The pedigree shows the inheritance of a trait controlled by a pair of alleles - HSC - SSCE Biology - Question 17 - 2011 - Paper 1
Question 17
The pedigree shows the inheritance of a trait controlled by a pair of alleles.
Key
⬤ Phenotype 1
⬤ Phenotype 2
⬤ Phenotype 3
Which Punnett square correctly repres... show full transcript
Worked Solution & Example Answer:The pedigree shows the inheritance of a trait controlled by a pair of alleles - HSC - SSCE Biology - Question 17 - 2011 - Paper 1
Step 1
Identify the Parent Genotypes
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Answer
From the pedigree, the two parents in generation I are phenotypes 1 (represented by the square) and 2 (represented by the circle). We will denote phenotype 1 as genotype AA (homozygous dominant) and phenotype 2 as Aa (heterozygous).
Step 2
Determine the Potential Gametes
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Answer
The potential gametes for each parent can be illustrated as follows:
Parent 1 (AA): can produce gametes A (all offspring will inherit A).
Parent 2 (Aa): can produce gametes A and a.
Step 3
Construct the Punnett Square
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Answer
The Punnett square will have the gametes from Parent 1 along the top and those from Parent 2 along the side:
A A
---------
A | AA | AA |
---------
a | Aa | Aa |
---------
Step 4
Identify the Offspring Phenotypes
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Answer
The resulting genotypes from the Punnett square are AA (phenotype 1) and Aa (phenotype 1). All offspring will display phenotype 1. The cross leads us to conclude that the correct Punnett square is the one labeled as D.
