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Red-green colour blindness is caused by an allele that is sex-linked and recessive - Scottish Highers Human Biology - Question 13 - 2022
Question 13
Red-green colour blindness is caused by an allele that is sex-linked and recessive. A woman's father has the allele for colour blindness, but her mother does not. Th... show full transcript
Worked Solution & Example Answer:Red-green colour blindness is caused by an allele that is sex-linked and recessive - Scottish Highers Human Biology - Question 13 - 2022
Step 1
Understand the Genetics Involved
Answer
Red-green colour blindness is a sex-linked recessive trait. It is carried on the X chromosome. In this scenario, the woman (let's denote her as X^c X, where X^c is the X chromosome with the allele for colour blindness) has a father with colour blindness (X^c Y) and a mother without it (X X). This means she is a carrier for the allele for colour blindness, as she inherited her mother's X chromosome without the allele.
Step 2
Step 3
Perform a Punnett Square Analysis
Answer
Using a Punnett square to determine the probability of their son inheriting the colour blindness allele:
| X | Y |
-------------------
X^c | X^cX | X^cY |
-------------------
X | X X | XY |
In this Punnett square:
- From the X^c (mother): X^cX (daughter - carrier) and X^cY (son - colour blind)
- From the X (mother): X X (daughter - normal) and XY (son - normal)
There are two possible sons: 1 with colour blindness and 1 without.
Step 4