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At least 37 records · Page 2Linked to original sources
PubMed1978

Problems in estimating non-disjunction rate from the F-bodies of two-headed human spermatozoa.

The F-bodies of two-headed human spermatozoa offer a unique potential for estimating non-disjunction rate of the Y chromosome. But there is an unexplained quantitative discrepancy: a gross deficiency of two-headed spermatozoa with no F-bodies, relative to the numbers with one F-body in each head. Any estimation of non-disjunction rate would be overshadowed by this and other major factors. Two-headed spermatozoa cannot be regarded as a random aggregation of haploid heads in pairs. DNA measurements confirmed that each head of 25 normal-sized two-headed spermatozoa was haploid. The distribution of F-body classes is independent of whether sperm tails are single or double. Donors with an exceptionally high incidence of two-headed spermatozoa exist.

Genetics, Medical↗
PubMed1975

Latency differences to monochromatic stimuli measured by disjunctive reaction time.

Two studies were done in order to assess the effects of wavelength on visual perceptual latency as measured in a disjunctive RT paradigm. The results of the first study, though not statistically significant, suggested a trend toward shorter RT to longer wavelength stimuli. In the second study, using well-practiced subjects, significant differences were found between disjunctive RT to red and green stimuli. The results suggest that latency differences as a function of wavelength are demonstrable in an experimental situation in which the subject must react to chromatic information, as differentiated from brightness information.

Adult↗
PubMed1977

Somatic pairing and meiotic nonrandom disjunction in a pericentric inversion of Hylemya antiqua (Meigen).

An asymmetrical pericentric inversion in the onion fly, Hylemya antiqua was studied. Somatic pairing was studied in young eggs from test-and sibcrossed inversion heterozygous females which gave four and seven distinguishable karyotypes respectively. From these seven, three are balanced: the normal type, the inversion heterozygote and homozygote, and four are unbalanced recombinant karyotypes descending from crossovers in the loop. In all types at all mitotic stages the centromeres are paired. The telomeres only show association during prophase but this decreases from mid to late prophase. Quantitative analysis of the four different crossover products as produced by inversion heterozygous females showed the presence of nonrandom disjunction. A significant disparity was observed, viz. the normal chromosome was taken up preferentially into the functional gamete compared to the inverted chromosome. Dragging of long chromatids in the asymmetric dyad during M I-A I is a possible explanation of this feature.

Animals↗
PubMed1979

Stress analysis of disjunct removable partial dentures.

The (1) tooth-supported, (2) ridge-supported, and (3) tooth- and ridge-supported variations of the disjunct removable partial denture were studied. When testing loads were applied to three sites, bilaterally and unilaterally, it was found that the stresses were highest when the removable partial framework was tooth-support. No significant difference was recorded between the ridge-supported partial denture and the tooth- and ridge-supported partial framework. Further refinement of the pinsleeve mechanism may be necessary to effect better control over the distributions of the stresses.

Alveolar Process↗
PubMed1979

A first exploration of a Robertsonian translocation heterozygote in the mouse for its usefulness in cytological evaluation of radiation-induced meiotic autosomal non-disjunction.

In this report some data concerning the male meiotic system of mice heterozygous for Rb(11.13)4Bnr are presented and compared with those of a chromosomally normal Swiss random-bred stock. Change of the genetic background from a C3H/Swiss hybrid situation to the fourth backcross generation (to the Swiss random-bred stock), did not alter the average frequency of aneuploid secondary spermatocytes. This was confirmed by studies on post-implantation loss. Spermatogenic characteristics of Rb4/+ mice, such as testis weight, sperm production and the number of diplotene-metaphase-I figures found in stage XII of the seminiferous epithelium, suggest delay and cell death during this period. These data support our working hypothesis that such an aberrant chromosome system may be more prone to radiation effects and therefore is promising in our cytological studies into the causes of spontaneous and in our cytological studies into the causes of spontaneous and induced autosomal non-disjunction during meiosis in the mouse.

Animals↗
PubMed1977

Attention and cardiac activity: heart rate responses during a variable foreperiod, disjunctive reaction time task.

A variable foreperiod disjunctive reaction time task was used to evaluate the effects of stimulus discriminability on cardiac activity. In two sessions, 20 male undergraduates received easy or difficult auditory discrimination trials in blocked and random series. In the random session only, when the warning stimulus provided information about the difficulty of the subsequent discrimination, difficult trials were associated with greater foreperiod deceleration. Cardiac accelerations also tended to be greater in the foreperiods of difficult trials. There was an effect of both warning and imperative stimuli on the heart rate of the cycle in which the stimuli occurred which depended on the difficulty of the trial. The results are discussed in terms of the psychological significance of the different heart rate responses.

Attention↗
PubMed1979

Additional pedigree supporting the frequent origin of XXYY from consecutive meiotic non-disjunction in paternal gametogenesis.

