CHROMOSOMES OF THE MEXICAN PLATEAU MOUSE, PEROMYSCUS MELANOPHRYS, AND A NEW SEX DETERMINING MECHANISM IN MAMMALS

1974 ◽  
Vol 16 (4) ◽  
pp. 797-804 ◽  
Author(s):  
Earl G. Zimmerman
Keyword(s):  
Y Chromosome ◽  
X Chromosome ◽  
Diploid Number ◽  
Chromosomal Analysis ◽  
X Chromosomes ◽  
Unique Type ◽  
Chromosomal Difference ◽  
Males And Females

A chromosomal analysis of 86 specimens of Peromyscus melanophrys reveals a unique type of chromosomal difference between males and females Females possess three large pairs of subtelocentric autosomes, two pairs of small submetacentric autosomes, and 18 pairs of acrocentric autosomes. The X chromosomes are also subtelocentric. Males possess a similar karyotype with a subtelocentric X chromosome, a minute Y chromosome, and two unmatched autosomes, a large subtelocentric and a large acrocentric. Both sexes have a diploid number of 48. Studies from meiosis and autoradiography indicate that a portion of the original Y chromosome has been translocated to an autosome resulting in a new multiple sex determining mechanism in mammals, an X1X1X2X2/X1X2Y1Y2 system.

The Chromosomal Cytology of Bisexual and Parthenogenetic Calligrapha spp. (Coleoptera: Chrysomelidae)

1964 ◽  
Vol 96 (1-2) ◽  
pp. 144-144
Author(s):  
J. G. Robertson
Keyword(s):  
Y Chromosome ◽  
X Chromosome ◽  
Diploid Number ◽  
Testicular Tissue ◽  
Reduction Division ◽  
Bisexual Species ◽  
X Chromosomes ◽  
Metaphase I

Thirty-one geographic entities comprising 17 species of Calligrapha were examined cytologically. In the bisexual species rowena, philadelphica, pnirsa, amator, alni, confluens, californica, bidenticola, multipunctata, verrucosa, and pruni, the diploid number of chromosomes was 23 in males and 24 in females. The sex mechanism consisted of a single X chromosome in males and two X chromosomes in females. No Y chromosome was present. During reduction division in testicular tissue 11 bivalents were formed and a single heterochromatic X chromosome lay to one side of the bivalents which showed congression at metaphase I. The basic chromosomal formula 11 + XO can therefore be assigned to this group. The formula is modified in some populations according to the following circumstances.

Clues from other animals and theoretical considerations

Development ◽  
1987 ◽  
Vol 101 (Supplement) ◽  
pp. 3-4
Author(s):  
Anne McLaren
Keyword(s):  
Sex Determination ◽  
Genetic Control ◽  
Y Chromosome ◽  
X Chromosome ◽  
X Chromosomes ◽  
The Third ◽  
Mouse Species ◽  
Primary Male ◽  
Theoretical Considerations ◽  
State Of Activity

In the first two papers of this volume, the genetic control of sex determination in Caenorhabditis and Drosophila is reviewed by Hodgkin and by Nöthiger & Steinmarin-Zwicky, respectively. Sex determination in both cases depends on the ratio of X chromosomes to autosomes, which acts as a signal to a cascade of règulatory genes located either on autosomes or on the X chromosome. The state of activity of the last gene in the sequence determines phenotypic sex. In the third paper, Erickson & Tres describe the structure of the mouse Y chromosome and the polymorphisms that have been detected in different mouse species and strains. As in all mammals, the Y carries the primary male-determining locus; autosomal genes may also be involved in sex determination, but they must act down-stream from the Y-linked locus.

scholarly journals A second X chromosome contributes to resilience in a mouse model of Alzheimer’s disease

2020 ◽  
Vol 12 (558) ◽  
pp. eaaz5677 ◽  
Author(s):  
Emily J. Davis ◽  
Lauren Broestl ◽  
Samira Abdulai-Saiku ◽  
Kurtresha Worden ◽  
Luke W. Bonham ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Y Chromosome ◽  
X Chromosome ◽  
Sex Chromosome ◽  
Testicular Development ◽  
X Chromosomes ◽  
Model Of Alzheimer’S Disease ◽  
Preclinical Ad ◽  
Brain Expression

