X - linked traits ( Punnett Square basics ) - YouTube - Free Printable

Problem Description:

The image shows a Punnett square for a sex-linked trait, specifically hemophilia, which is caused by a recessive allele located on the X chromosome. The task involves analyzing the inheritance pattern when a heterozygous female carrier (X^HX^h) mates with an unaffected male (X^HY). The goal is to determine the genotypes and phenotypes of the offspring.

Key Information:

1. Hemophilia is a sex-linked recessive disorder.
- X^H: Normal allele (dominant)
- X^h: Mutated allele causing hemophilia (recessive)

2. Parents' Genotypes:
- Female: Heterozygous carrier (X^HX^h)
- Male: Unaffected (X^HY)

3. Punnett Square:
The Punnett square is partially filled, showing the possible combinations of alleles from the parents.

Step-by-Step Solution:

#### 1. Identify the Gametes:
- Female (X^HX^h):
Since the female is heterozygous, she can produce two types of gametes:
- X^H (carrying the normal allele)
- X^h (carrying the mutated allele)

- Male (X^HY):
Since the male is unaffected, he can produce two types of gametes:
- X^H (carrying the normal allele)
- Y (carrying no X chromosome)

#### 2. Construct the Punnett Square:
The Punnett square is used to determine all possible combinations of alleles from the parents. The female's gametes are placed along the top, and the male's gametes are placed along the left side.

| | X^H | X^h |
|-------|---------------|---------------|
| X^H | X^HX^H | X^HX^h |
| Y | X^HY | X^hY |

#### 3. Analyze the Offspring Genotypes:
- Top Left (X^HX^H):
- Genotype: X^HX^H
- Phenotype: Unaffected female (homozygous dominant)

- Top Right (X^HX^h):
- Genotype: X^HX^h
- Phenotype: Carrier female (heterozygous; appears unaffected but can pass the mutated allele to her offspring)

- Bottom Left (X^HY):
- Genotype: X^HY
- Phenotype: Unaffected male (only one X chromosome, and it carries the normal allele)

- Bottom Right (X^hY):
- Genotype: X^hY
- Phenotype: Affected male (hemophiliac; only one X chromosome, and it carries the mutated allele)

#### 4. Summary of Offspring:
- Females:
- X^HX^H: Unaffected (normal)
- X^HX^h: Carrier (appears normal but can pass the mutated allele)

- Males:
- X^HY: Unaffected (normal)
- X^hY: Affected (hemophiliac)

Final Answer:

The Punnett square fully completed is as follows:

| | X^H | X^h |
|-------|---------------|---------------|
| X^H | X^HX^H | X^HX^h |
| Y | X^HY | X^hY |

The genotypes and phenotypes of the offspring are:
- Unaffected females (X^HX^H): 50%
- Carrier females (X^HX^h): 50%
- Unaffected males (X^HY): 50%
- Affected males (X^hY): 50%

Thus, the probability distribution of the offspring is:
- Unaffected females: 25%
- Carrier females: 25%
- Unaffected males: 25%
- Affected males: 25%

$$
\boxed{\text{Unaffected females: 25%, Carrier females: 25%, Unaffected males: 25%, Affected males: 25%}}
$$