Chapter+13

Data-based question: gene linkage in //Zea mays// page 159 (2012 edition)

1. Coloured, starchy both dominant traits Cc White, waxy recessive traits Ss F1 are all CcSs so F1 x F1 CcSs x CcSs produces typical dihybrid ratio of 9 coloured starchy: 3 coloured waxy: 3 white starchy: 1 white waxy in F2.

2. The actual frequencies do not follow the 9:3:3:1 ratio and so the genes must be linked as they differ from the theoretical ratio for dihybrid crosses.

3. Coloured, shrunken CCnn

White, non-shrinken ccNN

F1 coloured, non-shrunken is CcNn are test-crossed with homozygous recessive: ccnn

CcNn x ccnn

Typical ratio of 1 coloured non-shrunken: 1 coloured shrunken: 1 white non-shrunken: 1 white shrunken

4. Actual frequencies differ from typical ratio of 1:1:1:1 so genes must be linked.

5. If starchy/waxy and non-shrunken/shrunken are both linked to colour, then they must also be linked to each other.