Question

In a bird population using the ZW–ZZ sex determination system, if a ZZ male mates with a ZW female, what proportion of offspring would be expected to be female?

Options

• 50%

• 25%

• 75%

• 100%

Answer 1

In the ZW–ZZ system, females (ZW) are heterogametic, producing Z and W eggs in equal proportions. Males (ZZ) produce only Z sperm. The cross ZZ (male) × ZW (female) produces 50% ZZ (male) offspring and 50% ZW (female) offspring. Female offspring result from the union of a W egg with a Z sperm.