Question

1. amy claims that genes are linked in dihybrid crosses. is amy right or wrong? explain.
2. how can the phenotypic ratio of a dihybrid cross be derived using the multiplication rule of probability?

Explanation:

1. Genes can be linked or un - linked in dihybrid crosses. Linked genes do not assort independently during meiosis. If genes are on the same chromosome, they tend to be inherited together. So Amy can be right if the genes in question are on the same chromosome.
2. In a dihybrid cross with un - linked genes, each trait is considered separately. For a single gene cross (e.g., Aa x Aa), the phenotypic ratio is 3:1. Using the multiplication rule of probability, for two un - linked genes (AaBb x AaBb), the phenotypic ratio is the product of the ratios of each single - gene cross. So (3:1) x (3:1) = 9:3:3:1.

Answer:

1. Amy can be right if the genes are on the same chromosome and linked.
2. Consider each single - gene cross ratio (3:1 for Aa x Aa) and multiply them. For AaBb x AaBb, (3:1) x (3:1) gives 9:3:3:1 phenotypic ratio.