ICSE Class 10 Answered

Types of sex determination systems:

Depending on the presence of similar gametes (homogametic) or dissimilar gametes (heterogametic), following are the systems of sex determination:

XX-XY type:

Females are homogametic as they produce only one type of egg, (A+X). Males are heterogametic as they produce two types of sperms, (A+X) and (A+Y). The sex ratio produced in the progeny is 1:1. Examples: Most insects like fruitfly Drosophila and mammals including human beings.

XX-XO type:

Females are homogametic, (A+X). Males are heterogametic (A+X) and (A+O). The sex ratio produced in the progeny is 1:1. Examples: Roundworms and some insects such as true bugs, grasshoppers and cockroaches.

ZW-ZZ type:

Females are heterogametic, (A+Z) and (A+W). Males are homogametic, (A+Z). The sex ratio produced in the progeny is 1:1. Examples: Birds and some reptiles.

ZO-ZZ type:

Females are heterogametic, (A+Z) and (A+O). Males are homogametic, (A+Z). The sex ratio produced in the progeny is 1:1. Examples: Butterflies and moths.