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Diagram W shows part of a metabolic pathway involving the amino acids phenylalanine and tyrosine - VCE - SSCE Biology - Question 2 - 2009 - Paper 1
Question 2
Diagram W shows part of a metabolic pathway involving the amino acids phenylalanine and tyrosine. One or more enzymes are involved at each step in such a pathway. T... show full transcript
Worked Solution & Example Answer:Diagram W shows part of a metabolic pathway involving the amino acids phenylalanine and tyrosine - VCE - SSCE Biology - Question 2 - 2009 - Paper 1
Step 1
With reference to these two genes, what is the chance that Emily has the same genotype as her parents?
Answer
The couple is heterozygous for both genes (Pp and Aa). Therefore, they can produce the following combinations of alleles for Emily:
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From gene P:
- P from one parent and P from the other results in a genotype of PP
- P from one parent and p from the other results in a genotype of Pp
- p from one parent and A from the other results in a genotype of pp
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From gene A:
- A from one parent and A from the other results in a genotype of AA
- A from one parent and a from the other results in a genotype of Aa
- a from one parent and a from the other results in a genotype of aa
The combinations would yield:
- PP AA
- PP Aa
- Pp AA
- Pp Aa
- Pp aa
- pp AA
- pp Aa
- pp aa
To find the chance Emily has the same genotype as her parents (assuming both parents have the genotype Pp Aa), we look for the combination (Pp Aa). The possible combinations are 4 out of 8, making the chance 50%.
Step 2
Are Jack and Tom identical twins or non-identical twins? Explain.
Answer
Jack and Tom have different genotypes: Jack is Pp aa, while Tom is PP Aa. Since identical twins arise from the same fertilized egg and share the same genetic material, and Jack and Tom have different alleles for both genes, they cannot be identical twins. Therefore, Jack and Tom are non-identical twins because they stem from two separate eggs fertilized by two separate sperm.