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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.

Pleiotropy

Pleiotropy

Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene cause Waardenburg Syndrome Type 4, or WS4, which can cause defects in pigmentation, hearing impairments, and an absence of intestinal contractions necessary for elimination. This diversity of phenotypes results from the expression pattern of SOX10 in early embryonic and fetal development. SOX10 is found in neural crest cells that form melanocytes,...

Multiple Allele Traits

Multiple Allele Traits

The Concept of Multiple Allelism

Epistasis

Epistasis

In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence phenotypes in a phenomenon called epistasis. For example, rabbit fur can be black or brown depending on whether the animal is homozygous dominant or heterozygous at a TYRP1 locus. However, if the rabbit is also homozygous recessive at a locus on the tyrosinase gene (TYR), it will have an unshaded coat that appears white, regardless of its TYRP1...

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Related Experiment Video

Updated: May 25, 2026

Model Surgical Training: Skills Acquisition in Fetoscopic Laser Photocoagulation of Monochorionic Diamniotic Twin Placenta Using Realistic Simulators

Model Surgical Training: Skills Acquisition in Fetoscopic Laser Photocoagulation of Monochorionic Diamniotic Twin Placenta Using Realistic Simulators

Published on: March 21, 2018

Heteropagus twinning on back -- a case report.

Bidyut Debnath¹, Sumitra Kumar Biswas

¹Dr BC Roy Memorial Hospital for Children, Kolkata 700054.

Journal of the Indian Medical Association

|February 10, 2012

Summary

This study reports a rare case of heteropagus twins, a parasitic twin malformation. The parasite had a well-formed limb and intestine, attached to the host twin by a pedicle.

Area of Science:

Medical Science
Developmental Biology
Teratology

Background:

Heteropagus twins, a rare congenital malformation, involve an incompletely developed twin attached to a host twin.
Parasitic twins most commonly attach to the host's torso, typically the chest or abdomen.
Distinguishing heteropagus twins from other conditions like fetus in fetu and teratomas can be challenging.

Observation:

A case of heteropagus twin is presented, characterized by a parasitic twin with distinct anatomical features.
The parasitic twin exhibited a well-formed limb and a blind-ending intestinal tract.
Attachment to the host twin occurred via a broad pedicle, originating from the host's back.

Findings:

The presented case highlights the variable morphology and attachment sites of heteropagus twins.

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Guide Wire Assisted Catheterization and Colored Dye Injection for Vascular Mapping of Monochorionic Twin Placentas

Published on: September 5, 2011

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Last Updated: May 25, 2026

Model Surgical Training: Skills Acquisition in Fetoscopic Laser Photocoagulation of Monochorionic Diamniotic Twin Placenta Using Realistic Simulators

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Published on: March 21, 2018

Guide Wire Assisted Catheterization and Colored Dye Injection for Vascular Mapping of Monochorionic Twin Placentas

Guide Wire Assisted Catheterization and Colored Dye Injection for Vascular Mapping of Monochorionic Twin Placentas

Published on: September 5, 2011

The presence of developed structures in the parasite, such as a limb and intestine, underscores the complexity of this malformation.

This case contributes to the understanding of parasitic twin development and its anatomical variations.

Implications:

Clarifying the classification of twinning anomalies, including heteropagus twins, fetus in fetu, teratomas, and caudal duplications, is crucial for accurate diagnosis and management.
Further research into the developmental pathways of parasitic twinning can improve prenatal diagnosis and counseling.
Understanding these rare conditions aids in differentiating them from other congenital abnormalities, improving patient care.