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Biomedical subjects

K Fredga

Publications and source records attributed to K Fredga.

At least 37 records · Page 2Linked to original sources
PubMed1989

Absence of synapsis during pachynema of the normal sized sex chromosomes of Microtus arvalis.

The pachytene behavior of the chromosomes of males of Microtus arvalis (Pall.) (Rodentia, Arvicolidae) was examined by electron microscopy in microspread preparations of spermatocytes. There was no synapsis between the axes of these two chromosomes during this period. Since synapsis is universally considered a prerequisite for crossing over and chiasmata formation, disjunction of the sex chromosomes in this species prerequisite for crossing over and chiasmata formation, disjunction of the sex chromosomes in this species must be presumed to be achiasmatic. Unlike previously examined species with no synapsis or crossing over between the X and Y, the sex chromosomes of M. arvalis are of normal size: the X chromosome is of an "original" X size and the Y is a small acrocentric. C-band studies of M. arvalis mitotic metaphase reveal no blocks of heterochromatin on the sex chromosomes. The implications of these findings are discussed.

Animals↗
PubMed1988

Aberrant chromosomal sex-determining mechanisms in mammals, with special reference to species with XY females.

Both mouse and man have the common XX/XY sex chromosome mechanism. The X chromosome is of original size (5-6% of female haploid set) and the Y is one of the smallest chromosomes of the complement. But there are species, belonging to a variety of orders, with composite sex chromosomes and multiple sex chromosome systems: XX/XY1Y2 and X1X1X2X2/X1X2Y. The original X or the Y, respectively, have been translocated on to an autosome. The sex chromosomes of these species segregate regularly at meiosis; two kinds of sperm and one kind of egg are produced and the sex ratio is the normal 1:1. Individuals with deviating sex chromosome constitutions (XXY, XYY, XO or XXX) have been found in at least 16 mammalian species other than man. The phenotypic manifestations of these deviating constitutions are briefly discussed. In the dog, pig, goat and mouse exceptional XX males and in the horse XY females attract attention. Certain rodents have complicated mechanisms for sex determination: Ellobius lutescens and Tokudaia osimensis have XO males and females. Both sexes of Microtus oregoni are gonosomic mosaics (male OY/XY, female XX/XO). The wood lemming, Myopus schisticolor, the collared lemming, Dirostonyx torquatus, and perhaps also one or two species of the genus Akodon have XX and XY females and XY males. The XX, X*X and X*Y females of Myopus and Dicrostonyx are discussed in some detail. The wood lemming has proved to be a favourable natural model for studies in sex determination, because a large variety of sex chromosome aneuploids are born relatively frequently. The dosage model for sex determination is not supported by the wood lemming data. For male development, genes on both the X and the Y chromosomes are necessary.

Animals↗
PubMed1987

Chromosome analysis of human oocytes recovered from preovulatory follicles in stimulated cycles.

To investigate the incidence and types of abnormalities of chromosome number in oocytes, we recovered preovulatory oocytes from 17 women who were undergoing clomiphene stimulation and laparoscopy because of infertility. Twenty-three oocytes were recovered and studied after they had been fixed with a gradual-fixation method: 17 of the oocytes had numbers of chromosomes in the haploid range (19 to 25 second-metaphase chromosomes), 4 had only 1 to 5 chromosomes, 1 was not analyzable, and 1 had 23 chromosome bivalents in the first metaphase. Of the oocytes with chromosome numbers in the haploid range, nine had an apparently normal haploid set of 23 chromosomes. Two had 1 to 2 additional chromosomes, three lacked 2 to 4 chromosomes, and three had totals of chromosomes that were close to 23 but could not be determined with certainty. We conclude that infertile women undergoing clomiphene stimulation have a high proportion (nearly 50 percent) of oocytes with an abnormal karyotype. If this is also true of fertile women, including those not taking clomiphene, it may explain the high frequency of chromosome aberrations occurring in early spontaneous abortion and the low pregnancy rate after in vitro fertilization.

