Maternal Chromosome Sets Research Articles

Spontaneous diploidization of maternal chromosome set in ornamental (Koi) common carp ( Cyprinus carpio L.)

Spontaneous diploidization of maternal chromosome set in ornamental (Koi) common carp ( Cyprinus carpio L.)

The evolution of unusual chromosomal systems in coccoids: extraordinary sex ratios revisited

AbstractCoccoids (scale insects) exhibit a wide variety of chromosomal systems. In many species, paternal chromosomes are eliminated from the male germline such that all of a male's sperm transmit an identical set of maternal chromosomes. In such species, an offspring's sex is determined by whether or not paternal chromosomes are inactivated in the egg's cytoplasm after fertilization. This paper presents a model of the evolution of paternal genome loss in coccoids from an ancestral system of XX‐XO sex determination. The model is based on Hamilton's (1967) theory that different genetic elements within the genome have different unbeatable sex ratios. In this model (1) meiotic drive by the X chromosome in XO males causes female‐biased sex ratios; (2) the maternal set of autosomes in males evolves effective sex linkage to exploit X‐drive; and (3) genes expressed in mothers are selected to convert some of their XX daughters into sons. A similar model may explain the evolution of haplodiploidy.

Uncommon chromosomal mosaicism in chorionic villi

Three cases of unusual chromosomal mosaicism are reported for which the cytogenetic data show inconsistent findings between CVS and AC or fetal tissue, and which cannot be explained simply by non-disjunction. For case 1, in CVS the karyotype was 46,XY, whereas lymphocytes and fibroblasts revealed 69,XXY. DNA fingerprinting indicated one paternal and two maternal chromosome sets, the latter most probably due to omission of maternal meiosis II. For case 2, in CVS mos 46,XX/47,XX,+ mar de novo was observed. Amniotic fluid cells had the karyotype 46,XX. The origin of the marker chromosome might be explained by at least two events of unknown order (a somatic chromosome/chromatid deletion and non-disjunction of the homologous chromosome). In case 3 (CVS: mos 46,XY/46,XY,19q+ de novo; amniotic fluid cells, lymphocytes, and fibroblasts: 46,XY), the surplus of chromosome material in 19q+ might be explained on the basis of a somatic translocation. The idea of a chimera is less convincing, as the mosaic finding is restricted to one tissue. Furthermore, there was no hint of a vanishing twin. Hitherto, no case of structural chromosome mosaicism in CVS has been reconfirmed in fetal tissues.

Spontaneous diploidization of maternal chromosome set in ornamental (koi) carp, Cyprinus carpio L.

An unusually high frequency of spontaneous diploidization in a maternal chromosome set (SDM) was discovered in one ornamental carp (koi) female in an experiment on these fish for induced gynogenesis. Spontaneous appearance of diploid embryos in the gynogenetic offspring (intact eggs × irradiated sperm) and appearance of triploids among control fish (intact eggs × intact sperm) obtained from koi female and males of edible carp indicated spontaneous diploidization of maternal chromosomes (SDM). Possible cytological processes causing this phenomenon are discussed.

Optimal thermal shocks for induced diploid gynogenesis in chinook salmon ( Oncorhynchus tshawytscha)

Thermal shock can disrupt meiosis II in fish oocytes, producing embryos with an extra set of maternal chromosomes from the second polar body; such shocks have been used to induce diploid gynogenesis or triploidy with varied success in different salmonid species. We investigated the effect of thermal shocks on the success of inducing diploid gynogenesis in chinook salmon ( Oncorhynchus tshawytscha) oocytes. Different times of initiation (8, 16, and 24 min post-activation) resulted in similar survival. A treatment duration of 20 min resulted in significantly higher gynogen survival to hatch compared to 5 or 15 min, and a 10-min duration resulted in the lowest mean survival. The effect of temperature on induced retention of the second polar body is unclear due to varied results dependent on the maternal egg source; however, the mean survival to hatch for 25°C treatment groups was significantly higher than the mean of 29°C groups.

Hydatidiform mole and HLA. III. HLA‐antigen expression related to genomic origin

In 52 conceptuses with known genomic origin, HLA determination was performed on whole villi and/or stromal cell cultures. In 26 androgenetic, diploid conceptuses, one or two paternal HLA-A,B haplotypes were found; twenty-four triploid conceptuses with two paternal and one maternal chromosome sets showed either one maternal and one paternal haplotype or one/two paternal HLA-A,B haplotypes. Consequently, androgenesis could not be demonstrated by lack of maternal antigens alone. Concomitant expression of three HLA haplotypes was not seen. HLA-A2 was passed on to the conceptus, both in the genetic subgroups and in the entire series, more frequently than expected.

