Question

Aneuploidy is characterized by

• A. presence of three sets of chromosomes
• B. presence of an extra copy of chromosome
• C. absence of a copy of chromosome
• D. both b and c

Answer 1

The correct option is D both b and c

The loss or addition of one or few chromosomes leading to an unbalanced chromosome complement is called aneuploidy.

Failure of separation of homologous pairs of chromosomes during meiosis I or failure of separation of sister chromatids during meiosis II is called nondisjunction and this leads to aneuploidy.

Aneuploidy is of two types: hypoploidy and hyperploidy.

Hypoploidy is characterised by the lack of one or few chromosomes.

Monosomy and nullisomy are types of hypoploidy.

In monosomy, there is lack of a single chromosome and in nullisomy there is lack of two chromosomes.

In human beings, monosomy is represented as 2n-1 and nullisomy is represented as 2n-2.
2n refers to the diploid set of chromosomes.

Hyperploidy is characterised by the presence of extra copies of one or few chromosomes.

Trisomy and tetrasomy are types of hyperploidy.

In trisomy, there are three copies of a particular chromosome in a cell.

In tetrasomy, there are four copies of a particular chromosome.

In human beings, trisomy is represented as 2n+1 and tetrasomy is represented as 2n+2.

Presence of three sets of chromosomes in a cell is called triploidy (a type of polyploidy) which mostly results due to failure of cytokinesis.