Abortion, Spontaneous↗
PubMed1987

Steroid sulphatase levels are higher in males than in females of the root vole (Microtus oeconomus). Yet another rodent with an active Y-linked allele?

Steroid sulfatase (STS; EC 3.1.6.2) levels were assayed in cultured fibroblasts of root voles captured in the wild. Four independent experiments were performed using two different substrates (DHEAS and E1S). Evidence is presented that in this species, STS levels are significantly higher in males than in females (ratio 1.6:1). We discuss our findings on a comparative basis and suggest that in the root vole the STS gene(s) is X- and Y-linked (as in the mouse) and that it is subject to X-inactivation, or partially so, on one of the X chromosomes in the female.

Alleles↗
PubMed1987

Chromosome analysis of human oocytes failing to cleave after insemination in vitro.

Seventy-six human oocytes lacking signs of fertilization 48 h after insemination in vitro were fixed for chromosome analysis. Only one out of 61 oocytes showed mitotic chromosomes indicating fertilization. Thus, non-cleavage is almost synonymous with non-fertilization. Chromosomes in second meiosis were found in 60 oocytes, of which 52 (86.7%) were analysable. Of these, only 18 (34.6%) displayed an apparently normal 23,X karyotype. Fifteen preparations showed no chromosomes at all but some contained small nuclei, most likely due to degeneration. An earlier stage of degeneration could be represented by a group of second meiosis oocytes (20.0%) carrying between 10 and 18 chromosomes. The large proportion of chromosome abnormalities in this sample might have been due to the fact that the oocytes were unfertilized and perhaps that abnormal oocytes had matured due to ovarian stimulation.

Adult↗
PubMed1987

Ploidy in human cleavage stage embryos after fertilization in vitro.

Chromosome preparations were made from 15 cleaved human embryos in the 2- to 12-cell stage after in-vitro fertilization. All showed two pronuclei before the first cleavage. Twelve had at least one diploid metaphase, while three had interphase nuclei only. There was no evidence of parthenogenetic haploid cleavage. As expected, the frequency of metaphases increased with duration of colchicine treatment: 25 and 55% of the cells reached metaphase after 6-13 and 16-24 hours' treatment, respectively. Cleaved embryos with 'ideal' blastomere numbers (2, 4 or 8) showed a considerably higher metaphase frequency than others. For a more detailed chromosome analysis the technique will have to be further improved. The asynchronous cleavage of blastomeres makes optimal treatment by mitogens difficult.

Adult↗
PubMed1987

Relationship between nucleoli and sex chromosomes during meiosis of the male wood lemming Myopus schisticolor: a fine-structure study.

Electron microscopy of ultrathin serial sections has been used to study the origin and fate of a mass of fibrillar material (FM) during spermatogenesis in the wood lemming Myopus schisticolor. In the course of early pachytene, one of the two nucleoli completely disappears. The remaining nucleolus loses its granular portion and acquires a "round body" encased by the fibrillar moiety, and the restructuring is accompanied by the appearance of FM in the close vicinity of this nucleolus. During diakinesis, the FM increases in volume and density and selectively infiltrates the chromatin of the XY pair. The intermingling of sex chromosomes and FM is at its maximum in metaphase I, giving the XY chromatin a patchy appearance. The FM separates along with the chromatin during the ensuing anaphase I and is shed from the chromosomes during early telophase I. By the time the nuclear envelope is reconstituted, the FM is completely separated from the chromatin. It disintegrates in the spermatids. The FM could not be stained using the Ag-NOR technique. In the wood lemming, X and Y chromosomes show an end-to-end association without a detectable synaptonemal complex. The FM may contribute to the attachment of the two sex chromosomes to each other. Thus, the FM is considered to be a substitute for a chiasma, which normally guarantees proper segregation in anaphase I.

Animals↗
PubMed1987

Chromosome preparations in the field from mammals long after death.

