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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.

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...

Chromosomal Theory of Inheritance

Chromosomal Theory of Inheritance

In 1866, Gregor Mendel published the results of his pea plant breeding experiments, providing evidence for predictable patterns in the inheritance of physical characteristics. The significance of his findings was not immediately recognized. In fact, the existence of genes was unknown at the time. Mendel referred to hereditary units as “factors.”

Genomic Imprinting and Inheritance

Genomic Imprinting and Inheritance

Diploid organisms inherit genetic material through chromosomes from both parents. Copies of the same gene are known as alleles. In most cases, both alleles are simultaneously expressed and allow various cellular processes to function optimally. If one of the alleles is missing or mutated, the expression of the other allele can compensate; however, this is not true for all genes.
The expression of some genes depends on which parent passed the gene to the offspring, through a phenomenon known as...

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Updated: May 30, 2026

Semiconductor Sequencing for Preimplantation Genetic Testing for Aneuploidy

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[Subfertility phenotype, chromosome polymorphism and conception failures].

Cássia de Lourdes Campanho¹, Juliana Karina Heinrich, Egle Couto

¹Centro de Atenção Integral à Saúde da Mulher, Universidade Estadual de Campinas, Campinas, SP, Brasil.

Revista Brasileira De Ginecologia E Obstetricia : Revista Da Federacao Brasileira Das Sociedades De Ginecologia E Obstetricia

|August 24, 2011

Summary

Cytogenetic alterations, including chromosomal abnormalities and polymorphic variants, were evaluated in Brazilian subfertile couples. No significant differences were found in prevalence related to reproductive loss history.

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Using Mouse Oocytes to Assess Human Gene Function During Meiosis I

Using Mouse Oocytes to Assess Human Gene Function During Meiosis I

Published on: April 10, 2018

Area of Science:

Human Genetics
Reproductive Medicine
Cytogenetics

Context:

Subfertility affects a significant portion of couples, with underlying genetic factors playing a crucial role.
Cytogenetic analysis, including karyotyping, is essential for diagnosing reproductive issues.
Understanding chromosomal variations in subfertile populations is vital for accurate genetic counseling.

Purpose:

To determine the prevalence of cytogenetic alterations and chromosomal polymorphic variants in Brazilian couples experiencing subfertility.
To investigate the association between these genetic variations and a history of reproductive losses.

Summary:

Karyotype analysis (G and C banding) was performed on 1,236 individuals from two Brazilian centers presenting with subfertility.
Approximately 25% of cases showed abnormal karyotypes, encompassing numerical and structural alterations, and polymorphic variants (prevalence 8.9% and 3.8% in the centers).
No statistically significant difference in the prevalence of polymorphic variants or other abnormalities was observed between individuals with or without a history of reproductive loss.

Impact:

Highlights the importance of comprehensive cytogenetic analysis in subfertile individuals.
Emphasizes the need for detailed reporting of all cytogenetic findings, particularly polymorphic variants, in karyotype reports.
Informs genetic counseling and diagnostic strategies for subfertile couples in Brazil and similar populations.