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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
To determine the chance that Emily has the same genotype as her parents, we first note that both parents are heterozygous for both genes (i.e., Pp Aa).
Using a Punnett square, the possible combinations of alleles from both parents are:
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For gene P:
- P from one parent and P from the other = PP
- P from one parent and p from the other = Pp
- p from one parent and P from the other = Pp
- p from one parent and p from the other = pp
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For gene A:
- A from one parent and A from the other = AA
- A from one parent and a from the other = Aa
- a from one parent and A from the other = Aa
- a from one parent and a from the other = aa
The genotypes of the possible offspring are:
- PPAa, PpAA, PpAa, PPaa, Ppaa, ppAa, PpAA, ppaa.
In this case, the chance of Emily having the same genotype as either parent (Pp Aa) is based on the outcomes from the Punnett square. Since there is only one combination, we have a probability of 1 out of 16, or:
P( ext{Emily is } PpAa) = rac{1}{16}.
Step 2
Are Jack and Tom identical twins or non-identical twins? Explain.
Answer
Jack and Tom are non-identical twins (fraternal twins). This is inferred from their genotypes:
- Jack's genotype is Pp aa, indicating he has one working allele for the P gene but none for the A gene.
- Tom's genotype is PP Aa, indicating he has two working alleles for the P gene and one working allele for the A gene.
Since they have different genotypes, this indicates they developed from two separate eggs fertilized by two separate sperm cells. Identical twins, on the other hand, come from a single fertilized egg that splits to form two embryos, leading to identical genotypes. Therefore, Jack and Tom cannot be identical twins.