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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 ... 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 have no functional cones in the retina, which are essential for detecting light and color. Without functional cones, visual detail is diminished, resulting in an inability to perceive fine visual details.
Step 2
Use the Hardy-Weinberg equation to calculate the percentage of this population who are heterozygous for this disorder.
Answer
To calculate the percentage of heterozygous individuals using the Hardy-Weinberg equation, we denote:
Let p = frequency of the dominant allele, and q = frequency of the recessive allele.
Since 10% of the population is affected with achromatopsia, this corresponds to the frequency of the homozygous recessive genotype (q²). Therefore,
To find q, take the square root:
Using the relation p + q = 1,
The percentage of heterozygous individuals (2pq) can be calculated as:
Thus, approximately 43.2% of the population are heterozygous for this disorder.
Step 3
Explain why red-green colour blindness affects more men than women.
Answer
Red-green color blindness is linked to the X chromosome. Males have one X and one Y chromosome, while females have two X chromosomes. A single recessive allele on the X chromosome will cause color blindness in males. In females, two copies of the allele are needed for the condition to manifest, making it less frequent in females.
Step 4
Explain why people with red-green colour blindness are unable to distinguish between red and green.
Answer
People with red-green color blindness usually lack functioning green or red-sensitive cones. This absence or malfunction prevents them from detecting and differentiating between red and green wavelengths of light, leading to difficulty in distinguishing between these colors.
Step 5
Suggest how iPS cells could correct red-green colour blindness.
Answer
Induced pluripotent stem (iPS) cells could potentially differentiate into functional photoreceptor cells (cones) that are capable of sensing red and green wavelengths. These newly developed cones could then be integrated into the retina, restoring the ability to perceive color.
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 may offer long-term solutions by providing a continuous source of functional cones, unlike gene therapy, which may only provide a temporary fix. Additionally, iPS cells can be created from a patient's own tissues, minimizing the risk of rejection or immune response. Furthermore, they allow for the possibility of repeated treatments, enhancing effectiveness.