In birds, which sex chromosome determines the sex of the offspring?
Z chromosome
W chromosome
X chromosome
Y chromosome
In birds, sex is determined by the presence of sex chromosomes, just like in mammals. However, the sex chromosomes in birds are different from those in mammals. In birds, females have two different sex chromosomes called Z and W. Males, on the other hand, have two identical Z chromosomes. The presence of the ZW chromosome pair in a bird determines its sex.
If an egg is fertilized by a sperm carrying a Z chromosome, the resulting offspring will develop as a male (ZZ), while if the egg is fertilized by a sperm carrying a W chromosome, the offspring will develop as a female (ZW). Therefore, it is the presence or absence of the W chromosome that determines the sex of the offspring in birds.
Option 1 is the correct answer.