Question

The \[\dfrac{{ZZ}}{{ZW}}\] type of sex determination is seen in
A. Platypus
B. Snails
C. Cockroach
D. Peacock

Answer 1

Hint: The biological system is helpful in defining the sexual characteristics of an individual is called sex determination. when females are heterogametic, whereas in human beings' males are heterogametic this type of sex determination takes place.

Complete Answer:
In this system that is ZZ-ZW, the female is heterogametic (ZW), and the male is homogametic (ZZ). During gametogenesis that is fusion of gametes, half of the eggs have a Z chromosome and the other half will have a W chromosome. For males, all sperm contains a single Z chromosome. On fertilization of Z egg with Z sperm, a male with ZZ genotype is produced. When W egg fertilizes with Z sperm, a female with ZW type is produced. Snakes, butterflies, some amphibians, and some fishes also exhibit this type of sex determination.

Now let us gather information about given options:
- Platypus: It belongs to mammals. Males possess XY chromosomes and females possess XX chromosomes. So it has XX-XY type of sex determination pattern.
- Snails: It belongs to molluscs. XY – XO is seen in molluscs. During this type male individuals produce two differing types of gametes. Thus, the sperm determines the sex of the offspring. It involves two kinds of sex determining mechanisms; XO type and XY type.
- Cockroach: It belongs to insects. XX – XO is observed in a sizable number of insects e.g., Grasshopper. Number of chromosomes are different in male and female individuals.
- Peacock: It belongs to birds. ZZ-ZW is seen In birds, both the sexes possess two sex chromosomes. Unlike citizenry, the females contain heteromorphic sex chromosomes while the males have homomorphic sex chromosomes. due to having heteromorphic sex chromosomes, the females are heterogametic.

Hence the correct answer is option D.

Note: In birds, the males have two Z chromosomes (ZZ) and the females have one Z and one W chromosome (ZW). So, in females’ whichever allele is present on the single Z chromosome is fully expressed in the phenotype. When a cinnamon male is crossed with a normal female, then in offspring all the females will be cinnamon.