Meiotic nondisjunction

Failure of two members of a chromosome pair to separate (disjoin) during meiosis so that both go to one daughter cell and none to the other. This mechanism is responsible for the extra chromosome 21 in trisomy 21 (Down syndrome) and for extra and missing chromosomes causing other birth defects and many spontaneous abortions (miscarriages).

Medical dictionary. 2011.

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  • Nondisjunction — Failure of paired chromosomes to disjoin (separate) during cell division so that both chromosomes go to one daughter cell and none to the other. Nondisjunction causes errors in chromosome number such as trisomy 21 (Down s syndrome) and monosomy X …   Medical dictionary

  • Genetic origins of Down syndrome — Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on the 21st chromosome, either in whole (trisomy 21) or part (such as due to translocations). The effects of the extra copy varies… …   Wikipedia

  • Down syndrome — Classification and external resources Boy with Down syndrome assembling a …   Wikipedia

  • genetic disease, human — Introduction       any of the diseases and disorders that are caused by mutations in one or more genes (gene).       With the increasing ability to control infectious and nutritional diseases in developed countries, there has come the realization …   Universalium

  • Edwards syndrome — Infobox Disease Name = Trisomy 18 Caption = Chromosome 18 DiseasesDB = 13378 ICD10 = ICD10|Q|91|0|q|90 ICD10|Q|91|3|q|90 ICD9 = ICD9|758.2 ICDO = OMIM = MedlinePlus = eMedicineSubj = ped eMedicineTopic = 652 MeshID = Trisomy 18 or Edwards… …   Wikipedia

  • Meiosis — Not to be confused with miosis, mitosis, or myositis. For the figure of speech, see meiosis (figure of speech). Events involving meiosis, showing chromosomal crossover Meiosis (pronounced /maɪˈoʊsɨs/&# …   Wikipedia

  • Homologous recombination — Figure 1. During meiosis, homologous recombination can produce new combinations of genes as shown here between similar but not identical copies of human chromosome 1. Homologous recombination is a type of genetic recombination in which nucleotide …   Wikipedia

  • heredity — /heuh red i tee/, n., pl. heredities. Biol. 1. the transmission of genetic characters from parents to offspring: it is dependent upon the segregation and recombination of genes during meiosis and fertilization and results in the genesis of a new… …   Universalium

  • reduction division — noun (genetics) cell division that produces reproductive cells in sexually reproducing organisms; the nucleus divides into four nuclei each containing half the chromosome number (leading to gametes in animals and spores in plants) • Syn: ↑meiosis …   Useful english dictionary

  • Y chromosome — Human Y chromatid The Y chromosome is one of the two sex determining chromosomes in most mammals, including humans. In mammals, it contains the gene SRY, which triggers testis development if present. The human Y chromosome is composed of about 60 …   Wikipedia

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