Title: Sex-Linked Punnett Square Practice and Inheritance Patterns
The Correct Answer and Explanation is:
Based on the provided image of the biology worksheet, here are the correct answers and a detailed explanation for the “Sex-Linked Punnett Square Practice” questions.
Answer:
For question 8, Bob inherited the gene for color blindness from his mother. For question 9, the father determines the biological sex of a baby.
Explanation:
Bob inherited the gene for color blindness exclusively from his mother. This is because color blindness is a classic example of an X-linked recessive trait, which means the gene responsible for the condition is located on the X chromosome. As a male, Bob has one X and one Y chromosome (XY). He must inherit the Y chromosome from his father to be male, and he inherits his only X chromosome from his mother. Since Bob is color blind, his X chromosome must carry the recessive allele for the trait.
We know his father is not color blind, so the father’s genotype is XBY, with “B” being the dominant allele for normal vision. The father passed the Y chromosome to Bob, not an X. Bob’s mother has normal vision but must be a carrier of the recessive gene, making her genotype XBXb. She passed her Xb chromosome to Bob. A Punnett square would show the mother’s possible eggs (XB and Xb) and the father’s possible sperm (XB and Y). This cross reveals a 25% probability of having a color blind son (XbY), which confirms that the mother is the parent who passed the trait to Bob.
For the second question, the father determines the biological sex of a baby. This is proven by a Punnett square showing the parents’ sex chromosomes. The mother has two X chromosomes (XX), meaning every egg she produces will contain one X chromosome. The father has one X and one Y chromosome (XY), so his sperm can carry either an X or a Y. If a sperm containing an X chromosome fertilizes the egg, the resulting offspring will have an XX genotype and be female. If a sperm containing a Y chromosome fertilizes the egg, the offspring will have an XY genotype and be male. Since the mother can only contribute an X chromosome, it is the father’s contribution of either an X or a Y that ultimately determines the baby’s sex.
