In a testcross involving `"F"1` dihybrid flies, more parental-type offspring were produced than the recombinant-type offspring. This indicates:

Options

A. Both of the characters are controlled by more than one gene
B. The two genes are located on two difference chromosomes
C. Chromosomes failed to separate during meiosis
D. The two genes are linked and present on the same chromosome

Answer

To solve the question, we need to analyze the implications of the results from the testcross involving F1 dihybrid flies. Here’s a step-by-step breakdown:

### Step 1: Understand the Testcross
A testcross is performed by crossing an individual with a homozygous recessive individual to determine the genotype of the individual being tested. In this case, we are dealing with F1 dihybrid flies, which means they are heterozygous for two traits.

**Hint:** Remember that a testcross helps reveal the genotype of an organism based on the phenotypes of the offspring.

### Step 2: Analyze the Offspring Ratios
The question states that more parental-type offspring were produced than recombinant-type offspring. This suggests that the traits are not assorting independently, which would typically yield a 1:1:1:1 ratio in a dihybrid cross.

**Hint:** Think about what it means when the parental types outnumber the recombinant types in the offspring.

### Step 3: Consider Genetic Linkage
When two genes are located close to each other on the same chromosome, they tend to be inherited together, a phenomenon known as genetic linkage. This results in a higher number of parental-type offspring compared to recombinant types.

**Hint:** Recall the concept of genetic linkage and how it affects inheritance patterns.

### Step 4: Evaluate the Options
Now, let’s evaluate the provided options:
1. Both characters are controlled by more than one gene - This is incorrect as it would lead to independent assortment.
2. Two genes are located on two different chromosomes - This is also incorrect as it would not result in more parental types.
3. Chromosomes failed to separate during meiosis - This is unlikely and would not specifically explain the observed results.
4. Two genes are linked and present on the same chromosome - This is correct as it explains the higher number of parental-type offspring.

**Hint:** Consider which option aligns with the principles of inheritance and the observed results.

### Step 5: Conclusion
The correct conclusion from the analysis is that the two genes are linked and present on the same chromosome, leading to more parental-type offspring than recombinant-type offspring.

**Final Answer:** The two genes are linked and present on the same chromosome.