QUESTION 7 (3 marks)
The sex of chickens is determined by Z and W chromosomes. Chickens that inherit two Z chromosomes (ZZ) are male, while chickens with one Z chromosome and one W chromosome (ZW) are female. A barred feather pattern is a sex-linked dominant trait inherited on the Z chromosome. A male chicken that was heterozygous for the barred feather pattern was bred with a female chicken that did not have the trait. They produced eight offspring. Predict the number of offspring with the barred feather pattern. Justify your response using a Punnett square.
QCAA guide · typeset solution
QCAA sample response and mark allocation
7 |  4 Number of offspring with barred pattern 0.5 8 × 4 offspring | • identifies parental genotypes [1 mark] • provides an appropriate Punnett square [1 mark] • predicts number of offspring with the barred feather pattern [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.