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At least 19 recordsLinked to original sources
PubMed1994

Does diploidy increase the rate of adaptation?

Explanations of the evolution of diploidy have focused on the advantages gained from masking deleterious alleles. Recent theory has shown, however, that masking does not always provide an advantage to diploidy and would never favor diploidy in predominantly asexual organisms. We explore a neglected alternative theory which posits that, by doubling the genome size, diploids double the rate at which favorable mutations arise. Consequently, the rate of adaptation in diploids is presumed to be faster than in haploids. The rate of adaptation, however, depends not only on the rate of appearance of new favorable mutations but also on the rate at which these mutations are incorporated (which depends on the population size and on the dominance of favorable mutations). We show that, in both asexuals and sexuals, doubling the mutation rate via diploidy often does not accelerate the rate of adaptation. Indeed, under many conditions, diploidy slows adaptation.

Adaptation, Physiological↗
PubMed1995

Somatic mutation favors the evolution of diploidy.

Explanation of diploidy have focused on advantages gained from masking deleterious mutations that are inherited. Recent theory has shown that these explanations are flawed. Indeed, we still lack any satisfactory explanation of diploidy in species that are asexual or that recombine only rarely. Here I consider a possibility first suggested by Efroimson in 1932, by Muller in 1964 and by Crow and Kimura in 1965: diploidy may provide protection against somatic, not inherited, mutations. I both compare the mean fitness of haploid and diploid populations that are asexual and investigate the invasion of "diploidy" alleles in sexual populations. When deleterious mutations are partially recessive and somatic mutation is sufficiently common, somatic mutation provides a clear advantage to diploidy in both asexual and sexual species.

Biological Evolution↗
PubMed2003

High sex chromosome aneuploidy and diploidy rate of epididymal spermatozoa in obstructive azoospermic men.

PURPOSE: To evaluate the frequencies of sex chromosome aneuploidy and diploidy rate of epididymal spermatozoa from obstructive azoospermic men and its impact on intracytoplasmic sperm injection (ICSI) outcomes. METHODS: Epididymal spermatozoa retrieved from 24 obstructive azoospermic men and ejaculated spermatozoa from 24 fertile donors were analyzed using triple color fluorescence in situ hybridization (FISH) techniques, in order to investigate the rates of diploidy and aneuploidy for chromosomes 18, X and Y. RESULTS: Epididymal spermatozoa from obstructive azoospermic men had total sex aneuploidy, disomy 18, and diploidy rates significantly higher than ejaculated spermatozoa from normozoospermic fertile controls (1.44% vs 0.14%, 0.11% vs 0.02%, and 0.18% vs 0.02%, respectively; p < 0.005). There were no statistically significant differences in ICSI outcomes between the patients who had high and low epididymal sperm aneuploidy rate. CONCLUSIONS: Epididymal spermatozoa from obstructive azoospermic patients had an elevated sex chromosome aneuploidy and diploidy rate. The increased frequency of chromosomal abnormalities did not have a direct effect on the ICSI outcome.

Aneuploidy↗
PubMed2001

Linear increase of diploidy in human sperm with age: a four-colour FISH study.

The aim of this study was to determine if donor age is associated with an increased incidence of diploidy and of disomy for the sex chromosomes and for chromosomes 6 and 21. We used simultaneous fluorescence in situ hybridisation (FISH) for chromosomes 6, 21, X and Y in sperm from 18 healthy donors, aged 24-74 years (mean 48.8 years). A total of 194 024 sperm were analysed, with a minimum of 10 000 sperm scored for each donor. Our results indicate a significant increase of the level of diploidy (P=0.002), and a marginal significance of total sex chromosome disomy (P=0.055) with age. No increase was observed for disomies XX, YY, XY, 21 or 6. The percentages of increase for disomy and for diploidy ranged from 0.3 to 17% for each 10-year period. Chromosomes 6 and 21 did not segregate preferentially with the X or Y chromosomes. Our findings show a linear trend association between age and diploidy in human males.

Adult↗
PubMed1992

Recombination and the evolution of diploidy.

With two copies of every gene, a diploid organism is able to mask recessive deleterious mutations. In this paper we present the analysis of a two-locus model designed to determine when the masking of deleterious alleles favors the evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases ("alternation of generations"). It is hypothesized that diploidy will be favored whenever masking occurs ("the masking hypothesis"). Using analytical methods, we confirm that this masking hypothesis is essentially correct under free recombination: as long as the heterozygous expression of deleterious alleles is sufficiently masked by the wild-type allele, diploidy is favored over haploidy. When the rate of recombination is lower, however, diploidy is much less likely to be favored over haploidy. In fact, according to our model, the evolution of diploidy is impossible without significant levels of recombination even when masking is fairly strong.

