The number of different genotypes that would be expected in the offspring of a cross between plant 1 and plant 2 is
A - VCE - SSCE Biology - Question 29 - 2014 - Paper 1
Question 29
The number of different genotypes that would be expected in the offspring of a cross between plant 1 and plant 2 is
A. 2
B. 4
C. 6
D. 8
Worked Solution & Example Answer:The number of different genotypes that would be expected in the offspring of a cross between plant 1 and plant 2 is
A - VCE - SSCE Biology - Question 29 - 2014 - Paper 1
Step 1
Determine the Genotypes of Plants 1 and 2
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Answer
Plant 1 is tall (T) with a black stem (B). Assuming T is dominant over dwarf (t) and B is dominant over red (b), the potential genotype for Plant 1 can be TTBb or TtBb. Plant 2 has a dwarf (t) and a red stem (bb), making its genotype ttbb.
Step 2
Perform a Punnett Square Analysis
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Answer
Using the possible genotypes of Plant 1 (TTBb or TtBb) crossed with ttbb, we can set up Punnett squares.
For TTBb x ttbb:
TTBb yields 2 TtBb and 2 Ttbb.
Genotypes are TtBb (tall, black) and Ttbb (tall, red).
For TtBb x ttbb:
TtBb yields 4 combinations: TtBb, Ttbb, ttBb, and ttbb.
Genotypes are TtBb (tall, black), Ttbb (tall, red), ttBb (dwarf, black), and ttbb (dwarf, red).
So, either case yields different genotypes.
Step 3
Calculate the Total Number of Genotypes
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Answer
From TTBb x ttbb, we have 2 distinct genotypes. From TtBb x ttbb, we have 4 distinct genotypes. The maximum expected unique genotypes from during the cross of the two plants is 4.
Step 4
Conclude the Answer
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Answer
Based on the analysis, the answer to the question is 4 unique genotypes.
