the centromere and by asynapsis near the breakage points. — Alternate, adjacent-1- and adjacent-2-distributions are present to a different extent. Alternate distribution is most, adjacent-2-distribution least frequent. — The role of translocations and the probability of their becoming effective in pest eradication programs is discussed.     

Isolation of telotertiary compensating trisomics from telocentric translocation trisomics and telo-substituted translocation heterozygotes of rye (Secale cereale L.)

Telotertiary compensating trisomics (CTs) of rye (Secale cereale L.), in which the absence of one normal chromosome is compensated by the presence of a telocentric and a translocation chromosome, were isolated in progenies of telocentric translocation trisomics, and telo-substituted translocation heterozygotes, respectively. These two sources were obtained from crosses between five interchanges of the Wageningen translocation tester set, and telocentric normal trisomics (for IRS, IRL and 5RS), or telocentric substitutions (for IR and 3R), respectively. In test crosses with normal male plants, CTs were identified using either critical meiotic configurations, the segregation of karyotypes in selfed trisomic progenies, or the segregation of a marker located on the compensated chromosome. CT yields ranged from 0.0–6.3%. These frequencies were concluded to be determined mainly by the frequency of the exchanged segment of the translocation chromosome involved in the CT complex being associated at first meiotic metaphase (MI) in the source plants. The lower association frequencies result in the higher CT yields. The correlation between high association frequency of this segment and low CT yield suggests that infrequent adjacent orientation of one critical segment is also responsible for the origin of CTs. This agrees with cytogenetic theory.     

A single locus model of selection in permanent translocation heterozygotes

A model for evolution at a single locus in permanent translocation heterozygotes is described. It is also applicable to other permanent structural heterozygotes that possess the mating systems discussed. Recombination occurs between the locus and the chromosomes, which are of two types. The mating system includes selfing and random mating. When recombination is rare, selection will result in almost complete fixation on the single most fit genotype present in a population, regardless of the frequency of selfing. This provides a possible explanation for the ecological success of permanent translocation heterozygotes in some groups of organisms, like Oenothera. It is not necessary to postulate that their success is the result of hybrid vigor. Furthermore, a complete lack of recombination is not necessary for explaining the observed association of alleles with particular segmental arrangements. A small amount of recombination is consistent with the observation that different segmental arrangements often carry different alleles.     

Allozyme genetics in permanent translocation heterozygotes of the Oenothera biennis complex

Allozyme inheritance and transmission genetics of 11 enzyme systems were determined in the permanent translocation heterozygotes Oenothera biennis, Oe. strigosa, and Oe. parviflora. Electrophoretic variation was examined first among 164 strains of structural heterozygotes. Allelic configurations were then judged from inheritance patterns in reciprocal F1 hybrids between each of 22 ring-forming strains and tester strains of the related bivalent-formers, Oe. hookeri and Oe. grandiflora. Allozymes are inherited as codominant markers, and, as dictated by the genetic system, within a strain individual allelic variants are generally transmitted through only one germ line. Of the 20 loci resolved, only eight are polymorphic in any species, and, within species, generally only two alleles are present at each polymorphic locus. Despite the relatively meager allelic array, each of the 22 strains whose chromosome complexes were characterized is genotypically unique. Generally, within taxa, alpha (egg) and beta (sperm) complexes differ in allele frequency at several polymorphic loci. Such variability is correlated with differences in the phylogenetic origins of complexes and not with differences in segmental arrangement within a group of related complexes.