Question

In Drosophila female has a pair of chromosomes
A. ZZ
B. XX
C. YY
D. ZW

Answer 1

Chromosomes are the long molecules having some or all the genetic material of an organism. It is the package of DNA found in the nucleus of a cell.

Complete Answer:
Chromosome:
- The term ‘Chromosome’ was introduced by Waldeyer in 1888. Chromosomes are the thread-like structures that are present inside the nucleus of plant cells and animal cells.
- Chromosomes consist of protein and a molecule of DNA ( Deoxyribonucleic acid).
- Chromosomes are only visible during the time of cell division.
- Each chromosome is divided into two sections from the centromere. These sections are- p-arm q-arm.

In humans, chromosomes can be divided into two categories:
1. Autosomes (body chromosomes)
2. Allosomes ( sex chromosomes)

1. Autosomes: These chromosomes are present in the somatic cells i.e all the body cells. Their ploidy level is diploid i.e. they are paired chromosomes. These chromosomes are represented by ‘2n’.
2. Allosomes: Allosomes are the chromosomes that are present in the sex chromosomes i.e male gamete (sperms) and female gamete (ovum). Their ploidy level is haploid i.e. they are a single set of chromosomes. These chromosomes are represented by ‘n’.

Female Drosophila melanogaster:
Drosophila melanogaster is a species of fly. It has four pairs of chromosomes – two pairs of autosomes that are large in size and one pair of allosomes that are small in size.
Female has two X chromosomes i.e. XX and male has one X and one Y chromosome i.e. XY.

Hence, option B is the correct option for this answer.

Note: Without chromosomes, crossing over is not possible. If crossing over does not occur, then there will be no variation in the species. Chromosomes contain genes in the beaded form. And genes are the unit of inheritance which are responsible for the passage of characters from one generation to the next generation.