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Retinitis pigmentosa is a genetic condition that affects the eyes - OCR Gateway - GCSE Biology - Question 18 - 2018 - Paper 4
Question 18
Retinitis pigmentosa is a genetic condition that affects the eyes. It is caused by a mutation to a gene. This mutation produces a recessive allele. The condition cau... show full transcript
Worked Solution & Example Answer:Retinitis pigmentosa is a genetic condition that affects the eyes - OCR Gateway - GCSE Biology - Question 18 - 2018 - Paper 4
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(i) Draw a genetic diagram to calculate the probability that the baby will have the condition.
Answer
To determine the probability that the baby will have retinitis pigmentosa, we can use a Punnett square.
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Set up the Punnett square:
- Parent 1 gametes: R (normal allele) and r (allele for retinitis pigmentosa)
- Parent 2 gametes: R (normal allele) and r (allele for retinitis pigmentosa)
R r R RR Rr r Rr rr -
Identify the genotypes of the offspring:
- RR (homozygous normal): 1
- Rr (heterozygous): 2
- rr (homozygous affected): 1
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Calculate the probabilities:
- Probability of RR = 1/4 or 25%
- Probability of Rr = 2/4 or 50%
- Probability of rr = 1/4 or 25%
Thus, the probability that the baby will have retinitis pigmentosa (genotype rr) is 25%.