In a testcross involving `F_(1)` dihybrid flies, more parental-type offsping were produces than the recombinant-type offspring. This indicates

Options

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

Answer

To solve the question regarding the testcross involving F1 dihybrid flies, we need to analyze the information provided and understand the concepts of genetic linkage and inheritance patterns. Here’s a step-by-step breakdown of the solution:

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

**Hint:** A testcross helps determine the genotype of an individual with a dominant phenotype by crossing it with a recessive individual.

### Step 2: Analyze the Offspring Ratios
In the testcross, it was observed that more parental-type offspring were produced than recombinant-type offspring. This suggests that the genes controlling the traits are not assorting independently.

**Hint:** Parental-type offspring are those that resemble the parents, while recombinant-type offspring show new combinations of traits.

### Step 3: Linkage of Genes
When more parental-type offspring are produced, it indicates that the genes are linked. Linked genes are located close together on the same chromosome and tend to be inherited together, reducing the likelihood of crossing over during meiosis.

**Hint:** Linkage reduces the occurrence of recombination, leading to a higher proportion of parental combinations.

### Step 4: Evaluate the Options
Now, let’s evaluate the given options based on our analysis:
1. **Chromosomes fail to separate during meiosis** - This would lead to an abnormal number of chromosomes, not just more parental types.
2. **The two genes are linked and present on the same chromosome** - This is consistent with our observation of more parental-type offspring.
3. **Both characters are controlled by more than one gene** - This does not explain the observed offspring ratios.
4. **The two genes are located on two different chromosomes** - This would typically result in a 1:1:1:1 ratio of offspring types, not more parental types.

**Hint:** Consider how the arrangement of genes on chromosomes affects inheritance patterns.

### Step 5: Conclusion
Based on the analysis, the correct conclusion is that the two genes are linked and present on the same chromosome, which explains the higher number of parental-type offspring compared to recombinant-type offspring.

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