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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. [3 marks] Ten percent of the population on the Pacific island of Pin... 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 their retinas, typically having only rods. Rods are sensitive to light but do not detect color, leading to poor visual acuity and difficulty seeing fine details, especially in bright light.
Step 2
Use the Hardy-Weinberg equation to calculate the percentage of this population who are heterozygous for this disorder.
Answer
Given that 10% of the population is affected, thus representing the genotype frequency of the homozygous recessive phenotype, we can set q² = 0.10. Therefore, q = √0.10 ≈ 0.316. Using the Hardy-Weinberg principle, we have p + q = 1, thus p ≈ 1 - 0.316 = 0.684. The frequency of heterozygous carriers (2pq) is calculated as:
Hence, 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 linked to a gene on the X chromosome. Males have one X chromosome, while females have two; thus, males are more likely to express the trait if they inherit the affected X chromosome. Females have to inherit two affected X chromosomes to exhibit the condition, making it more common in males.
Step 4
Explain why people with red-green colour blindness are unable to distinguish between red and green, and also between other colours.
Answer
Individuals with red-green color blindness have non-functional green-sensitive or red-sensitive cones in their eyes, leading to difficulties in perceiving red and green wavelengths of light. This impairment results in an inability to differentiate between these colors, as well as between other colors that combine red and green hues.
Step 5
Suggest how iPS cells could correct red-green colour blindness.
Answer
Induced pluripotent stem cells (iPS cells) could be directed to differentiate into functional photoreceptor cells that properly express the missing pigments. By doing so, these cells could potentially restore the necessary color detection capabilities, correcting the visual impairment associated with red-green color blindness.
Step 6
Using the information from the passage, suggest and explain reasons why the use of iPS cells could have advantages over gene therapy to correct red-green colour blindness.
Answer
Using iPS cells may offer long-term solutions compared to gene therapy because iPS cells can proliferate and potentially provide a continuous supply of corrected cells. Furthermore, iPS cells could minimize rejection risks associated with foreign cell introduction in gene therapy. Additionally, iPS cells allow for more precise genetic corrections, potentially offering a more durable correction of the condition.