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In Genetics, what is Nondisjunction?

Nondisjunction is a genetic mishap where chromosomes fail to separate properly during cell division, leading to cells with abnormal chromosome numbers. This can result in disorders like Down syndrome. Understanding nondisjunction is crucial for grasping how chromosomal abnormalities occur. How might this knowledge impact future genetic research? Continue reading to uncover the implications.
Larry Ray Palmer
Larry Ray Palmer

In the field of genetics, "nondisjunction" is a technical term for a specific defect in the way the chromosomes of a cell separate. This defect creates a genetic mutation or defect in the cells produced from the process. The resulting cells are called aneuploid. There are two crucial stages of cellular division when this defect can occur. The first stage is meiosis I, when the homologous chromosomes fail to separate, while the second is meiosis II, commonly known as mitosis, when the sister chromatids do not separate properly.

When nondisjunction occurs during meiosis I, all of the resulting gametes, called daughter cells, are affected. Two of the daughter cells will have an extra chromosome, and the other two daughter cells will be missing one chromosome.

Only half of the resulting daughter cells will be affected when this defect occurs during meiosis II. Of the four resulting gametes, two will be normal, one will have an extra chromosome, and one will be missing a chromosome.

Nondisjunction is a term for a specific defect in the way the chromosomes of a cell separate.
Nondisjunction is a term for a specific defect in the way the chromosomes of a cell separate.

When carried through in genetics, nondisjunction can result in either the sperm or the egg cells of the parent possessing 24 chromosomes instead of the normal 23. In these cases, the child conceived will have 47 chromosomes, which is the common variation known as trisomy, seen in children with Down syndrome.

When cells are missing a single chromosome, it is called monosomy. This form of genetic mutation can lead to birth defects such as Turner syndrome, a syndrome marked by developmental delays. It also can lead to infertility caused by the lack of genetic material.

Nondisjunction can lead to genetic defects like Down's Syndrome.
Nondisjunction can lead to genetic defects like Down's Syndrome.

Genetically, nondisjunction is often a death sentence for the fetus. As a result of the abnormal cellular structure, the immune system of the mother will often kick in, destroying the rogue cells and causing a miscarriage. In other cases, it leads to genetic defects, referred to as chromosomal anomalies, that result in conditions such as Down syndrome, Edwards syndrome, Patau syndrome, Klinefelter syndrome, and Turner syndrome.

Nondisjunction creates a genetic defect.
Nondisjunction creates a genetic defect.

While genetic testing, including antenatal testing, is used to detect genetic disorders, there are no known cures for many of the conditions caused by this defect. Medical science continues to study this mutation process in hopes of understanding why the cells fail to replicate properly. Mapping out the variations found in the cells produced by this condition may help researchers to find cures for genetic diseases and defects.

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Discussion Comments

werterful

Polyploidy is when an organism has extra sets of chromosomes. This occurs most often in plants. When it occurs in mammals it is deadly, but grapes and bananas are polyploids and they do just fine. An organism with three sets of chromosomes is called a triploid. An organism with four sets of chromosomes is called a tetraploid.

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    • Nondisjunction is a term for a specific defect in the way the chromosomes of a cell separate.
      By: He2
      Nondisjunction is a term for a specific defect in the way the chromosomes of a cell separate.
    • Nondisjunction can lead to genetic defects like Down's Syndrome.
      By: gregorydean
      Nondisjunction can lead to genetic defects like Down's Syndrome.
    • Nondisjunction creates a genetic defect.
      By: eabff
      Nondisjunction creates a genetic defect.
    • Down syndrome is considered a genetic nondisjunction.
      By: karelnoppe
      Down syndrome is considered a genetic nondisjunction.