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.
In some fam... show full transcript
Worked Solution & Example Answer:This question is about inheritance - AQA - GCSE Biology Combined Science - Question 5 - 2020 - Paper 2
Step 1
Complete Figure 5.
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Answer
| Female | |
| X | X |
|---------|-------|
| Male | |
| Y | XY |
Step 2
In some families all children are the same sex.
Give the reason why.
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Answer
There is a 50% chance of each child being male or female, depending on whether the sperm fertilizing the egg carries an X or Y chromosome. Therefore, it is possible for all children to be the same sex.
Step 3
Draw a Punnett square diagram to find the probability that their next child will have CF.
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| | T | t |
|-------|-------|-------|
| T | TT | Tt |
|-------|-------|-------|
| t | Tt | tt |
In this Punnett square, TT represents children without CF, Tt are carriers, and tt shows the child with CF. The probability that their next child will have CF (tt) is thus 1 in 4, or 25%.
Step 4
Suggest three reasons for choosing Method 1 instead of Method 2.
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Method 1 does not involve invasive procedures like IVF, reducing stress for the woman.
Higher chances of successful pregnancy as the risk of miscarriage is lower compared to IVF.
The test in Method 1 is freely available and can be done without waiting for IVF.
Step 5
Suggest one advantage of Method 2.
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One advantage of Method 2 is that it allows the couple to ensure that only embryos without CF are implanted, reducing the chance of miscarriage and providing them a better chance of having a healthy baby.
