Question

Nullisomic condition is represented by

• A. $2n-1$
• B. $2n+2$
• C. $2n-2$
• D. $2n+1$

Answer 1

Answer: (C)

Aneuploidy:
In aneuploidy, any change in the number of chromosomes in an organism would be different from the multiple of a basic set of chromosomes. It commonly arises due to non-disjunction of the two chromosomes of homologous pair so that one gamete comes to have an extra chromosome ( $n+1$ ) while the other is deficient in one chromosome ( $n-1$ ).

The fusion of these gametes ( $n-1$ or $n+1$ ) with normal gametes ( $n$ ) gives rise to different types of aneuploids. The non-disjunction of chromosomes can happen in either Anaphase-I or Anaphase-II.

Sr. No.	Gametic fusion	Types of aneuploidy	Result
1	$(n)+(n-1)$	$2n-1$ (monosomic condition)	Contains one chromosome less in a pair
2	$(n-1)+(n-1)$	$2n-2$ (nullisomic condition)	Lacks one entire set of chromosome
3	$(n)+(n+1)$	$2n+1$ (trisomic condition)	Contains one chromosome extra in a pair
4	$(n+1)+(n+1)$	$2n+2$ (tetrasomic condition)	Has one entire set of chromosome extra