Inheritance · Paper 2 — Free Biology SL Practice Questions

In pea plants, the allele for purple flower colour ($P$) is dominant over the allele for white flower colour ($p$). A farmer crosses a heterozygous purple-flowered plant with a white-flowered plant.

A geneticist is studying a family with a history of cystic fibrosis (CF), an autosomal recessive disorder caused by mutations in the CFTR gene. The pedigree below shows the inheritance of CF across three generations. - Individuals I-1 and I-2 are unaffected. - Individual II-1 is affected with CF and is the child of I-1 and I-2. - Individual II-2 is an unaffected child of I-1 and I-2. - Individual II-3 is unaffected; their brother, II-4, is affected with CF. - Individual III-1 is the unaffected child of II-2 and II-3. Use the allele symbols $F$ (dominant, normal) and $f$ (recessive, CF).

In a breeding experiment an agricultural research station, a true-breeding strain of pea plants with round, yellow seeds ($RRYY$) was crossed with a true-breeding strain with wrinkled, green seeds ($rryy$). The $F_1$ generation all had round, yellow seeds. The $F_1$ plants were then self-fertilized to produce an $F_2$ generation of 320 seeds. The following results were recorded: - Round, yellow seeds: 175 - Round, green seeds: 55 - Wrinkled, yellow seeds: 65 - Wrinkled, green seeds: 25