Bob is color blind, but he knows that neither of his parents werecolor blind. He is wondering if he received the gene for color blindness from his mother, his father, or both of his parents.What would you tell Bob? Show a Punnett square to prove your answer!
The Correct Answer and Explanation is :
Answer:
Bob inherited the gene for color blindness from his mother. Since color blindness is an X-linked recessive trait, males (who have only one X chromosome) inherit the condition from their mothers, who may be carriers of the gene.
Punnett Square Analysis:
Color blindness is caused by a recessive allele located on the X chromosome. Since males have one X and one Y chromosome (XY), they inherit their X chromosome from their mother and their Y chromosome from their father.
- Father’s Genotype: Since Bob’s father is not color blind, his genotype must be XY (normal X chromosome).
- Mother’s Genotype: Since Bob’s mother is not color blind but has a son with color blindness, she must be a carrier (XᴺXᶜ), meaning she has one normal X chromosome and one affected X chromosome.
The Punnett square below shows the possible genetic combinations for their children:
| Xᴺ (Mother’s Normal X) | Xᶜ (Mother’s Color Blind X) | |
|---|---|---|
| X (Father’s Normal X) | XᴺX (Normal Daughter) | XᶜX (Carrier Daughter) |
| Y (Father’s Y Chromosome) | XᴺY (Normal Son) | XᶜY (Color Blind Son) |
Explanation:
- Daughters (XX):
- 50% chance of being normal (XᴺXᴺ).
- 50% chance of being a carrier (XᴺXᶜ), meaning they won’t be color blind but can pass the gene to their children.
- Sons (XY):
- 50% chance of being normal (XᴺY).
- 50% chance of being color blind (XᶜY), like Bob.
Since Bob is color blind (XᶜY), he must have inherited his Xᶜ chromosome from his mother, as his father can only pass a Y chromosome to his sons.
Thus, Bob’s mother is a carrier of the gene, and his father did not pass on color blindness to him.
Conclusion:
Bob inherited the gene for color blindness from his mother, who is a carrier, while his father had no role in passing down the trait.
Here is the Punnett square diagram illustrating the inheritance of X-linked color blindness. This shows how Bob inherited the gene from his mother, who is a carrier, while his father contributed a normal Y chromosome. Let me know if you need any modifications or further explanations!
