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Related Concept Videos

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...
Meiosis I03:09

Meiosis I

Meiosis is the division of a diploid cell into haploid cells forming sperm and eggs in animals through differentiation. Meiosis I is the first stage of meiosis, where the genetic recombination of homologous chromosomes and the reduction of the ploidy level by half occurs.
Prophase I is the most extended and complex step of meiosis I characterized by synapsis, chromosome pairing, and recombination of the homologous chromosomes. This process is facilitated by a proteinaceous structure called the...
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.
Nondisjunction01:21

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.
Meiosis vs. Mitosis02:57

Meiosis vs. Mitosis

Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
Before the start of mitosis and meiosis I, the cell synthesizes DNA, resulting in two homologous copies of each chromosome. DNA synthesis is...

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Recurrence risks for trisomies 13, 18, and 21.

Elizabeth De Souza1, Jane Halliday, Annabelle Chan

  • 1Barts & The London School of Medicine and Dentistry, Queen Mary University of London, Wolfson Institute of Preventive Medicine, London, UK.

American Journal of Medical Genetics. Part A
|November 19, 2009
PubMed
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Women with a prior trisomy pregnancy face a higher risk of future trisomies, especially if under 35. This includes Patau syndrome (trisomy 13), Edwards syndrome (trisomy 18), and Down syndrome (trisomy 21).

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Area of Science:

  • Reproductive genetics
  • Maternal-fetal medicine
  • Birth defects epidemiology

Background:

  • Previous trisomic pregnancies (13, 18, 21) may alter recurrence risk.
  • Understanding recurrence risk is crucial for genetic counseling and reproductive planning.

Purpose of the Study:

  • To determine if a prior pregnancy with trisomy 13, 18, or 21 increases the risk of these trisomies in subsequent pregnancies.
  • To investigate the influence of maternal age at the time of the previous trisomic pregnancy on recurrence risk.

Main Methods:

  • Utilized data from three Australian population-based birth defect registers.
  • Analyzed 5,906 women with a previous trisomy pregnancy and their 3,713 subsequent pregnancies.
  • Calculated relative risk (RR) of subsequent trisomies by comparing observed to expected rates based on maternal age.

Main Results:

  • Increased risk for the same trisomy (13 or 18) after a previous affected pregnancy (RR=3.8), with higher risk for women under 35 (RR=7.8).
  • Increased risk for trisomy 21 after a previous trisomy 21 pregnancy (RR=2.2), also higher for women under 35 (RR=3.5).
  • A potential increased risk for a different trisomy following trisomy 21 was suggested (RR=1.4).

Conclusions:

  • Women with a history of trisomic pregnancy have an elevated risk of subsequent trisomic pregnancies.
  • This increased risk is particularly pronounced for women under 35 years old at the time of the previous affected pregnancy.
  • Findings support enhanced surveillance and genetic counseling for women with a history of trisomy.