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Q.Draw diagram of different types of aneuploidy.

Tamil Nadu DgeTamil Nadu HSC (DGE) Board 2023Subjective· 3mImportance★★★★★
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Figure — A comparative diagram showing a normal diploid set (e.g. two homologous pairs drawn as rod-shaped ch
Figure — A comparative diagram showing a normal diploid set (e.g. two homologous pairs drawn as rod-shaped ch

Aneuploidy involves loss or gain of individual chromosomes and includes monosomy, nullisomy, trisomy, tetrasomy, and double trisomy.

Aneuploidy is a chromosomal aberration in which the chromosome number deviates from the normal diploid (2n) complement by the loss or gain of one or a few individual chromosomes, rather than by the loss or gain of a whole haploid set (which is instead called euploidy/polyploidy). Aneuploidy typically arises from non-disjunction -- the failure of homologous chromosomes or sister chromatids to separate properly during meiosis or mitosis.

The main types of aneuploidy, illustrated diagrammatically as chromosome-count changes relative to a normal diploid set, are:

  1. Monosomy (2n-1): one chromosome of a particular homologous pair is missing, so that pair is represented by only a single chromosome.
  2. Nullisomy (2n-2): both members of a particular homologous pair are missing, so that chromosome type is entirely absent.
  3. Trisomy (2n+1): one extra chromosome of a particular type is present, so that type is represented by three chromosomes instead of two (e.g., Down syndrome in humans is a trisomy).
  4. Tetrasomy (2n+2): two extra copies of one chromosome type are present, giving four chromosomes of that type instead of two. …

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