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People with complete achromatopsia have difficulty in seeing detail (lines 2–3) - AQA - A-Level Biology - Question 10 - 2018 - Paper 1
Question 10
People with complete achromatopsia have difficulty in seeing detail (lines 2–3). Explain why. Ten percent of the population on the Pacific island of Pingelap are a... show full transcript
Worked Solution & Example Answer:People with complete achromatopsia have difficulty in seeing detail (lines 2–3) - AQA - A-Level Biology - Question 10 - 2018 - Paper 1
Step 1
Explain why people with complete achromatopsia have difficulty in seeing detail.
Answer
People with complete achromatopsia lack functional cones in the retina, which are essential for daylight vision and color perception. This results in the reliance on rods, which are predominantly sensitive to light but do not provide sharp detail or color information. Consequently, their vision is generally poor, particularly in bright light conditions.
Step 2
Use the Hardy-Weinberg equation to calculate the percentage of this population who are heterozygous for this disorder.
Answer
Using the Hardy-Weinberg equation, we let 'q^2' represent the frequency of the recessive phenotype (achromatopsia). Given that 10% of the population is affected, we have:
Calculating 'q':
Using 'p + q = 1', we find:
To find the frequency of the heterozygous individuals (2pq):
Thus, approximately 43.2% of the population are heterozygous for achromatopsia.
Step 3
Explain why red-green colour blindness affects more men than women.
Answer
Red-green color blindness is often linked to the X chromosome. Males, having only one X chromosome, will express the condition if they inherit the affected allele. In contrast, females have two X chromosomes; hence, they would need to inherit two affected alleles to express the condition, making red-green color blindness significantly more prevalent in males.
Step 4
Explain why people with red-green colour blindness are unable to distinguish between red and green.
Answer
Individuals with red-green color blindness have non-functional cones responsible for detecting red and green wavelengths. This deficiency leads to a lack of signals sent to the brain regarding red and green stimuli, resulting in difficulty distinguishing these colors as well as other colors that rely on these cone types.
Step 5
Suggest how iPS cells could correct red-green colour blindness.
Answer
iPS cells can be used to generate functional retinal pigment cells that are capable of detecting light. By introducing these cells into the retina of individuals with red-green color blindness, it may be possible to restore the normal function of the cones that are not operational, thus correcting the color perception issue.
Step 6
Using the information from the passage, suggest and explain reasons why the use of iPS cells could have advantages over the use of gene therapy to correct red-green colour blindness.
Answer
The use of iPS cells offers several advantages over traditional gene therapy. Firstly, iPS cells can be patient-derived and thus have a lower risk of immune rejection compared to exogenous therapies. Moreover, they have the potential to differentiate into any cell type, providing a versatile and sustainable source of functional cells that can be continuously produced as needed. Additionally, iPS cell therapy may allow for more precise targeting and integration into the patient's retina, potentially leading to more effective restoration of vision.