Biological Evolution↗
PubMed2000

Frequency of hyper-, hypohaploidy and diploidy in ejaculate, epididymal and testicular germ cells of infertile patients.

The hypothesis that sperm aneuploidy and diploidy increase as a function of spermatogenesis impairment was addressed. Ejaculated semen samples from a series of men (n = 22) with very low total normal motile count (1 x 10(6)) was analysed in terms of sperm aneuploidy and diploidy by in-situ hybridization and compared with controls (n = 10). Germ cell aneuploidy was also analysed in an additional series of infertile patients presenting unexplained infertility (n = 3), congenital absence of the vas deferens (CAVD) (n = 6) and non-obstructive azoospermia (n = 3) undergoing IVF, microsurgical epididymal sperm aspiration (MESA)/ICSI and testicular sperm extraction (TESE)/ICSI cycles respectively. In-situ hybridization for chromosomes 1, 17, X and Y was performed on ejaculate, epididymal and testicular spermatozoa. Significantly higher sperm aneuploidy and diploidy rates where found (for the four chromosomes analysed) in spermatozoa from oligoasthenoteratozoospermia (OAT) over controls (18 versus 2.28% and 2.8 versus 0.13% respectively; P < 0.001). Testicular germ cells had even higher rates of sperm aneuploidy and diploidy. However, in this group it was difficult to determine whether the cells analysed were dysmorphic spermatozoa or spermatids. The data warrant further investigation on the cytogenetic abnormalities found in most germ cells identified in testicular tissue biopsies of azoospermic patients.

Adult↗
PubMed1999

Screening for abnormalities of chromosomes X, Y, and 18 and for diploidy in spermatozoa from infertile men participating in an in vitro fertilization-intracytoplasmic sperm injection program.

OBJECTIVE: To evaluate the frequency of disomy (for chromosomes X, Y, and 18) and of diploidy in the spermatozoa of infertile men undergoing intracytoplasmic sperm injection (ICSI). DESIGN: Prospective analysis of sperm nuclei by fluorescence in situ hybridization (FISH). SETTING: University-affiliated IVF-ICSI program. PATIENT(S): Semen samples from 19 patients participating in an IVF-ICSI program. INTERVENTION(S): Semen samples were analyzed and prepared for FISH. MAIN OUTCOME MEASURE(S): Semen parameters were evaluated. The frequency of disomy for chromosomes X, Y, and 18 and the frequency of diploidy were analyzed by FISH. RESULT(S): A total of 9,373 spermatozoa from 19 infertile patients were analyzed and compared with spermatozoa from a control group of 5 healthy men. No differences in the frequency of disomy 18 were found, but statistically significant differences in the incidence of sex chromosome disomy and of diploidy were observed. CONCLUSION(S): The study of sperm nuclei by FISH is useful to improve genetic counseling in infertile patients selected for ICSI.

Adult↗
PubMed2002

Diploidy restoration in Wolbachia-infected Muscidifurax uniraptor (Hymenoptera: Pteromalidae).

Thelytokous reproduction, where females produce diploid female offspring without fertilization, can be found in many insects. In some Hymenoptera species, thelytoky is induced by Wolbachia, a group of cytoplasmically inherited bacteria. We compare and contrast early embryonic development in the thelytokous parthenogenetic species Muscidifurax uniraptor with the development of unfertilized eggs of the closely related arrhenotokous species, Muscidifurax raptorellus. In the Wolbachia-infected parasitic wasp M. uniraptor, meiosis and the first mitotic division occur normally. Diploidy restoration is achieved following the completion of the first mitosis. This pattern differs in the timing of diploidy restoration from previously described cases of Wolbachia-associated thelytoky. Results presented here suggest that different cytogenetic mechanisms of diploidy restoration may occur in different species with Wolbachia-induced thelytoky.

Animals↗
PubMed1991

Transition from haploidy to diploidy.

As a direct consequence of sex, organisms undergo a haploid and a diploid stage during their life cycle. Although the relative duration of haploid and diploid phases varies greatly among taxa, the diploid phase is more conspicuous in all higher organisms. Therefore it is widely believed that diploidy offers more evolutionary possibilities and is thus nearly always selected for. We have now performed computer simulations to investigate one possible advantage of diploidy, that is, protection against the expression of deleterious mutations. Instead of comparing isolated haploid and diploid populations, we considered interbreeding haploids and diploids. Diploids invaded the population only when the dominance degree of a single deleterious mutation was smaller than about 1/2, and the condition allowing diploidy to invade depended on how harmful the mutation was.

