A breeder investigates the inheritance of wing-case pattern in a species of beetle.
A beetle from a pure-breeding spotted strain was crossed with a beetle from a pure-breeding plain strain. All offspring in the first generation had spotted wing cases.
One of the first-generation beetles was then crossed with a beetle from the pure-breeding plain strain. The results are shown in the table.
| Wing-case phenotype | Number of offspring |
|---|---|
| spotted | 124 |
| plain | 116 |
The same first-generation beetle is crossed with another beetle from the pure-breeding plain strain, and 450 offspring are produced.
Use the genotypes of the two parents to calculate the number of these offspring expected to have plain wing cases.
State the term for the alternative versions of the gene involved in wing-case pattern.
Explain what the results of the two crosses show about dominance and the genotype of the first-generation beetles.
Suggest why the numbers of spotted and plain offspring in the second cross were not exactly equal.
186 exam-style questions on OCR GCSE Biology 5.1 Inheritance, covering 5.1.1 The genome, 5.1.2 Environment and phenotype, 5.1.3 Variants and mutations, 5.1.4 How genetic variants influence phenotype, 5.1.5 Asexual and sexual reproduction, 5.1.6 Haploid and diploid, 5.1.7 Meiotic cell division, 5.1.8 Single gene inheritance, 5.1.9 Predicting single gene crosses, 5.1.10 Sex determination, 5.1.11 Multiple gene inheritance, and 5.1.12 Development of our understanding of genetics. Each one has a worked solution and a mark scheme showing where the marks go.