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Introduction

  • Numerical chromosomal aberration:-Change in number of chromosomes.

E.g. Maize

Chromosome no.:-2n=20

Suppose, it becomes 2n=22( one chromosome added)

  • Normal condition in any organism is called diploid means chromosome always present in pair.
  • The number chromosomes increase or decrease and such kinds of abnormalities is called numerical chromosomal aberration.
  • It is also known as heteroploids.
  • Heteroploids are the individuals possessing the variant chromosome number.

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  • Heteroploids are grouped in to 2 categories:-

A.Aneuploidy

B.Euploidy

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Aneuploidy:

Aneuploidy is a genetic condition in which the number of chromosomes in a cell is not an exact multiple of the normal set.

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Types of Aneuploidy

1.Hyperploidy

2. Hypoploidy

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  1. Hyperploidy

Hyperploidy is a condition in which a cell or organism has more chromosomes than the normal diploid number (2n).

E.g.

  • Individual possessing one extra chromosome (2n+1) is called trisomic.
  • Double trisomic:-Two nonhomologous chromosomes (each chromosome from a different pair ) extra (2n+1+1).
  • Tetrasomic:-One chromosome pair extra (2n+2).

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2. Hypoploidy

Hypoploidy is a type of aneuploidy in which a cell has fewer chromosomes than the normal diploid number for that species.

E.g.

  • Nullisomic:-One chromosome pair missing (2n-2).
  • Monosomic:-One chromosome missing (2n-1).
  • Double monosomic:-Two nonhomologous chromosomes (each chromosome from different pair ) missing (2n-1-1).

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Euploidy

The addition of one or more complete sets of chromosomes to the original set is called euploidy.Euploidy is of two types:-

a.Monoploid

b.Polyploid

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Types of Polyploid

A.Autopolyploid

B.Allopolyploid

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A.Autopolyploid

  • Autopolyploid refers to an organism that has more than two sets of chromosomes, and all the chromosome sets come from the same species..
  • E.g

Autotriploid: three copies of the same genome present (3x).

Autotetraploid:Four copies of the same genome present (4x).

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B.Allopolyploid

  • Allopolyploid refers to an organism that has more than two sets of chromosomes, but the chromosome sets come from different species.
  • E.g

Allotetraploid:Two distinct genomes; each has two copies.

Alohexaploid: Three distinct genomes; each has two copies.

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