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Alzheimer's disease (AD) is a non-reversible brain disorder that develops over a number of years - AQA - A-Level Biology - Question 10 - 2017 - Paper 2
Question 10
Alzheimer's disease (AD) is a non-reversible brain disorder that develops over a number of years. At the start of 2014, the number of Americans with AD was estimated... show full transcript
Worked Solution & Example Answer:Alzheimer's disease (AD) is a non-reversible brain disorder that develops over a number of years - AQA - A-Level Biology - Question 10 - 2017 - Paper 2
Step 1
Calculate the annual percentage increase in AD cases in America for 2014
Answer
To calculate the annual percentage increase in AD cases, use the formula:
ext{Percentage Increase} = rac{ ext{New Value} - ext{Old Value}}{ ext{Old Value}} imes 100Here, the New Value is 5.4 million, and the Old Value can be assumed from a previous year. If we assume there were about 5.3 million AD cases in 2013:
ext{Percentage Increase} = rac{5.4 - 5.3}{5.3} imes 100 = 1.89\%Step 2
Explain how donepezil could improve communication between nerve cells
Answer
Donepezil works by inhibiting the enzyme acetylcholinesterase, which breaks down acetylcholine in the synaptic cleft. By preventing the breakdown of acetylcholine, donepezil increases its availability in the synapse, allowing for enhanced communication between nerve cells. This leads to improved signaling and function, particularly in aspects related to memory and cognition, which are impaired in AD.
Step 3
Suggest and explain two reasons why there is a high frequency of the E280A mutation in Yaramul
Answer
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Founder Effect: The small, isolated population of Yaramul likely descended from a few individuals who carried the E280A mutation. As a result, this mutation became more prevalent due to the limited gene pool and high rates of inbreeding.
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Inheritance Patterns: Since the E280A mutation is autosomal dominant, it can be easily passed down to offspring. The hereditary nature of this mutation means that it remains present and can accumulate in the population over generations.
Step 4
Explain why natural selection has not reduced the frequency of the E280A mutation in the population
Answer
Natural selection may not have reduced the frequency of the E280A mutation because individuals carrying the mutation can reproduce before the symptoms of AD develop. Since symptoms typically manifest later in life, those affected may have already contributed to the gene pool, allowing the mutation to persist.
Step 5
Suggest and explain one reason for the variation in age of E280A mutation expression causing AD
Answer
One reason for the variation in age of expression could be epigenetic factors, such as environmental influences or lifestyle choices that can affect gene expression. Factors such as diet, stress, and exposure to toxins can alter the epigenome, leading to differences in how and when the mutation manifests as AD.
Step 6
Suggest explanations for the figures the scientists recorded
Answer
The discrepancy between the number of detected E280A mutations and the potential AD cases can be attributed to several factors:
- Incomplete Penetrance: Not all individuals with the E280A mutation will develop AD, indicative of genetic variability.
- Asymptomatic Carriers: Some individuals may carry the mutation without showing symptoms, which might result in fewer diagnosed cases relative to the mutations detected.
Step 7
Suggest why a DNA probe for the mutated triplet was not considered a suitable method for detection of the E280A mutation
Answer
The DNA probe might not be suitable because it could bind to other similar sequences within the genome, leading to non-specific binding. This would produce false positives and make it challenging to accurately identify the presence of the E280A mutation.