Alleles↗
PubMed2000

Comparative study of disomy and diploidy rates in spermatozoa of fertile and infertile men: a donor-adapted protocol for multi-colour fluorescence in situ hybridization (FISH).

Spermatozoa from seven healthy donors (two of whom had already fathered children) and five infertile patients taking part in the local programme of intracytoplasmic sperm-injection (ICSI) were investigated for the disomy rates of chromosomes 13/21, 18, X and Y as well as for the diploidy rates. Two- and three-colour fluorescence in situ hybridization (FISH) was applied after a donor-adapted decondensation pre-treatment: in a preliminary decondensation series the optimum fluorescence signals were individually determined by variation of the concentration of the decondensation reagents and the duration of incubation with these reagents. Strict scoring criteria were applied. The average disomy rates ranged from 0.10% (chromosomes 13/21) to 0.44% (disomy XY) in the infertile donors and from 0.07% (disomy XX) to 0.36% (disomy XY) in the controls. The average diploidy rates were 0.22% and 0.20% for the infertile donors and the controls respectively. There was no statistically significant difference between the two groups with respect to the disomy and diploidy rates. Within the two groups there were inter-individual differences which were partly statistically significant, indicating considerable inter-donor variation of the aneuploidy rates.

Aneuploidy↗
PubMed1996

Multicolor fluorescence in situ hybridization analysis of aneuploidy and diploidy frequencies in 225,846 sperm from 10 normal men.

Aneuploidy and diploidy frequencies for chromosomes 1, 12, X, and Y were assessed in 225,846 sperm from 10 normal men. Results from 5 of the men have previously been reported. Multicolor fluorescence in situ hybridization (FISH) was used to control for lack of probe hybridization and to distinguish diploidy from disomy. A minimum of 10,000 sperm per donor were evaluated for each chromosome. Sperm were considered disomic if two fluorescent signals were separated by a distance of a minimum of one signal domain. The mean frequencies of disomic sperm for chromosomes 1 and 12 were 0.11% (range 0.05-0.18%) and 0.16% (range 0.10-0.25%), respectively. The means for the sex chromosomal aneuploidies were 0.07% XX, 0.18% YY, and 0.16% XY, totaling 0.42% for all sex chromosomes (range 0.23-0.71%). The incidence of disomic sperm for the sex chromosomes was significantly increased compared to the frequency for the autosomes, corroborating results obtained from studies of sperm karyotypes and spontaneous abortions. The mean frequencies of single X- and Y-bearing sperm were 50.1% and 49.0%, respectively--not significantly different from 50%. The mean frequency of diploid sperm was 0.16% (0.06-0.42%). Interdonor heterogeneity was found to exist for disomy 1, XX, YY, and diploidy, suggesting significant variation among normal men. Comparison of these FISH results to our historical sperm karyotypes demonstrated that the sex ratios and disomy frequencies for chromosomes 1 and X were similar. However, there was a significantly increased frequency of disomic sperm for chromosomes 12, YY, and XY in FISH data compared with sperm karyotypes. In general, FISH data agreed quite well with values from sperm karyotyping, including the increased frequency of sex chromosomal aneuploidy compared with autosomal aneuploidy in sperm. Multicolor FISH analysis permits an accurate distinction between disomic and diploid sperm and allows analysis of large sample sizes. This powerful technology may be useful for future studies of potential environmental and occupational mutagens.

Adult↗
PubMed2005

Low total normal motile count values are associated with increased sperm disomy and diploidy rates in infertile patients.

This study was undertaken to evaluate the possibility of identifying men at increased risk of sperm aneuploidy and diploidy on the bases of specific cut-off values of the total normal motile count (TNMC). Twenty-seven consecutive, unselected male patients referred to our Unit were studied: 11 patients with normal sperm parameters (group A) suffering from unexplained infertility and 16 infertile patients with abnormal sperm parameters (group B). Disomy rates for chromosomes 1, 4, 8, 12, 18, X and Y were ascertained for each patient by means of triple and double fluorescence in situ hybridization (FISH) experiments. Both univariate and multivariate statistical analyses by principal component analysis (PCA) were performed for comparisons between sperm aneuploidy rates and semen quality (TNMC). TNMC scores in the two groups were significantly different (23.5 x 10(6) and 1.52 x 10(6), in groups A and B, respectively, p = 0.00002). In general, higher sperm disomy rates were noted for all chromosomes in group B compared with group A. Statistical significance was observed for disomy 1, total disomy rate (3.36% vs. 1.38%), and diploidy (0.49% vs. 0.19%) (p < 0.01). For disomy 4 and 8, differences resulted close to significance. PCA clearly showed how independent variables were inter-related. Infertile men with TNMC < 2 x 10(6) (male factor) were found to be at increased risk for sperm aneuploidy and diploidy. Multivariate analysis by PCA resulted as a useful method to visualize the information of the data sets on a bi-dimensional plot considering all the patients and all the variables at the same time.

