There are 4 pairs of chromosomes in a Drosophila. The linkage groups present in it are

The correct answer is four.

Step-by-step Explanation:

1. Definition of a Linkage Group:
A linkage group is a set of genes that are located on the same chromosome. Because these genes reside on the same chromosome structure, they are physically linked and tend to be inherited together during meiosis, rather than assorting independently.

2. Linkage Groups and Chromosome Numbers:
Since all genes on a single chromosome constitute one linkage group, the total number of linkage groups in any organism is equal to its haploid number of chromosomes. This relationship is represented as:

$\text{Number of linkage groups}=n$

where $n$ is the haploid number of chromosomes (or the number of chromosome pairs in diploid organisms).

3. Calculation for Drosophila:
Drosophila (the common fruit fly) is a diploid organism containing 4 pairs of chromosomes. This means:
Diploid chromosome number:

$2n=8$

Haploid chromosome number (the number of pairs):

$n=4$

Therefore, the number of linkage groups present in Drosophila is exactly 4.