May/June 2026 Paper 43

Figure 4.1 shows a cross between a chicken that is pure-breeding for white feathers and a chicken that is pure-breeding for black feathers. All of the offspring have black and white feathers that are described as speckled.

The allele for white feathers is represented by ${\mathrm{F}}^W$. The allele for black feathers is represented by ${\mathrm{F}}^B$. The genotype of all of the speckled chicken offspring is ${\mathrm{F}}^W{\mathrm{F}}^B$. State the term that is used to describe the situation where both alleles in heterozygous organisms contribute to the phenotype.

Two of the speckled chicken offspring were bred together. Complete the Punnett square to determine the genotypes and phenotypic ratio of the offspring from this cross.

Chickens can be farmed intensively. Describe two disadvantages of intensive livestock production.

DNA controls cell function by controlling the production of proteins. Explain how a protein is made.