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Sickle cell disease is a recessive genetic disorder in humans - Edexcel - GCSE Biology Combined Science - Question 2 - 2021 - Paper 1
Question 2
Sickle cell disease is a recessive genetic disorder in humans. (i) Two parents are heterozygous for sickle cell disease. Complete the Punnett square to show the po... show full transcript
Worked Solution & Example Answer:Sickle cell disease is a recessive genetic disorder in humans - Edexcel - GCSE Biology Combined Science - Question 2 - 2021 - Paper 1
Step 1
Complete the Punnett square to show the possible genotypes of their children.
Answer
The Punnett square for the heterozygous parents Dd can be completed as follows:
D d
---------
D | DD | Dd |
---------
d | Dd | dd |
This shows that the possible genotypes for their children are DD, Dd, and dd.
Step 2
State the percentage probability that their children could have sickle cell disease.
Answer
The percentage probability that their children could have sickle cell disease (genotype dd) is 25%. This is because only one out of the four squares in the Punnett square represents the homozygous recessive genotype (dd).
Step 3
Explain why none of their children will have sickle cell disease.
Answer
None of their children will have sickle cell disease because the father has the genotype dd, which means he carries two recessive alleles. The mother, with the genotype DD, carries two dominant alleles. Therefore, all children will inherit at least one dominant allele from the mother (D), resulting in the genotype Dd, which is heterozygous and does not express sickle cell disease.
Step 4
Describe how these types of cattle could be selectively bred to produce cattle that can survive high temperatures and have good meat quality.
Answer
To produce cattle that can survive high temperatures and have good meat quality, one could:
- Cross breed Brahman cattle (which survive well in high temperatures) with Shorthorn cattle (which have good meat quality).
- Select the offspring that exhibit both traits (survival and meat quality).
- Repeat this process over many generations to enhance these traits in the resulting cattle.
Step 5
Give two benefits of breeding wheat plants that are resistant to fungal disease.
Answer
- Wheat plants that are resistant to fungal disease would not be damaged, ensuring a higher yield.
- The spread of the fungus will be reduced, leading to less crop loss and potentially lower costs on fungicides or pesticides.