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Related Concept Videos

X-Inactivation01:58

X-Inactivation

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The human X chromosome contains over ten times the number of genes as in the Y chromosome. Since males have only one X chromosome, and females have two, one might expect females to produce twice as many of the proteins, with undesirable results.
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Inheritance of Chromatin Structures03:17

Inheritance of Chromatin Structures

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Epigenetics is the study of inherited changes in a cell's phenotype without changing the DNA sequences. It provides a form of memory for the differential gene expression pattern to maintain cell lineage, position-effect variegation, dosage compensation, and maintenance of chromatin structures such as telomeres and centromeres. For example, the structure and location of the centromere on chromosomes are epigenetically inherited. Its functionality is not dictated or ensured by the underlying...
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Nondisjunction01:21

Nondisjunction

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Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This produces daughter cells with abnormal chromosome numbers.  Nondisjunction is common during anaphase I or anaphase II of meiosis.  Mutations in synaptonemal complex proteins that attach homologous chromosomes increase the chances of nondisjunction in anaphase I of meiosis I. In contrast, mutations in topoisomerases and condensins that hold...
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Nondisjunction01:29

Nondisjunction

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During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.
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Dosage Compensation02:50

Dosage Compensation

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In animals, gender is determined by the number and type of sex chromosome. For example, human females have two X chromosomes, and males have one X and one Y chromosome, whereas C.elegans with one X chromosome is a male, and the one with two X chromosomes is a hermaphrodite.
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Related Experiment Video

Updated: Mar 23, 2026

Chromosome Screening of Human Preimplantation Embryos by Using Spent Culture Medium: Sample Collection and Chromosomal Ploidy Analysis
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[SKEWED X-CHROMOSOME INACTIVATION IN HUMAN MISCARRIAGES].

E N Tolmacheva, S A Vasilyev, E A Sazhenova

    Tsitologiia
    |March 26, 2016
    PubMed
    Summary

    Female embryo loss in early pregnancy may stem from abnormal X-chromosome inactivation. Skewed inactivation in extraembryonic tissues was linked to miscarriages, particularly in blighted ovum and recurrent pregnancy loss cases.

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    Combined DNA-RNA Fluorescent In situ Hybridization FISH to Study X Chromosome Inactivation in Differentiated Female Mouse Embryonic Stem Cells
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    Area of Science:

    • Reproductive Biology
    • Genetics
    • Developmental Biology

    Context:

    • The sex ratio at conception often deviates from 1:1, with a higher incidence of male births.
    • Preferential elimination of female embryos in the first trimester is a proposed cause for this skewed sex ratio.
    • Aberrant X-chromosome inactivation in female embryos is hypothesized to contribute to this phenomenon.

    Purpose:

    • To investigate X-chromosome inactivation patterns in extraembryonic tissues of early pregnancy losses (miscarriages and induced abortions) with a 46,XX karyotype.
    • To compare X-chromosome inactivation in chorion cytotrophoblast and extraembryonic mesoderm between control and pregnancy loss groups.

    Summary:

    • X-chromosome inactivation analysis was performed on extraembryonic tissues from miscarriages and induced abortions (46,XX).
    • Both random and skewed X-chromosome inactivation were observed in the chorion cytotrophoblast of all studied groups.
    • While the control group showed random inactivation in extraembryonic mesoderm, 15% of miscarriages exhibited skewed inactivation.
    • The highest frequency of skewed inactivation was found in blighted ovum pregnancies and embryos from women with recurrent pregnancy loss.

    Impact:

    • These findings suggest that skewed X-chromosome inactivation in extraembryonic tissues may play a role in early pregnancy failure.
    • The study proposes that blastocyst compartmentalization could lead to the dominance of cells with mutant active X-chromosomes, causing developmental incompatibilities.
    • Understanding these mechanisms could inform future research into the causes of recurrent pregnancy loss and improve reproductive outcomes.