A major sex difference in Alzheimer’s disease (AD) is that men with the disease die earlier than do women. In aging and preclinical AD, men also show more cognitive deficits. Here, we show that the X chromosome affects AD-related vulnerability in mice expressing the human amyloid precursor protein (hAPP), a model of AD. XY-hAPP mice genetically modified to develop testicles or ovaries showed worse mortality and deficits than did XX-hAPP mice with either gonad, indicating a sex chromosome effect. To dissect whether the absence of a second X chromosome or the presence of a Y chromosome conferred a disadvantage on male mice, we varied sex chromosome dosage. With or without a Y chromosome, hAPP mice with one X chromosome showed worse mortality and deficits than did those with two X chromosomes. Thus, adding a second X chromosome conferred resilience to XY males and XO females. In addition, the Y chromosome, its sex-determining region Y gene (Sry), or testicular development modified mortality in hAPP mice with one X chromosome such that XY males with testicles survived longer than did XY or XO females with ovaries. Furthermore, a second X chromosome conferred resilience potentially through the candidate gene Kdm6a, which does not undergo X-linked inactivation. In humans, genetic variation in KDM6A was linked to higher brain expression and associated with less cognitive decline in aging and preclinical AD, suggesting its relevance to human brain health. Our study suggests a potential role for sex chromosomes in modulating disease vulnerability related to AD.

Review Lecture: Mechanisms and evolutionary origins of variable X-chromosome activity in mammals

1974 ◽  
Vol 187 (1088) ◽  
pp. 243-268 ◽  
Keyword(s):  
X Chromosome ◽  
Germ Cells ◽  
Gene Dosage ◽  
Control Mechanisms ◽  
Compensation Mechanism ◽  
X Chromosomes ◽  
Animal Group ◽  
Evolutionary Origins ◽  
Genetic Activity ◽  
Males And Females

The X-chromosome of mammals is remarkable for its variable genetic activity. In somatic cells only a single X-chromosome is active, no matter how many are present, thus providing a dosage compensation mechanism by which males and females effectively have the same gene dosage of X-linked genes. In germ cells, however, it appears that all X-chromosomes present are active. Female germ cells require the presence of two X-chromosomes for normal survival, whereas male germ cells die if they have more than one X-chromosome. This system is found in all eutherian mammals and in marsupials, but is not known in any other animal group. In marsupials the X-chromosome derived from the father seems to be preferentially inactivated, whereas in eutherian mammals that from either parent may be so in different cells of the same animal. The differentiation of a particular X-chromosome as active or inactive is initiated in early embryogeny, and thereafter maintained through all further cell divisions in that individual. The mechanisms by which this is achieved are of great interest in relation to genetic control mechanisms in general. Various recent hypotheses concerning these mechanisms are discussed.

scholarly journals Signatures of replication timing, recombination, and sex in the spectrum of rare variants on the human X chromosome and autosomes

2019 ◽  
Vol 116 (36) ◽  
pp. 17916-17924 ◽  
Author(s):  
Ipsita Agarwal ◽  
Molly Przeworski
Keyword(s):  
X Chromosome ◽  
Rare Variants ◽  
Low Frequency ◽  
Replication Timing ◽  
Double Strand Breaks ◽  
X Chromosomes ◽  
Strand Breaks ◽  
Biochemical Processes ◽  
Males And Females ◽  
Mutational Processes

The sources of human germline mutations are poorly understood. Part of the difficulty is that mutations occur very rarely, and so direct pedigree-based approaches remain limited in the numbers that they can examine. To address this problem, we consider the spectrum of low-frequency variants in a dataset (Genome Aggregation Database, gnomAD) of 13,860 human X chromosomes and autosomes. X-autosome differences are reflective of germline sex differences and have been used extensively to learn about male versus female mutational processes; what is less appreciated is that they also reflect chromosome-level biochemical features that differ between the X and autosomes. We tease these components apart by comparing the mutation spectrum in multiple genomic compartments on the autosomes and between the X and autosomes. In so doing, we are able to ascribe specific mutation patterns to replication timing and recombination and to identify differences in the types of mutations that accrue in males and females. In particular, we identify C > G as a mutagenic signature of male meiotic double-strand breaks on the X, which may result from late repair. Our results show how biochemical processes of damage and repair in the germline interact with sex-specific life history traits to shape mutation patterns on both the X chromosome and autosomes.

