February/March 2026 Paper 42

Eye colour in fruit flies is controlled by a single gene. The alleles for this gene are found on the X chromosome. Some fruit flies have red eyes and some have white eyes. The allele for red eye colour is dominant and is represented by the letter R. The allele for white eye colour is recessive and is represented by the letter r. A male fruit fly with the genotype $X^{R}Y$ and a female fruit fly with the genotype $X^r{X}^r$ are bred together. State the eye colour of the male and the female fruit flies.

State the term used to describe an individual who has two identical alleles of a particular gene.

Complete the Punnett square to determine the genotypes and phenotypic ratio of the offspring.

State the name of this type of monohybrid inheritance.

Figure 5.1 shows the chromosomes in a body cell of a fruit fly.

Use Figure 5.1 to complete the sentences about the genetic material in fruit flies.