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Related Concept Videos

Nondisjunction01:21

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...
Nondisjunction01:29

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.
Nondisjunction01:29

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.
Genomic Imprinting and Inheritance02:30

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...
Neurulation01:30

Neurulation

Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three primary cell layers of the embryo: ectoderm, mesoderm, and endoderm. In humans, the majority of this system is formed via primary neurulation, in which the central portion of the ectoderm—originally appearing as a flat sheet of cells—folds upwards and inwards, sealing off to form a hollow neural tube. As development proceeds, the anterior...
Meiosis I01:49

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...

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Related Experiment Video

Updated: May 29, 2026

Development of a Neonatal Rat Model for Brachial Plexus Birth Injury
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Sirenomelia.

Gouranga Santra, Narayan Pandit, Pradip K Sinha

    The New Zealand Medical Journal
    |September 29, 2011
    PubMed
    Summary

    Sirenomelia, a rare congenital fusion of the legs, can present with unusual upper body defects. This case highlights rare malformations of the forearm, hand, and rib cage in sirenomelia.

    Area of Science:

    • Embryology
    • Developmental Biology
    • Teratology

    Background:

    • Sirenomelia (mermaid syndrome) is a rare congenital malformation characterized by fusion of the lower limbs.
    • It is associated with significant internal anomalies, particularly renal, intestinal, and genital abnormalities.
    • A single umbilical artery is a common finding in sirenomelia.

    Observation:

    • This report details a rare case of sirenomelia presenting with uncommon upper body malformations.
    • Observed defects included anomalies of the right forearm and hand, and the rib cage.
    • These upper body defects were not attributable to a vascular steal phenomenon.

    Findings:

    • The case demonstrates that sirenomelia can manifest with complex and atypical upper body congenital anomalies.

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  • The etiology of these upper body defects in the context of sirenomelia remains unclear and warrants further investigation.
  • Standard explanations like vascular steal phenomenon do not adequately account for the observed upper body malformations.

    • Implications:

    • This case expands the known spectrum of sirenomelia presentations.
    • It underscores the need for comprehensive evaluation of all fetal body parts in cases of sirenomelia.
    • Further research is needed to understand the developmental mechanisms behind these rare upper body defects.