Albinism, the total lack of melanin pigment, it due to a recessive
gene a. A normal man and a normal woman both of whom had one albino parent, marry. What is the probaility of them having an albino child ?

Options

A. 0.5
B. 0.25
C. 0.75
D. All

Answer

To solve the problem of determining the probability of a normal man and a normal woman, both of whom had one albino parent, having an albino child, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Genotypes of the Parents:**
- Albinism is caused by a recessive gene represented as 'a'.
- A normal individual with one albino parent must have the genotype 'Aa' (heterozygous) because they carry one normal allele (A) and one albino allele (a).
- Therefore, both the normal man and the normal woman have the genotype 'Aa'.

2. **Determine the Gametes:**
- Each parent can produce two types of gametes: 'A' (normal allele) and 'a' (albino allele).
- Thus, the gametes from both parents are:
- Male: A, a
- Female: A, a

3. **Set Up a Punnett Square:**
- Create a Punnett square to visualize the possible combinations of gametes from both parents.
- The Punnett square will look like this:

```
A a
------------
A | AA | Aa |
------------
a | Aa | aa |
```

4. **Analyze the Offspring Genotypes:**
- From the Punnett square, we can see the possible genotypes of the offspring:
- AA (normal)
- Aa (normal)
- Aa (normal)
- aa (albino)

5. **Count the Genotypic Ratios:**
- The genotypic ratio is:
- 1 AA : 2 Aa : 1 aa
- This means there are 3 normal offspring (AA and Aa) and 1 albino offspring (aa).

6. **Calculate the Probability of Having an Albino Child:**
- The probability of having an albino child (genotype 'aa') is 1 out of 4 possible offspring.
- Therefore, the probability is:
- Probability = Number of albino offspring / Total offspring = 1/4 = 0.25.

### Final Answer:
The probability of the normal man and woman having an albino child is **0.25**.

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