A homozygous recessive with cd genes was crossed with dominant
(+ +). If their hybrid is test crossed and the following result was obtained
+ + - 900
cd - 880
+ d - 115
+ c - 105
than what will be the distance between genes c and d.

Options

A. 5.75 unit
B. 11 unit
C. 44 unit
D. 90 unit

Answer

To solve the problem of determining the distance between genes C and D based on the given progeny results, we can follow these steps:

### Step 1: Identify Parental and Recombinant Types
From the given progeny results:
- Parental types:
- + + (900)
- cd (880)
- Recombinant types:
- + d (115)
- + c (105)

### Step 2: Calculate Total Progeny
To find the total number of progeny, we add all the progeny counts together:
- Total = 900 (for + +) + 880 (for cd) + 115 (for + d) + 105 (for + c)
- Total = 900 + 880 + 115 + 105 = 2000

### Step 3: Calculate Total Recombinant Progeny
Next, we calculate the total number of recombinant progeny:
- Total Recombinant = + d (115) + + c (105)
- Total Recombinant = 115 + 105 = 220

### Step 4: Calculate the Distance Between Genes C and D
The distance between genes C and D can be calculated using the formula:
\[ \text{Distance (in map units)} = \left( \frac{\text{Number of Recombinant Progeny}}{\text{Total Progeny}} \right) \times 100 \]

Substituting the values we found:
\[ \text{Distance} = \left( \frac{220}{2000} \right) \times 100 \]

### Step 5: Simplify the Calculation
Now, we simplify the calculation:
\[ \text{Distance} = 0.11 \times 100 = 11 \text{ map units} \]

### Conclusion
The distance between genes C and D is **11 map units**.

---