In a dihybrid cross, when would the proportion of parental gene combinations be much higher than non-parental types, as experimentally shown by Morgan and his group?

Explanation

To answer the question regarding when the proportion of parental gene combinations would be much higher than non-parental types in a dihybrid cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Dihybrid Cross**: A dihybrid cross involves two traits, each represented by two alleles. For example, consider two traits: body color (brown vs. yellow) and eye color (red vs. white) in Drosophila (fruit flies).

2. **Identifying Parental and Non-parental Combinations**: In the given example, we have:
- Parental combinations:
...