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

Hint: Females are homogametic and males are heterogametic is only seen in XX-XY mechanism of sex determination.

Complete step by step answer:
-ZW - ZZ is a method of sex determination.
-The male has two homomorphic sex chromosomes – ZZ and is called homogametic.
-The female has two heteromorphic sex chromosomes – ZW and is called heterogametic.
-The female thus produces two types of eggs – one with Z and another with W. The males can produce only one type of sperm – Z.
-Fertilisation of an egg with Z chromosome with the sperm of Z chromosome will give rise to a zygote with ZZ chromosomes and that is a male. Both the chromosomes are the same so they are homogametic.
-Fertilisation of an egg with W chromosome with the sperm with Z chromosome will give rise to a zygote with ZW chromosomes and that is a female. The chromosomes are different so they are heterogametic.
-This mechanism of sex determination is seen in fishes, reptiles and birds.

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

Note:
-In roundworms and grasshopper, XX-XO mechanism of sex determination is seen where females are homogametic with XX and males carry only one sex chromosome and denoted as XO.
-Human follows XY-XX mechanisms of sex determination. In this case, male is heterogametic with the presence of XY sex chromosome and female have two copies of X-chromosomes – XX.
-The ratio of the number of X-chromosome to that of a complete set of autosome helps to determine the sex of Drosophila. The X/A value is 0.5 for a normal male and the value 1 denotes a female drosophila.