The genes for pod shape and colour assort independently - VCE - SSCE Biology - Question 33 - 2015 - Paper 1
Question 33
The genes for pod shape and colour assort independently. A cross was performed between two plants that are heterozygous for both pod shape and colour. The ratio of p... show full transcript
Worked Solution & Example Answer:The genes for pod shape and colour assort independently - VCE - SSCE Biology - Question 33 - 2015 - Paper 1
Step 1
Determine the Parental Genotypes
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Answer
Both parent plants are heterozygous for pod shape and colour. Let 'I' represent the allele for inflated pods and 'i' for constricted pods. For colour, let 'Y' represent yellow and 'y' represent green. Thus, both parents have the genotype 'IiYy'.
Step 2
Set Up the Punnett Square
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Answer
To find the offspring ratios, create a 4x4 Punnett square to account for all combinations of alleles:
Possible gametes from each parent are: 'IY', 'Iy', 'iY', 'iy'.
Fill in the Punnett square:
Step 3
Fill in the Punnett Square
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Answer
The resulting genotypes will be:
IY
Iy
iY
iy
IY
IIYY
IIYy
IiYY
IiYy
Iy
IIYy
IIyy
IiYy
Iiyy
iY
IiYY
IiYy
iiYY
iiYy
iy
IiYy
Iiyy
iiYy
iiyy
From this, we analyze the phenotypic outcomes.
Step 4
Count the Phenotypes
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Answer
From the completed Punnett square, we find the phenotypes:
9 Inflated Green (I_Y_)
3 Inflated Yellow (I_yy)
3 Constricted Green (iiY_)
1 Constricted Yellow (iiyy)
Thus, the resultant phenotypic ratio will be 9:3:3:1.
Step 5
Choose the Correct Ratio
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Answer
By comparing the resultant ratio with the options provided, the correct answer is (C): 9 inflated, green : 3 constricted, green : 3 inflated, yellow : 1 constricted, yellow.
