Sex determination in animals such as humans and insects is done using the XX-XO and XX-XY mechanisms. In some organisms ZZ-ZW mechanism of sex determination is seen.
Based on the given statement, answer the question given below.

Which of the following is incorrect regarding the ZW-ZZ type of sex determination?
[1 mark]

It occurs in birds and some reptiles

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Females are homogametic and males are heterogametic

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1:1 sex ratio is produced in offsprings

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All of these

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Solution

The correct option is 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.

Fertilisation of an egg with Z chromosome by a sperm with Z chromosome gives a zygote with ZZ chromosomes (male). Fertilisation of an egg with W chromosome by a sperm with Z chromosome yields a zygote with ZW chromosomes (female). The ratio of male (ZZ) and female (ZW) is found to be 1:1. This mechanism operates in some vertebrates (fishes, reptiles, and birds). Thus option b has the incorrect statement.

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