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The majority of cases result from nondisjunction during maternal meiosis I. [14] Trisomy occurs in at least 0.3% of newborns and in nearly 25% of spontaneous abortions. It is the leading cause of pregnancy wastage and is the most common known cause of intellectual disability. [15]
This is an accepted version of this page This is the latest accepted revision, reviewed on 16 February 2025. Cell division producing haploid gametes For the figure of speech, see Meiosis (figure of speech). For the process whereby cell nuclei divide to produce two copies of themselves, see Mitosis. For excessive constriction of the pupils, see Miosis. For the parasitic infestation, see Myiasis ...
Numerical abnormalities, also known as aneuploidy, often occur as a result of nondisjunction during meiosis in the formation of a gamete; trisomies, in which three copies of a chromosome are present instead of the usual two, are common numerical abnormalities.
The extra chromosome is retained because of a nondisjunction event during paternal meiosis I, maternal meiosis I, or maternal meiosis II, also known as gametogenesis. The relevant nondisjunction in meiosis I occurs when homologous chromosomes, in this case the X and Y or two X sex chromosomes, fail to separate, producing a sperm with an X and a ...
47,XYY is not inherited; it usually occurs as a random event during the formation of sperm cells. An incident in chromosome separation during anaphase II (of meiosis II) called nondisjunction can result in sperm cells with an extra copy of the Y-chromosome. If one of these atypical sperm cells contributes to the genetic makeup of a child, the ...
Polyploidy, or whole genome duplication is a product of nondisjunction during meiosis which results in additional copies of the entire genome. Polyploidy is common in plants, but it has also occurred in animals, with two rounds of whole genome duplication ( 2R event ) in the vertebrate lineage leading to humans. [ 4 ]
This process results in each gamete usually containing a mixture of chromosomes from both original parents. Improper chromosome segregation (see non-disjunction, disomy) can result in aneuploid gametes having either too few or too many chromosomes. The second stage at which segregation occurs during meiosis is prophase II (see meiosis diagram ...
Non-random segregation of chromosomes is a deviation from the usual distribution of chromosomes during meiosis, that is, during segregation of the genome among gametes.While usually according to the 2nd Mendelian rule (“Law of Segregation of genes“) homologous chromosomes are randomly distributed among daughter nuclei, there are various modes deviating from this in numerous organisms that ...