Q. Nullisomic condition is represented by
NTA AbhyasNTA Abhyas 2020
Solution:
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 $\left(\right.n\left.\right)+\left(\right.n-1\left.\right)$ $2n-1$ (monosomic condition) Contains one chromosome less in a pair 2 $\left(\right.n-1\left.\right)+\left(\right.n-1\left.\right)$ $2n-2$ (nullisomic condition) Lacks one entire set of chromosome 3 $\left(\right.n\left.\right)+\left(\right.n+1\left.\right)$ $2n+1$ (trisomic condition) Contains one chromosome extra in a pair 4 $\left(\right.n+1\left.\right)+\left(\right.n+1\left.\right)$ $2n+2$ (tetrasomic condition) Has one entire set of chromosome extra
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 ( $n-1$ ).
| Sr. No. | Gametic fusion | Types of aneuploidy | Result |
| 1 | $\left(\right.n\left.\right)+\left(\right.n-1\left.\right)$ | $2n-1$ (monosomic condition) | Contains one chromosome less in a pair |
| 2 | $\left(\right.n-1\left.\right)+\left(\right.n-1\left.\right)$ | $2n-2$ (nullisomic condition) | Lacks one entire set of chromosome |
| 3 | $\left(\right.n\left.\right)+\left(\right.n+1\left.\right)$ | $2n+1$ (trisomic condition) | Contains one chromosome extra in a pair |
| 4 | $\left(\right.n+1\left.\right)+\left(\right.n+1\left.\right)$ | $2n+2$ (tetrasomic condition) | Has one entire set of chromosome extra |