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Read the following passage - AQA - A-Level Biology - Question 10 - 2018 - Paper 2
Question 10
Read the following passage. Complete achromatopsia is a form of complete colour blindness. It is caused by having only rods and no functional cone cells. People wit... show full transcript
Worked Solution & Example Answer:Read the following passage - AQA - A-Level Biology - Question 10 - 2018 - Paper 2
Step 1
People with complete achromatopsia have difficulty in seeing detail (lines 2–3).
Answer
People with complete achromatopsia lack functional cone cells, which are responsible for color vision and fine detail perception. This results in reliance on rod cells, which are more sensitive to light but do not perceive color. Therefore, individuals cannot distinguish between colors and have difficulty seeing in detail.
Step 2
Use the Hardy-Weinberg equation to calculate the percentage of this population who are heterozygous for this disorder. Show your working.
Answer
Let the allele for complete achromatopsia be represented by 'q'. Given that 10% of the population (p + q = 1) is affected, we have:
Thus, to find 'q', we compute:
Now, using the Hardy-Weinberg equation, we can find 'p':
The percentage of heterozygous carriers is given by:
Therefore, approximately 43.2% of the population are heterozygous for this disorder.
Step 3
Red-green colour blindness affects more men than women (lines 7–8).
Answer
Red-green color blindness is linked to a recessive allele on the X chromosome. Men, with only one X chromosome, are affected if they inherit the allele. In contrast, women have two X chromosomes, meaning they would require two copies of the allele to express the condition. This disparity leads to a higher prevalence of red-green color blindness in men compared to women.
Step 4
People with red-green colour blindness are unable to distinguish between red and green, and also between other colours (lines 8–10).
Answer
Individuals with red-green color blindness have non-functional green-sensitive cones. This deficiency prevents them from detecting green light, which is essential for distinguishing between red and green colors. As a result, they may confuse red and green with other colors due to the lack of specific color detection.
Step 5
Suggest how iPS cells could correct red-green colour blindness.
Answer
Induced pluripotent stem cells (iPS cells) can potentially be differentiated into functional photoreceptor cells, which include the green-sensitive cones. By introducing healthy copies of the genes necessary for the formation and function of these cones, iPS cells could restore the ability to perceive red and green light, thus correcting the color blindness.
Step 6
The use of iPS cells could have advantages over the use of gene therapy to correct red-green colour blindness (lines 19–20).
Answer
iPS cells can provide long-term treatment solutions by continuously supplying functional photoreceptor cells, mitigating the need for repeat treatments. Additionally, iPS cells have a lower risk of rejection compared to traditional gene therapy, which may introduce foreign DNA. Lastly, iPS cells can be tailored to an individual’s specific needs, enhancing the overall effectiveness of the treatment.