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Nondisjunction

Nondisjunction

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.

Nondisjunction

Nondisjunction

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 sister...

Nondisjunction

Nondisjunction

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.

The Ratio of X Chromosome to Autosomes

The Ratio of X Chromosome to Autosomes

In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...

Meiosis vs. Mitosis

Meiosis vs. Mitosis

Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
Before the start of mitosis and meiosis I, the cell synthesizes DNA, resulting in two homologous copies of each chromosome. DNA synthesis is...

Sex Linked Disorders

Sex Linked Disorders

Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological deficits, the disorder is considered sex-linked.

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Autosomal and X chromosome structural variants are associated with congenital heart defects in Turner syndrome: The NHLBI GenTAC registry.

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The relation between X chromosome parental origin and aortic stiffness in patients with Turner's syndrome: role of hypertension and antihypertensive drugs.

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Related Experiment Video

Updated: Jun 26, 2026

Generation of Induced Pluripotent Stem Cells from Turner Syndrome (45XO) Fetal Cells for Downstream Modelling of Neurological Deficits Associated with the Syndrome

Generation of Induced Pluripotent Stem Cells from Turner Syndrome (45XO) Fetal Cells for Downstream Modelling of Neurological Deficits Associated with the Syndrome

Published on: December 4, 2021

Turner syndrome 2008.

Carolyn A Bondy¹

¹Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA. bondyc@mail.nih.gov

Hormone Research

|January 21, 2009

Summary

This summary is machine-generated.

Turner syndrome (TS) management has evolved. Early diagnosis and tailored treatments, including growth and puberty induction, improve outcomes for girls with TS, while cardiac screening is vital for adult survival.

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Generation of Induced Pluripotent Stem Cells from Turner Syndrome (45XO) Fetal Cells for Downstream Modelling of Neurological Deficits Associated with the Syndrome

Generation of Induced Pluripotent Stem Cells from Turner Syndrome (45XO) Fetal Cells for Downstream Modelling of Neurological Deficits Associated with the Syndrome

Published on: December 4, 2021

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FISH for Pre-implantation Genetic Diagnosis

FISH for Pre-implantation Genetic Diagnosis

Published on: February 23, 2011

Area of Science:

Genetics and Developmental Biology
Pediatric Endocrinology
Reproductive Medicine

Background:

Prenatal diagnosis of 45,X Turner syndrome (TS) with abnormal ultrasounds indicates a poor prognosis, but survival with modern management leads to good outcomes.
Incidental diagnoses of 45,X mosaicism in fetuses with normal ultrasounds show high survival rates and potentially mild or no TS features.

Purpose of the Study:

To outline current management strategies for Turner syndrome.
To emphasize optimizing adult height and psychosocial adjustment in girls with TS.
To highlight the importance of screening for premature mortality risks in adults with TS.

Main Methods:

Review of current medical management and treatment recommendations for Turner syndrome.
Discussion of growth-promoting therapies and pubertal induction protocols.
Emphasis on psychosocial support for ovarian failure and cardiac screening protocols.

Main Results:

Modern medical management can lead to good clinical outcomes for surviving fetuses with 45,X TS.
Microdose estradiol is recommended for initiating puberty to mimic normal physiology.
There is a high rate of premature mortality in adults with TS due to congenital heart disease complications.

Conclusions:

Optimizing adult height and psychosocial adjustment are key goals in TS management.
Cardiac magnetic resonance imaging is crucial for screening high-risk individuals with TS.
Addressing premature mortality through vigilant cardiac screening is essential for improving long-term survival in Turner syndrome patients.