Question

Which of the following is incorrect regarding ZW-ZZ type of sex determination?

• A. It occurs in birds and some reptiles.
• B. Females are homogametic and males are heterogametic.
• C. Sex ratio is produced in the offspring.
• D. All of the above
  

Answer 1

Answer: (B)

Females are homogametic and males are heterogametic.

• In ZW - ZZ type of sex determination, the male has two homomorphic sex chromosomes (ZZ) and is homogametic, and the female has two heteromorphic sex chromosomes (ZW) and is heterogametic.
• There are, thus, two types of eggs: with Z and with W, and only one type of sperms, le., each with Z.

• Fertilisation of an egg with a Z chromosome by a sperm with a Z chromosome gives a zygote with ZZ chromosomes (male).
• Fertilisation of an egg with a W chromosome by a sperm with a Z chromosome yields a zygote with ZW chromosomes (female).
• This mechanism operates in some vertebrates (fishes, reptiles and birds).

So, the correct answer is 'Females are homogametic and males are heterogametic'.