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      • A trisomy is a type of polysomy in which there are three instances of a particular chromosome, instead of the normal two. A trisomy is a type of aneuploidy (an abnormal number of chromosomes).


      Description and causes


      Most organisms that reproduce sexually have pairs of chromosomes in each cell, with one of each type of chromosome inherited from each parent. In such organisms, meiosis creates gamete cells (eggs or sperm) having only one set of chromosomes. The number of chromosomes is different for different species, with humans having 46 chromosomes (23 pairs) and human gametes 23 chromosomes.
      If the chromosome pairs fail to separate properly during cell division, the egg or sperm may end up with a second copy of one of the chromosomes (non-disjunction). If such a gamete is fertilized with a normal gamete, the resulting embryo may have a total of three copies of the chromosome.


      = Terminology

      =
      The number of chromosomes in the cell where trisomy occurs is represented as, for example, 2n+1 if one chromosome shows trisomy, 2n+1+1 if two show trisomy, etc.

      "Full trisomy", also called "primary trisomy", means that an entire extra chromosome has been copied.
      "Partial trisomy" means that there is an extra copy of part of a chromosome.
      "Secondary trisomy" - the extra chromosome has quadruplicated arms (the arms are identical; it is an "isochromosome").
      "Tertiary trisomy" - the extra chromosome is made up of copies of arms from two other chromosomes.
      Trisomies are sometimes characterised as "autosomal trisomies" (trisomies of the non-sex chromosomes) and "sex-chromosome trisomies." Autosomal trisomies are described by referencing the specific chromosome that has an extra copy. Thus, for example, the presence of an extra chromosome 21, which is found in Down syndrome, is called trisomy 21.


      Human trisomy



      Trisomies can occur with any chromosome, but often result in miscarriage rather than live birth. For example, Trisomy 16 is most common in human pregnancies, occurring in more than 1%, but the only surviving embryos are those having some normal cells in addition to the trisomic cells (mosaic trisomy 16). Furthermore, even these embryos usually suffer spontaneous miscarriage in the first trimester.
      The most common types of human autosomal (non-sex chromosome) trisomy that survive to birth are:

      Trisomy 21 (Down syndrome)
      Trisomy 18 (Edwards syndrome)
      Trisomy 13 (Patau syndrome)
      Trisomy 9
      Trisomy 8 (Warkany syndrome 2)
      Of these, Trisomy 21 and Trisomy 18 are the most common. In rare cases, a fetus with Trisomy 13 can survive, giving rise to Patau syndrome. Autosomal trisomy can be associated with birth defects, intellectual disability and shortened life.
      Trisomy of sex chromosomes can also occur and include:

      XXX (Triple X syndrome)
      XXY (Klinefelter syndrome)
      XYY (Jacobs syndrome)
      Compared to trisomy of the autosomal chromosomes, trisomy of the sex chromosomes normally has less severe consequences. Individuals may show few or no symptoms and have a normal life expectancy.


      See also


      Chromosome abnormalities
      Aneuploidy
      Karyotype
      Sexual reproduction
      Monosomy


      References

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    Artikel Terkait "trisomy"

    Trisomy: Types of Trisomy Disorders - Cleveland Clinic

    03 Mei 2022 · Trisomy is a genetic condition that results in an extra copy of a chromosome. A person with trisomy will have 47 chromosomes instead of 46. Trisomy pregnancies can result …

    Trisomy - Wikipedia

    A trisomy is a type of polysomy in which there are three instances of a particular chromosome, instead of the normal two. [1] A trisomy is a type of aneuploidy (an abnormal number of chromosomes).

    Types of Trisomy: Causes and Symptoms - Verywell Health

    21 Jan 2024 · A trisomy is a genetic disorder in which a person has three chromosomes instead of the usual two. The most well-known trisomy is Down syndrome, but there are others like …

    Trisomy 18 (Edwards Syndrome): Symptoms, Causes, Diagnosis - WebMD

    28 Feb 2024 · Trisomy 18 is a condition where you have three copies of each chromosome 18 in your body's cells instead of two. This can lead to serious physical and mental disabilities.

    Trisomy 13 (Patau Syndrome) - Cleveland Clinic

    Trisomy 13 (Patau syndrome) is a rare genetic condition that occurs when the 13th chromosome appears three times (trisomy) instead of two times in a person’s DNA. Trisomy 13 affects the development of the face, brain and heart, along with physical …

    Trisomies and Monosomies - Boston Children's Hospital

    A trisomy and a monosomy are types of numerical chromosome abnormalities that can cause certain birth defects. Normally, people are born with 23 chromosome pairs, or 46 chromosomes, in each cell — one inherited from the mother and one from the father.

    Trisomy | Description, Cause, & Examples | Britannica

    Trisomy, abnormality in chromosome number (aneuploidy), characterized by the existence of an extra chromosome, resulting in three copies of the affected chromosome, rather than the typical two copies. As a result, individuals with a trisomy disorder carry …

    Trisomy 21 (Down Syndrome) - Children's Hospital of Philadelphia

    Trisomy 21 is the most common chromosomal anomaly in humans, affecting about 5,000 babies born each year and more than 350,000 people in the United States. Also known as Down syndrome, trisomy 21 is a genetic condition caused by an extra chromosome.

    Numerical Abnormalities: Overview of Trisomies and Monosomies

    The term "trisomy" is used to describe the presence of three chromosomes, rather than the usual pair of chromosomes. For example, if your baby is born with three #21 chromosomes, rather than the usual pair, your baby would be said to have "trisomy …

    What Are Chromosomal Trisomies? - iCliniq

    16 Mar 2023 · Trisomy occurs when a person has three copies of a chromosome rather than two. The consequences of chromosomal trisomy differ depending on the pair of chromosomes involved and the magnitude of the imbalance induced by the additional chromosome.