Question

How many chromosomes are in a cell?

Answer 1

The number of chromosomes in a cell differs from species to species. In the case of humans, there are $23$ pairs (a total of $46$ chromosomes). In the case of the rice plant, there are $12$ pairs of chromosomes and $4$ pairs for a fruit fly. The plant Haplopappus gracilis has the lowest number of chromosomes ($2n = 4$) and fern Ophioglossum reticulatum has the highest number of chromosomes ($1260$).

Complete answer:
Chromosomes can be defined as rod-shaped or filamentous, gene bearing, self duplicating nuclear components which bear the hereditary information and are present in a definite number and are passed from the mother to daughter cells during the process of reproduction. The difference in the chromosome number can occur due to various reasons one of which is fusion (two chromosomes are stuck together during the cell division) due to which there is a decrease in the chromosome number. The other factor that causes a change in the chromosome number is polyploidy (it is an inherited condition in which there are more than two sets of a chromosome) causing the increase of the chromosome number. Other factors also include the splitting of the chromosome and increasing its number by one.

Note:
Karyotype is the total expression that includes the number, form, size, and grouping of chromosomes in a cell nucleus. If we see the structure of a chromosome it contains – pellicle, matrix, chromatids, chromomere, primary constriction and centromere, secondary constriction, satellite, and telomeres. Based on centromere position, a chromosome can be of $4$ types – metacentric, submetacentric, acrocentric, and telocentric.