scholarly journals FITNESS EFFECTS OF EMS-INDUCED MUTATIONS ON THE X CHROMOSOME OF DROSOPHILA MELANOGASTER. I. VIABILITY EFFECTS AND HETEROZYGOUS FITNESS EFFECTS

Genetics ◽  
1977 ◽  
Vol 87 (4) ◽  
pp. 763-774
Author(s):  
Joyce A Mitchell
Keyword(s):  
Drosophila Melanogaster ◽  
X Chromosome ◽  
Strongly Correlated ◽  
Induced Mutations ◽  
X Chromosomes ◽  
Heterozygous Condition ◽  
Fitness Effects ◽  
Sucrose Solutions ◽  
Discrete Generation ◽  
Males And Females

ABSTRACT Drosophila melanogaster X chromosomes were mutagenized by feeding males sucrose solutions containing ethyl methanesulfonate (EMS); the concentrations of EMS in the food were 2.5 mm, 5.0 mm, and 10.0 mm. Chromosomes were exposed to the mutagen up to three times by treating males in succeeding generations. After treatment, the effective exposures were 2.5, 5.0, 7.5, 10.0, 15.0, and 30.0 mm EMS. X chromosomes treated in this manner were tested for effects on fitness in both hemizygous and heterozygous conditions, and for effects on viability in hemizygous and homozygous conditions. In addition, untreated X chromosomes were available for study. The viability and heterozygous fitness effects are presented in this paper, and the hemizygous fitness effects are discussed in the accompanying one (Mitchell and Simmons 1977). Hemizygous and homozygous viability effects were measured by segregation tests in vial cultures. For hemizygous males, viability was reduced 0.5 percent per mm EMS treatment; for homozygous females, it was reduced 0.7 percent per mm treatment. The decline in viability appeared to be a linear function of EMS dose. The viabilities of males and females were strongly correlated. Heterozygous fitness effects were measured by monitoring changes in the frequencies of treated and untreated X chromosomes in discrete generation populations which, through the use of an X-Y translocation, maintained them only in heterozygous condition. Flies that were heterozygous for a treated chromosome were found to be 0.4 percent less fit per m m EMS than flies heterozygous for an untreated one.

Mapping the SRY gene in Microtus cabrerae: a vole species with multiple SRY copies in males and females

Genome ◽  
2002 ◽  
Vol 45 (3) ◽  
pp. 600-603 ◽  
Author(s):  
Rosa Fernández ◽  
María José L Barragán ◽  
Mónica Bullejos ◽  
Juan Alberto Marchal ◽  
Sergio Martínez ◽  
...  
Keyword(s):  
Y Chromosome ◽  
X Chromosome ◽  
Heterochromatic Region ◽  
Pericentromeric Region ◽  
Specific Gene ◽  
Sry Gene ◽  
Microtus Cabrerae ◽  
Gene Copies ◽  
Vole Species ◽  
Males And Females

The SRY gene is a single-copy, male-specific gene, located on the Y chromosome in most mammals. However, recently we have described the presence of multiple polymorphic copies of this gene in both males and females of the vole species Microtus cabrerae. Here, we present the chromosomal localization of SRY gene copies in this species by fluorescent in situ hybridization (FISH). This technique localized these gene copies in the short arm, and hence in the euchromatic region, of the Y chromosome. Furthermore, several copies of the SRY gene are located on the X chromosome. These copies are spread along the entire heterochromatic region of the X chromosome, occupying the whole short arm, the centromeric region, and the pericentromeric region of the long arm.Key words: FISH mapping, Micotus cabrerae, SRY gene, X chromosome, Y chromosome.

scholarly journals Sex-chromosome Mosaicism in the Lemur-like Possum Hemibelideus lemuroides (Marsupialia: Petauridae)

