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This question is about inheritance - AQA - GCSE Biology Combined Science - Question 5 - 2020 - Paper 2
Question 5
This question is about inheritance. Humans have 23 pairs of chromosomes in each body cell. One pair of chromosomes determines sex. Complete Figure 5. Figure 5 ... show full transcript
Worked Solution & Example Answer:This question is about inheritance - AQA - GCSE Biology Combined Science - Question 5 - 2020 - Paper 2
Step 1
Step 2
In some families all children are the same sex. Give the reason why.
Answer
In some families, all children can be the same sex due to the random nature of which sperm cells (carrying either X or Y chromosomes) fertilize the egg. Each child has a 50% chance of being male or female, but it's possible, by chance, for all children to be of the same sex.
Step 3
Draw a Punnett square diagram to find the probability that their next child will have CF.
Answer
The Punnett square for the scenario where both parents are carriers (Tt) is as follows:
T t
___________________
T | TT | Tt
---------------------
T | Tt | tt
In this case, TT = normal, Tt = carrier, and tt = affected by CF. The probabilities are:
- TT: 25%
- Tt: 50%
- tt: 25%
Thus, the probability of the next child having CF (tt) is 25%.
Step 4
Suggest three reasons for choosing Method 1 instead of Method 2.
Answer
- Does not need IVF which is stressful/invasive.
- Higher chance of successful pregnancy as risk of miscarriage is low compared to the 30% success rate of IVF.
- The test is freely available and can be carried out even if the mother is pregnant.
Step 5