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Experiments were conducted to obtain data on the traits ‘seed shape’ in plants and ‘feather colour’ in chickens - HSC - SSCE Biology - Question 30 - 2019 - Paper 1
Question 30
Experiments were conducted to obtain data on the traits ‘seed shape’ in plants and ‘feather colour’ in chickens. In each case, the original parents were pure breedin... show full transcript
Worked Solution & Example Answer:Experiments were conducted to obtain data on the traits ‘seed shape’ in plants and ‘feather colour’ in chickens - HSC - SSCE Biology - Question 30 - 2019 - Paper 1
Step 1
Explain the phenotypic ratios of the F2 generation in both the plant and chicken breeding experiments.
Answer
Graph A shows a phenotypic ratio of 3:1 in the F2 generation. The pure breeding parents must have been homozygous for round seed shape (RR) and wrinkled (rr). The resulting F1 generation is heterozygous (Rr) and when self-pollinated will produce the following Punnett square:
| | R | R |
|---|---|---|
| r | Rr | Rr |
| r | Rr | Rr |
This leads to a ratio of 3 round seeds to 1 wrinkled seed.
Graph B demonstrates a phenotypic ratio of 1:2:1 for feather color, indicating co-dominance. Here, the black feather allele (B) co-exists with the white feather allele (W). In the F1 generation, the chickens express both alleles and are heterozygous (BW). The Punnett square is:
| | B | W |
|---|---|---|
| B | BB | BW |
| W | BW | WW |
This results in 50% with black feathers (BB), 25% with black and white feathers (BW), and 25% with white feathers (WW), summarizing the 1:2:1 ratio.