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Meiosis I

Meiosis I

Meiosis is a carefully orchestrated set of cell divisions, the goal of which—in humans—is to produce haploid sperm or eggs, each containing half the number of chromosomes present in somatic cells elsewhere in the body. Meiosis I is the first such division, and involves several key steps, among them: condensation of replicated chromosomes in diploid cells; the pairing of homologous chromosomes and their exchange of information; and finally, the separation of homologous chromosomes by a...

Gene Duplication and Divergence

Gene Duplication and Divergence

The seminal work of Ohno in 1970 popularized the idea of gene duplication and divergence. DNA sequence comparison studies reveal that a large portion of the genes in bacteria, archaebacteria, and eukaryotes was generated by gene duplication and divergence, indicating its critical role in evolution.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are characterized.

Chromosome Duplication

Chromosome Duplication

The process of chromosome duplication during cell division requires genome-wide disruption and re-assembly of chromatin. The chromatin structure must be accurately inherited, reassembled, and maintained in the daughter cells to ensure lineage propagation.
The basic unit of the chromatin is the nucleosome, consisting of DNA wrapped around octameric histone proteins and short stretches of linker DNA separating individual nucleosomes. The histone proteins within the nucleosome have their...

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.

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Related Experiment Video

Updated: May 11, 2026

Midface Hypoplasia and Cranial Base Morphology in Syndromic Craniosynostosis: A Comparative Analysis Study Using a Predictive Regression Model

Midface Hypoplasia and Cranial Base Morphology in Syndromic Craniosynostosis: A Comparative Analysis Study Using a Predictive Regression Model

Published on: November 4, 2025

Partial midfacial duplication.

Weimin Shen¹, Jie Cui, Jianbin Chen

¹Department of Plastic Surgery, Nanjing Children's Hospital affiliated Nanjing Medical University, Nanjing, China. shenweiminchina@hotmail.com

The Journal of Craniofacial Surgery

|May 30, 2013

Summary

This case study details the surgical management of craniofacial duplication, a rare congenital anomaly. Early intervention and comprehensive surgical planning are crucial for optimal outcomes in affected infants.

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Midface Hypoplasia and Cranial Base Morphology in Syndromic Craniosynostosis: A Comparative Analysis Study Using a Predictive Regression Model

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Area of Science:

Craniofacial Surgery
Pediatric Neurosurgery
Congenital Malformations

Background:

Craniofacial duplication is an extremely rare congenital anomaly characterized by duplication of facial structures.
This condition presents complex challenges in diagnosis and surgical management, often requiring multidisciplinary care.
Literature review highlights the rarity and varied presentations of craniofacial duplication, emphasizing the need for tailored treatment strategies.

Observation:

A neonate presented with craniofacial duplication, including a duplicated maxilla and bilateral macrostomia.
Recurrent masses at the skull base, identified via CT scan, were associated with a cranial meningocele and malformation of the first cervical vertebra.
The patient developed a palate fistula post-operatively, necessitating further surgical repair.

Findings:

Surgical excision of the duplicated maxilla and subsequent management of a recurrent cranial meningocele were performed.
Repair of a palate cleft and closure of the cerebral meningocele were critical components of the treatment.
Delayed repair of the palate fistula and macrostomia were addressed in subsequent procedures.

Implications:

This case underscores the importance of immediate surgical intervention for craniofacial duplication to address life-threatening issues like dyspnea.
A well-planned, staged surgical approach is essential for correcting complex craniofacial deformities and associated anomalies.
Optimal timing and comprehensive surgical planning can significantly improve the functional and aesthetic outcomes for patients with craniofacial duplication.