1984 ◽  
Vol 37 (3) ◽  
pp. 131 ◽  
Author(s):  
GM McKay ◽  
LR McQuade ◽  
JD Murray ◽  
SR von Sturmer
Keyword(s):  
Bone Marrow ◽  
Y Chromosome ◽  
Sex Chromosome ◽  
Bone Marrow Cells ◽  
Regular System ◽  
Somatic Tissue ◽  
Fibroblast Cells ◽  
X Chromosomes ◽  
Chromosome Mosaicism ◽  
Males And Females

A regular system of sex chromosome mosaicism in a somatic tissue is reported in H. lemuroides. Spermatogonial mitosis and cultured fibroblast cells are 2n = 20, while most bone marrow cells from both males and females are 2n = 19. In males the Y chromosome is lost and in females one of the X chromosomes.

scholarly journals Xist spatially amplifies SHARP recruitment to balance chromosome-wide silencing and specificity to the X chromosome

2021 ◽  
Author(s):  
Joanna W Jachowicz ◽  
Mackenzie Strehle ◽  
Abhik K Banerjee ◽  
Mario R Blanco ◽  
Jasmine Thai ◽  
...  
Keyword(s):  
Gene Silencing ◽  
X Chromosome ◽  
Target Genes ◽  
General Mechanism ◽  
X Chromosomes ◽  
Xist Rna ◽  
Mammalian Genomes ◽  
Males And Females ◽  
Amplification Mechanism ◽  
Low Levels

Although thousands of lncRNAs are encoded in mammalian genomes, their mechanisms of action are largely uncharacterized because they are often expressed at significantly lower levels than their proposed targets. One such lncRNA is Xist, which mediates chromosome-wide gene silencing on one of the two X chromosomes to achieve gene expression balance between males and females. How a limited number of Xist molecules can mediate robust silencing of a significantly larger number of target genes (~1 Xist RNA: 10 gene targets) while maintaining specificity to genes on the X within each cell is unknown. Here, we show that Xist drives non-stoichiometric recruitment of the essential silencing protein SHARP (also called Spen) to amplify its abundance across the inactive X, including at regions not directly occupied by Xist. This amplification is achieved through concentration dependent homotypic assemblies of SHARP on the X and is required for chromosome-wide silencing. We find that expressing Xist at higher levels leads to increased localization at autosomal regions, demonstrating that low levels of Xist are critical for ensuring its specificity to the X chromosome. We show that Xist (through SHARP) acts to suppress production of its own RNA which may act to constrain overall RNA levels and restrict its ability to spread beyond the X. Together, our results demonstrate a spatial amplification mechanism that allows Xist to achieve two essential but countervailing regulatory objectives: chromosome-wide gene silencing and specificity to the X. Our results suggest that this spatial amplification mechanism may be a more general mechanism by which other low abundance lncRNAs can balance specificity to, and robust control of, their regulatory targets.

Determination of Sex Chromatin — A New Concept

1972 ◽  
Vol 21 (1-2) ◽  
pp. 149-170
Author(s):  
Syed Shane Raza Zaidi
Keyword(s):  
Sex Determination ◽  
Y Chromosome ◽  
X Chromosome ◽  
Mother Cell ◽  
Daughter Cell ◽  
Barr Body ◽  
X Chromosomes ◽  
Sex Chromatin

SummaryInstead of the random activation and/or inactivation of the X-chromosome in sex determination, as suggested by the Lyon's hypothesis, a proposal is made here that crossingover between the sister- and/or nonsisterstrands at the sticky or nonsticky loci, at heterochromatinizing regions and at the inactivating centers of the centromère, be responsible for the heterochromatinization and/or heteropyknotization of the X-chromosome. (This proposal will be called the Mustafa hypothesis.)Such would be the basis for the activation and/or inactivation of the X-chromatid(s), which would then replicate into a normal or a heterochromatic X-chromosome respectively. The heterochromatic X-chromosome may be transformed into a heteropyknotized mass of sex chromatin (Barr body). Translocation of the Y-chromosome and of some of the autosomes could also result in the same effect. Hence, the number of heterochromatinized X-chromosomes, and/or of heteropyknotized masses (Barr bodies), in each daughter-cell is directly proportional to half the number of chromatids involved in crossingover and/or translocation in the mother-cell.

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