Question

In breeding pure-breeding large and small strains of mice, you cross individuals of each strain and note that their offspring are intermediate in size. Two models (explanations) to account for this result are (1) that body size in these strains is due to one gene with alleles that show incomplete dominance and (2) that body size is a polygenic trait. How could you distinguish between these models?

1) Intercross the F1 and see if there is a range of sizes in the F₂ (consistent with the incomplete dominance model) or if the F₂ contains two size classes (consistent with the polygenic model).
2) Intercross the F1 and see if there is a range of sizes in the F₂ (consistent with the incomplete dominance model) or if the F₂ contains only three size classes (consistent with the polygenic model).
3) Body size is known to be an incompletely dominant trait.
4) Intercross the F1 and see if the F₂ contains three size classes (consistent with the incomplete dominance model) or if there is a range of sizes (consistent with the polygenic model).

Answer 1

To distinguish between the incomplete dominance and polygenic models for the intermediate size of offspring, one can intercross the F1 generation and observe the characteristics of the F2 generation.

Step-by-step explanation:

The most effective way to distinguish between the two models (explanations) for the intermediate size of the offspring would be to intercross the F1 generation and observe the characteristics of the F2 generation.

If the F2 generation contains a range of sizes, it would be consistent with the incomplete dominance model, where body size is determined by one gene with alleles that show incomplete dominance.

On the other hand, if the F2 generation contains two or three distinct size classes, it would support the polygenic model, where body size is controlled by multiple genes.