Chromosome preparations of high quality can be obtained from bone marrow cells of small mammals that have been dead for 20 hr or longer. The bone marrow is rinsed out of the femurs with RPMI medium supplemented with 15% fetal calf serum. Add 0.05-0.1 ml of a 0.01% colchicine solution to 5 ml of medium-cell suspension. After 1/2-1 hr of colchicine treatment at 37 C the cells are spun down and the supernatant replaced by 5 ml of hypotonic (0.075 M) KCl. After 12 min in the hypotonic solution at 37 C the cells are fixed in methanol:acetic acid 3:1. Air dried preparations are made after repeating the fixation procedure three times and the chromosomes are stained with Giemsa, if required after pretreatment of the preparations for banding, e.g., GTG. Technical hints for field work are given. The technique has proven successful with several species of rodents and shrews.

Animals↗
PubMed1983

Aberrant sex chromosome mechanisms in mammals. Evolutionary aspects.

There are a number of mammalian species with complicated or unknown mechanisms for sex determination. The literature is reviewed with special reference to the origin and evolution of the sex chromosome mechanisms in three species of monotremes and in the following species of rodents: the creeping vole (Microtus oregoni), the mole vole (Ellobius lutescens), the Amami spinous country rat (Tokudaia osimensis), the wood lemming (Myopus schisticolor), the varying lemming (Dicrostonyx torquatus), South American field mice (Akodon sp.), and the short-tailed bandicoot rat (Nesokia indica). Although this is a heterogeneous group with regard to their sex chromosomes, it is striking that among placental mammals only one order, Rodentia, and only two of its subfamilies, Microtinae and Murinae, are represented. Various reasons for this are discussed. Some of these species have proven to be excellent models for studies of fundamental processes involved in sex determination.

Animals↗
PubMed1982

X-linked genes of the H-Y antigen system in the wood lemming (Myopus schisticolor).

H-Y antigen was investigated in 18 specimens representing six different sex chromosome constitutions of the wood lemming (Myopus schisticolor). The control range of H-Y antigen was defined by the sex difference between normal XX females (H-Y negative per definitionem) and normal XY males (H-Y positive, full titer). H-Y antigen titers of the X*Y and X*0 females were in the male control range, while in the X*X and X0 females the titers were intermediary. Data were obtained with two different H-Y antigen assays: the Raji cell cytotoxicity test and the peroxidase-antiperoxidase (PAP) method. Fibroblasts, gonadal cells, and spleen cells were checked. Presence of full titers of H-Y antigen in the absence of testis differentiation is readily explained by the assumption of a deficiency of the gonad-specific receptor of H-Y antigen. Since sex reversal is inherited as an X-linked trait, genes for this receptor are most likely X-linked. The implications of our findings are discussed in connection with earlier findings concerning H-Y antigen in XY gonadal dysgenesis in man and the X0 situation in man and mouse.

Animals↗
PubMed1982

Chromosome changes in workers (smokers and nonsmokers) exposed to automobile fuels and exhaust gases.

The incidence of chromosome changes in men occupationally exposed to automobile fuels and exhaust gases was investigated. Blood samples were taken from the following four groups of 12 men: drivers of diesel-engine trucks, drivers of gasoline-engine trucks, automobile inspectors, and a reference group. The men in the groups were matched with respect to age, smoking habits, and length of time in their respective jobs. Chromosome preparations from lymphocytes were made and analyzed by standardized routine methods, and the frequencies of gaps, breaks, and sister chromatid exchanges were recorded. Statistical analysis of the results gave no evidence for a marked occupational effect, though there remains a grave suspicion that working with diesel motors may cause an increased level of chromosome changes. Smokers showed a significant or near significant increase in breaks, total aberrations, and sister chromatid exchanges over the nonsmokers in three of the groups. An analysis of the data revealed a weak positive correlation between the frequencies of chromosome breaks and sister chromatid exchanges in an individual.

Adult↗