Inheritance · Paper 2 — Free Biology HL Practice Questions

In a species of fruit fly (Drosophila melanogaster), grey body colour ($G$) is dominant over black body colour ($g$). A female fly heterozygous for body colour is crossed with a male fly that has a black body. In a large experiment, 800 offspring are produced: 560 have grey bodies and 240 have black bodies.

A genetic counsellor analyses a family pedigree for a rare autosomal recessive disorder controlled by a single gene (alleles $D$ and $d$). The disorder causes severe metabolic dysfunction and is often fatal in early childhood. An affected individual (genotype $dd$) has two unaffected parents. The affected individual marries an unaffected woman with no known family history of the disorder.