Question

Sex chromosomes of a female bird are represented by
(a) XO
(b) XX
(c) XY
(d) ZZ
(e) ZW

Answer 1

Birds, some fish and crustaceans like the enormous river prawn, some insects (including butterflies and moths), and some reptiles, including komodo dragons come under this category of sex determination.

Complete answer:
The sex chromosomes in birds are designated the letters Z and W. In this case the male is homomorphic (ZZ) and the female is heteromorphic (ZW). It is seen that in most birds the Z chromosome is a large chromosome, usually the fourth or fifth largest, and it contains almost all the known sex-linked genes. Additionally, it is also known that the W chromosome is generally a much smaller microchromosome, containing a high proportion of repeat sequence DNA.
On the contrary, it is still unknown whether it is the presence of the W chromosome that induces female features, or whether instead, it is the duplication of the Z chromosome that induces male ones. Also unlike mammals, no birds with a double W chromosome (ZZW) or a single Z (Z0) are discovered.

Additional information: Gynandromorphism is a phenomenon that has been known to exist in insects, crustaceans, and birds. It is mainly a rare and remarkable type of mutation that results in an organism being of both sexes. However, it cannot be termed as hermaphrodite (characterized by both or ambiguous genitalia). Instead, there is another phenomenon in which the sexes and their associated cells are evenly divided among the organism, resulting in parts of the body and even the brain being entirely female or male.
This phenomenon is best observed in bilateral gynandromorphs, in which the genders are evenly split right down the middle, causing two exact halves of the same creature to be of the opposite sex.
So, the correct answer is ‘(e) ZW’.

Note: In contrast to the XY sex-determination system as seen in humans and the X0 sex-determination system as seen in grasshoppers, where the sperm determines the sex, within the ZW system where the sex of the offspring is determined by the ovum.