A test cross of `F_(1)` flies +a/+b produced the followings,
++/ab(R) 9`" "` ab/ab(R)9
+b/ab(R) 41`" "`a+/ab(R)41
This cross represents

Options

A. Trans configuration
B. Cis configuration
C. Complete linkage
D. No crossing over

Answer

To solve the problem, we need to analyze the given test cross results and determine the type of genetic configuration represented by the F1 flies with the genotype +a/+b.

### Step-by-Step Solution:

1. **Understanding the Test Cross**:
- A test cross involves crossing an individual with a homozygous recessive individual to determine the genotype of the former. In this case, the F1 flies have the genotype +a/+b.

2. **Interpreting the Results**:
- The offspring from the test cross are:
- ++/ab (R) - 9
- ab/ab (R) - 90
- +b/ab (R) - 41
- a+/ab (R) - 41
- The numbers next to each genotype indicate the frequency of each type of offspring.

3. **Identifying Recombinants and Parental Types**:
- The parental types are those that match the original F1 genotype (+a/+b) and the homozygous recessive (ab/ab).
- The recombinant types are those that differ from the parental types, which in this case are ++/ab, +b/ab, and a+/ab.

4. **Calculating Recombinant Frequencies**:
- The total number of offspring is: 9 (++) + 90 (ab) + 41 (+b) + 41 (a+) = 181.
- The recombinant types are ++/ab (9) + +b/ab (41) + a+/ab (41) = 91.
- The recombinant frequency = (Number of recombinants / Total offspring) = 91 / 181.

5. **Determining Linkage**:
- A high number of parental types (90) compared to the number of recombinants (91) suggests that the genes are linked.
- If there were no linkage, we would expect a more even distribution of offspring types.

6. **Identifying the Configuration**:
- The F1 genotype +a/+b indicates that the two dominant alleles are on different homologous chromosomes (trans configuration).
- In trans configuration, the dominant alleles are not on the same chromosome, which is consistent with the observed offspring ratios.

7. **Conclusion**:
- Based on the analysis, the test cross represents a trans configuration.

### Final Answer:
The cross represents **trans configuration**.

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