The gene for right handedness is dominant over the gene for left handedness. Most probable gene types of two right handed parents with left handed child is

Options

A. `R R xx r r`
B. `rrxx Rr`
C. `R R xx Rr`
D. `Rr xx Rr.`

Answer

To solve the question about the gene types of two right-handed parents with a left-handed child, we will follow these steps:

### Step 1: Understand the Genetics of Handedness
- Right-handedness (R) is dominant over left-handedness (r). This means that individuals with at least one dominant allele (R) will be right-handed, while only individuals with two recessive alleles (rr) will be left-handed.

### Step 2: Determine Possible Genotypes of Parents
- Since both parents are right-handed, their genotypes could either be homozygous dominant (RR) or heterozygous (Rr).
- However, for them to have a left-handed child (rr), at least one parent must carry the recessive allele (r). Therefore, both parents must be heterozygous (Rr).

### Step 3: Set Up a Punnett Square
- We will set up a Punnett square to visualize the genetic crosses between the two heterozygous parents (Rr x Rr).

```
R r
----------------
R | RR | Rr |
----------------
r | Rr | rr |
----------------
```

### Step 4: Analyze the Punnett Square
- From the Punnett square, we can see the possible genotypes of the offspring:
- 1 RR (right-handed)
- 2 Rr (right-handed)
- 1 rr (left-handed)

### Step 5: Calculate the Ratios
- The ratio of the offspring is:
- 3 right-handed (RR or Rr) : 1 left-handed (rr)

### Conclusion
- Therefore, the most probable genotypes of the two right-handed parents with a left-handed child are both heterozygous (Rr).

### Final Answer
- The answer is: Both parents are Rr (heterozygous for right-handedness).

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