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In a certain plant species, individual plants have either yellow, red or orange flowers - HSC - SSCE Biology - Question 15 - 2015 - Paper 1
Question 15
In a certain plant species, individual plants have either yellow, red or orange flowers. Two plants, each with a different flower colour, were crossed in a breeding... show full transcript
Worked Solution & Example Answer:In a certain plant species, individual plants have either yellow, red or orange flowers - HSC - SSCE Biology - Question 15 - 2015 - Paper 1
Step 1
What were the genotypes of the original parent plants?
Answer
To determine the genotypes of the original parent plants, we need to analyze the F2 generation results. We have:
- 6 red plants
- 11 orange plants
- 5 yellow plants
Assuming that:
- Red (R) is dominant over Orange (r),
- Yellow (Y) is produced when red and orange are absent.
From the numbers provided, the F2 generation results (6 red, 11 orange, and 5 yellow) show a typical Mendelian ratio of 9:3:4.
Given this, one possible combination of the parent genotypes could be RR (homozygous dominant red) crossed with rr (homozygous recessive orange). This would result in:
- All F1 plants being Rr (red),
- When F1 plants self-fertilize, the resulting ratios in the F2 could produce a mix of red, orange, and yellow, corresponding to phenotype proportions of 9:3:4.
Thus, the genotypes of the original parent plants are RR (red) and rr (orange), which corresponds to option (B).