Adult↗
PubMed2002

Chromosome V loss due to centromere knockout or MAD2-deletion is immediately followed by restitution of homozygous diploidy in Saccharomyces cerevisiae.

To investigate the possibility of inducing specific chromosome loss by centromere deletion in eukaryotic cells, the yeast diploid strain ZG1, carrying three pairs of heterozygous marker genes (CAN1(S)/can1(R), URA3/Deltaura3, hphMX4/HIS1), widely spread on both arms of chromosome V, was constructed. One of the two centromeres V of ZG1 was replaced by the LEU2 gene via the well-established PCR-mediated knockout technique. After DNA transformation, putative yeast colonies that showed loss of heterozygosity (LOH) for the three markers of chromosome V (CAN1(S) URA3 hphMX4) were identified among the colonies selected for leucine prototrophy. Phenotypic tests, colony-PCR and Southern blot analysis of these cells demonstrated the physical loss of the CAN1(s), URA3, and hphMX4 marker genes from the genome. Further tetrad analysis results were consistent with this conclusion; however, four-spore viability indicated a normal chromosome number of these transformants. To verify the diploidy of the selected chromosome V, the HIS1 gene was deleted with a standard KanMX4 knockout DNA cassette. The resulting heterogeneity of the HIS1/KanMX4 markers, together with quantitative PCR and densitometric analysis on chromosome V, confirmed its diploid complement, thereby indicating that an endoreduplication event had taken place. Restitution of diploidy also occurred in MAD2-deleted strains undergoing higher rates of spontaneous chromosome V loss, indicating a more general phenomenon that is undetectable by phenotypic analysis alone.

Calcium-Binding Proteins↗
PubMed1986

High susceptibility for diploidy in ovulated oocytes from XO mice.

Adult female mice of the "sensitive" NMRI/Han strain ovulate diploid oocytes after gonadotropin treatment. Other mouse strains are "non-sensitive" with respect to the ovulation of such diploid oocytes. In this study we combined the impaired ovarian situation in the XO karyotype with the trait "diploidy", which is determined genetically, by mating Ta/O (Ta = Tabby) females of C3H X 101 background to males of the NMRI/Han strain. The adult female F1 hybrids were stimulated to ovulation by gonadotropins and identified by their karyotype (XX or XO). The cytogenetic analysis of ovulated oocytes revealed a low level of diploidy in the XX littermates (1.0%), but a very high level in females with the XO karyotype (24.6%). All of the XO females ovulated at least one diploid oocyte. We suggest that it is the XO status which drastically impairs meiosis I in our "gonadotropin-sensitive" F1 females due to (1) alterations of the developmental program within the oocyte, (2) a disturbed communication between oocyte and follicle, (3) a preferential maturation and ovulation of "follicles at risk", or (4) an exceptional recruitment of many such follicles, by, e.g., a premature responsiveness to gonadotropins in our XO females. An interdependence of several such mechanisms is possible.

Animals↗
PubMed1984

Control of meiosis by somatic cells in mice: inheritance of the meiosis I error 'diploidy' and nonexpression in sensitive NMRI/Han oocytes ovulated from chimeras.

NMRI mouse and Djungarian hamster females ovulate diploid and/or hyperploid oocytes with increased frequencies after gonadotrophin stimulation, suggesting that somatic cells are involved in the failures of endocrine control resulting in aneuploidy. To study the inheritance of gonadotrophin-induced aneuploidy as well as the fate of sensitive oocytes in a resistant somatic environment and vice versa, we analysed the frequency of diploid oocytes in NMRI/Han, C57BL/6J and their F1 hybrids (C57BL/6J X NMRI/Han), (NMRI/Han X C57BL/6J) as well as in NMRI/Han in equilibrium C57BL/6J chimeric females after gonadotrophin injections. Ovulated oocytes were analysed in all females for the appearance of diploidy, characterized as premature arrest of development at metaphase I. Our data suggest that the trait of induced diploidy is genetically determined and can be transmitted either maternally or paternally. A maternal effect modulated the expression of that trait. Several mechanisms acting on the feed-back control ovary-hypothalamus/pituitary, within the ovary or even within a chimeric follicle, may be responsible that 'sensitive' oocytes ovulated from chimeras are all normal haploid. These data suggest that not only oocyte maturation but also chromosome disjunction during meiosis I is controlled by somatic cells.