A 48,XXYY Sardinian patient, born to a 46,XX mother heterozygous for the Gd Mediterranean mutant, and to a 46,XY father hemizygous for the same mutant, was found to have a mosaic distribution of G6PD(+) and G6PD(-) peripheral red blood cells. The most likely interpretation of this finding is that the propositus is an additional example of an XXYY zygote derived from a consecutive meiotic non-disjunction during paternal gametogenesis.

Adult↗
PubMed1975

Meiotic disjunction in t(14;15)6ca heterozygotes and fate of chromosomally unbalanced gametes in embryonic development.

In heterozygous carriers of the mouse reciprocal translocation T(14;15)6Ca, the frequency of nondisjunction involving the minute marker chromosome was 4.4% in the male and 22.2% in the female. The fate of gametes with unbalanced genomes derived from normal as well as abnormal meiotic disjunction in T6 heterozygotes was investigated on the basis of chromosome counts at metaphase II and karyotype analyses in early postimplantation embryos produced by backcrossing with chromosomally normal animals. Results obtained indicate that meiotic, gametic, and zygotic selection attributable to specific types of chromosomal imbalances is minimal, if any, by the late blastocyst stage. All zygotes with unbalanced genomes, except those with 20 normal pairs plus the minute marker, however, die off in the latter half of pregnancy. Therefore, the increased incidence of translocation trisomics among progeny of female as compared with male heterozygotes reflects the higher incidence of nondisjunction in primary oocytes than in spermatocytes.

Animals↗
PubMed1978

Non-random centromere division: a mechanism of non-disjunction causing aneuploidy?

Early centromere separation was investigated in 12 normal children, 14 patients with Down's syndrome and in 12 patients of children with autosomal trisomies. A significantly non-random centromere division of chromosomes was found in each of the cases. A higher frequency of early separated G chromosomes was observed in Down's syndrome. In 2 mothers of trisomy-18 patients, the early division of chromosomes 18, generally seen in normal individuals, could not be demonstrated. The possible assoication between altered sequence of centromere disision and non-disjunction needs further confirmation.

Aneuploidy↗
PubMed1992

Mutants of the microtubule motor protein, nonclaret disjunctional, affect spindle structure and chromosome movement in meiosis and mitosis.

The Drosophila microtubule motor protein, nonclaret disjunctional (ncd), is required for proper chromosome distribution in meiosis and mitosis. We have examined the meiotic and mitotic divisions in wild-type Drosophila oocytes and early embryos, and the effects of three ncd mutants (cand, ncd and ncdD) on spindle structure and chromosome movement. The ncd mutants cause abnormalities in spindle structure early in meiosis I, and abnormal chromosome configurations throughout meiosis I and II. Defective divisions continue in early embryos of the motor null mutant, cand, with abnormal early mitotic spindles. The effects of mutants on spindle structure suggest that ncd is required for proper meiotic spindle assembly, and may play a role in forming or maintaining spindle poles in meiosis. The disruption of normal meiotic and mitotic chromosome distribution by ncd mutants can be attributed to its role as a spindle motor, although a role for ncd as a chromosome-associated motor protein is not excluded. The ncd motor protein functions not only in meiosis, but also performs an active role in the early mitotic divisions of the embryo.

Animals↗
PubMed1978

Chiasma counts and non-disjunction frequencies in a normal ram and in rams carrying the Massey I (t1) Robertsonian translocation.

Testicular material from a normal ram (54XY), three rams heterozygous (53XYt1) and one ram homozygous (52XYt1t1) for the Massey I (t1) translocation was examined. The autosomal non-disjunction in the normal ram was 2.0% compared to a mean of 6.1% in the heterozygous animals. In the homozygous animal there were adhesions of the tunica vaginalis to the cauda epididymidis and extensive spermatogenic arrest.

Animals↗
PubMed1978

Lack of effect on the chromosomal non-disjunction in aged female mice after low dose X-irradiation.

Karyotypes were determined in 1064 embryos of aged C57/BL mothers. The virgin female mice were irradiated with 0, 4, 8 or 16 R of X-rays, respectively, and placed with young untreated males 5 days after irradiation. 10.5-days old embryos were recovered from the uterus. Aneuploid embryos classified as alive (heart beats observed at the dissection) were 1 monosomic in the control group (496 embryos) and 2 trisomics in the irradiated group (568 embryos). The number of aneuploid embryos classified as dead was 4 trisomic cases in the control group and 3 trisomics in the irradiated group. The data indicate that trisomic embryos are not uncommon in the mouse but are eliminated in post-implantation death. In contrast to the results of Yamamoto et al. the present data do not demonstrate an increased frequency of chromosome abnormalities in embryos of aged mice X-irradiated before mating as compared to non-irradiated ones.

Aging↗