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.