Aneuploidy↗
PubMed1998

Aneuploidy and diploidy rates in sperm of five men after three-colour hybridization: indication of X chromosome-associated autosome 2 aneuploidy.

The frequencies of aneuploidy and diploidy for chromosomes 2, X and Y in sperm nuclei of five nonsmoking normal donors were assessed by three-colour fluorescence in situ hybridization. We detected neither significant interindividual variability nor age effect (age range of the study group: 26-38 yr) on the mean frequencies of aneuploid and diploid sperm. Nullisomic sperm were observed more frequently than disomic sperm. In addition, sex chromosomal meiotic nondisjunction occurred at a higher rate than autosomal nondisjunction, and disomic sperm for the sex chromosomes were formed mainly by errors in the second meiotic division. Our data indicate that diploidy occurs at a very low frequency in comparison with aneuploidy. Furthermore, the overall proportion of X-bearing sperm nuclei aneuploid for chromosome 2 is significantly higher than that of Y-bearing sperm (0.14% vs. 0.05%, respectively; p < 0.001). This finding adds further evidence that autosomal aneuploidy can be preferentially associated with the presence of one of the two gonosomes.

Adult↗
PubMed1974

Population studies in microorganisms. I. Evolution of diploidy in Saccharomyces cerevisiae.

The relative adaptation of isogenic haploid and diploid strains of yeast was investigated in different sets of physiological conditions. When all nutrients were present in excess, no difference in the reproductive rates of isogenic haploid and diploid strains of yeast was detected in both optimal and non-optimal growth conditions. Competition between haploid and diploid strains of yeast was observed when growth was limited by the concentration of a single nutrilite. Under certain conditions when fitness (reproductive rate) is determined by transport of an essential nutrilite that exists in very low concentrations, diploid cells were selected against. These environmental conditions are similar to those found in offshore marine environments where nutrients are often present in extremely low concentrations. The fitness of diploid cells was estimated to be.93 +/-.02 (haploid fitness = 1). The reduced fitness of diploid cells in this environment can be explained by the reduced surface area/volume ratio possessed by diploid cells in comparison to haploid cells. The fitnesses of haploid and diploid cells in these environments are closely correlated with geometric variations in these strains. These results are consistent with the hypothesis that diploid cells are simply double haploids, and diploidy per se does not confer any direct adaptive advantage. The mechanism of the evolution of diploidy as a dominant phase in the life cycle of higher plants and animals remains obscure.

Diploidy↗
PubMedDate not supplied

Genetic error, sex, and diploidy.

Mathematical models and experiments on transformation are reported testing the hypothesis that sex and diploidy evolved as a DNA repair system. The models focus on the origin of diploidy and sex by studying selection between asexual haploids, sexual haploids, and diploids. Haploid cells are efficient replicators, while diploid cells are resistance to damage. A sexual haploid may combine the advantages of both: spending much of its life cycle in the haploid state, then temporarily fusing to become diploid, followed by splitting to the haploid state. During the diploid state DNA damage can be repaired, since there are two copies of the gene in the cell and one copy is presumed to be undamaged. Five basic rate parameters are employed: birth and death; genomic damage (for the haploids alone); and, for the sexual cell, fusion and splitting. Parameter space bifurcation diagrams for the equilibria are drawn, and solutions of the equations are described in terms of these diagrams. Each type of cell has a region of the parameter space that it occupies exclusively (given its initial presence in the competition). The haploid wins in environments characterized by low damage. The diploid wins in environments characterized by high damage, low mortality, and abundant resources. In general, only a single type of cell occupies a given portion of the space. We find, however, that competitive coexistence of an asexual diploid and sexual haploid is possible in spite of the fact that they are competing for a single resource (nucleotide building blocks). Sex can increase from rarity if matings occur with asexual cells. Only sex can cope with both high mortality and high damage. We then turn to natural bacterial transformation as a model system for the experimental study of sex. Natural transformation in distributed widely, but apparently sparsely, in all bacterial groups. A very preliminary phylogenetic analysis of the bacilli and related species indicates that transformation is probably not a diversifying force in bacterial evolution. However, it is difficult to be sure because of the ambiguity surrounding negative data. Experiments with the bacterium Bacillus subtilis indicate that transformation frequencies respond adaptively to DNA damage if homologous donor DNA is used. Several specific hypotheses for this response are considered. Recent work in other labs on the evolution of transformation is discussed from the point of view of the hypothesis that transformation functions in DNA repair.

DNA Repair↗