Microtubule configurations during fertilization, mitosis, and early development in the mouse and the requirement for egg microtubule-mediated motility during mammalian fertilization.

Microtubules forming within the mouse egg during fertilization are required for the movements leading to the union of the sperm and egg nuclei (male and female pronuclei, respectively). In the unfertilized oocyte, microtubules are predominantly found in the arrested meiotic spindle. At the time for sperm incorporation, a dozen cytoplasmic asters assemble, often associated with the pronuclei. As the pronuclei move to the egg center, these asters enlarge into a dense array. At the end of first interphase, the dense array disassembles and is replaced by sheaths of microtubules surrounding the adjacent pronuclei. Syngamy (pronuclear fusion) is not observed; rather the adjacent paternal and maternal chromosome sets first meet at metaphase. The mitotic apparatus emerges from these perinuclear microtubules and is barrel-shaped and anastral, reminiscent of plant cell spindles; the sperm centriole does not nucleate mitotic microtubules. After cleavage, monasters extend from each blastomere nucleus. The second division mitotic spindles also have broad poles, though by third and later divisions the spindles are typical for higher animals, with narrow mitotic poles and fusiform shapes. Colcemid, griseofulvin, and nocodazole inhibit the microtubule formation and prevent the movements leading to pronuclear union; the meiotic spindle is disassembled, and the maternal chromosomes are scattered throughout the oocyte cortex. These results indicate that microtubules forming within fertilized mouse oocytes are required for the union of the sperm and egg nuclei and raise questions about the paternal inheritance of centrioles in mammals.

The origin of human triploidy: an integration of qualitative and quantitative evidence.

SUMMARY1. The origins of human triploidy are inferred from marker chromosomes by use of maximum‐ likelihood models applicable to all mammals with a simple XX: X Y sex determination mechanism. The numerical data comprise a compilation from the literature of 323 triploids and two 2N/3N mosaics, nearly all spontaneously aborted.2. In the particular data, at the time of conception, it is estimated that digynic triploidy (two sets of maternal chromosomes) is less common than diandric (two paternal sets), and that dispermy (fertilization by two spermatozoa) exists and is commoner than diplospermy (fertilization by a diploid spermatozoon) as a cause of diandry: the best estimate of the diplospermic contribution is zero. A low viability of XYY conceptuses has been detected and measured, and is an essential factor in all interpretations: one consequence is that ˜ 15 % digynic triploidy at conception would change to ˜ 19 % at the time of scoring conceptuses. The viabilities of XXX and XXY are comparable with one another.3. Inferences about the general population of triploids at conception are based on approximate confidence limits for the estimates. Digyny probably accounts for at most ˜ 41 % of all triploidy (perhaps as little as ˜ 7%). Diandric triploidy forms a major class (˜ 59‐˜ 93%) attributable at least in part to dispermy. The best estimate of diplospermic triploidy is zero, but it could account for up to ˜ 20 % of all triploids and up to ˜ 31 % of all diandric triploids. The low viability of XYY triploids remains marked as a population characteristic.4. Certain items of indicative ‘ancillary evidence’ are used minimally, primarily as independent checks of the analytical results. They are: (a) that XYY have a low viability, (b) XXX and XXY have a comparable viability, (c) diplospermy plays little or no part in the genesis of triploidy, (d) some triploids are dispermic, (e) F‐body studies can estimate the relative numbers of XX, XY and YY diploid spermatozoa, (a), (b) and (d) are predicted correctly when (c) is used to guide analysis: (a), (c) and (d) when (b) and (e) are so used. This gives some confidence in the validity of the analyses, and in the reality of phenomena established from both qualitative and quantitative evidence.5. The bulk of human triploidy probably arises near the time of fertilization.

Radiation-induced translocations in inseminated eggs of Drosophila melanogaster

The induction of reciprocal translocations by X-irradiation (500 R) of freshly laid inseminated eggs of Drosophila melanogaster was studied. In such eggs the maternal and paternal chromosome sets are exposed while they are within the same cell but in spatially separated nuclei. A constant rate of 0.3% translocations within the maternal chromosome set was found throughout the period during which the maternal genome passes from meiotic metaphase I to the pronuclear stage. During the same period the sperm head, containing the paternal chromosome set, transforms into the paternal pronucleus. At the beginning of this transformation a rate of 2.3% translocations within the paternal chromosome set was found. This rate fell, with the progression towards the pronuclear stage, to about 0.2%. From the recovery of three maternal-paternal translocations it was estimated that the maximal rejoining time of chromosome breaks was on the order of 10 min.