Question

Sex chromosomes of a female bird are
A. XO
B. ZZ
C. ZW
D. XX
E. XY

Answer 1

Chromosomes are organized packaged structures of DNA that are found in the nucleus of the cell. The number of chromosomes varies according to organisms. These facilitate cell division and replication. Chromosomes are of two types – autosomes and allosomes. Somatic cells are diploid whereas gametes are haploid. This means that there is one copy of chromosomes in gametes and two copies in somatic cells.

Complete answer:
The sexes of unisexual organisms can be identified by the type of chromosomes present in them.
XO: Incorrect answer
The XO sex-determination system is present in silverfish, dragonflies, grasshoppers, cockroaches, some nematodes, crustaceans, molluscs, and bony fish. In this type of system, the organisms with XX chromosomes are recognized as females whereas the organisms with X0 chromosomes are recognized as males.
ZZ: Correct Answer
The ZZ-ZW system is found in birds. The homogametic ZZ system is found in female birds. Other organisms that follow this system of sex determination are moths, butterflies, some fish, and some crustaceans.
ZW: Correct answer
Males of organisms following the ZZ-ZW system have the ZW chromosomes. Birds follow this system of sex determination.
XX: Incorrect Answer
Females of the XX-XY system, like human females, have the XX chromosomes.
XY: Incorrect Answer
Males of the XX-XY system have the XY chromosomes

Hence, the correct answer is option (B and C).

Note: X chromosome inactivation happens in females having the XX chromosomes. This stops the expression of duplicate genes.