Question

Which of the following is represented by 2n - 2?
(a)Monosomic
(b)Trisomic
(c)Nullisomic
(d)Haploid

Answer 1

Hint : Aneuploidy is the state of the genome having a chromosome number that is not an accurate multiple of the haploid number of the organism.

Complete answer : In nullisomy, two homologous chromosomes are absent, and the chromosomal configuration is denoted by 2n - 2.

Additional information :
-Monosomy is a kind of aneuploidy with the appearance of only one chromosome from a pair. Partial monosomy happens when a part of one of the chromosomes in the pair is absent. It can be seen in Turner’s disease in which a female is born with only one X-chromosome.
-A trisomy is a type aneuploidy in which there are three copies of a particular chromosome, instead of the typical two. A trisomy is a type of polysomy (an abnormal number of chromosomes). It can be seen in Down syndrome in which there are three copies of chromosome 21 instead of two.
-Nullisomy is a genome modification where a pair of homologous chromosomes that would normally be there is absent. Therefore the chromosomal composition of nullisomy is denoted by 2n - 2. In plants, nullisomy can provide viable polyploid plants.
-Haploid is the terminology applied when a cell has half the usual number of chromosomes. A normal eukaryotic gamete organism is composed of diploid cells, one set of chromosomes from each parent. However, after meiosis, the number of chromosomes in gametes is halved, which is the haploid condition.

So, the correct answer is “nullisomic”.

Notes : Polysomy is a state found in many organisms, including fungi, plants, insects, and mammals, in which the organism has a minimum of one more chromosome than normal. In polysomy, there can be more than two copies of the chromosome.