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A plant breeder replicated one of Mendel’s pea plant breeding experiments - HSC - SSCE Biology - Question 17 - 2004 - Paper 1
Question 17
A plant breeder replicated one of Mendel’s pea plant breeding experiments. The results of the cross between green (G) pods and yellow (g) pods are shown in the table... show full transcript
Worked Solution & Example Answer:A plant breeder replicated one of Mendel’s pea plant breeding experiments - HSC - SSCE Biology - Question 17 - 2004 - Paper 1
Step 1
List all possible genotypes of the F₂ generation.
Answer
The possible genotypes of the F₂ generation, resulting from a cross between homozygous dominant green pods (GG) and homozygous recessive yellow pods (gg) in the F₁ generation, can be represented as follows:
- Homozygous Dominant: GG
- Heterozygous: Gg
- Homozygous Recessive: gg
Thus, the possible genotypes are GG, Gg, and gg.
Step 2
Using your understanding of current genetic thinking, interpret the results of the F₂ cross depicted above.
Answer
The F₂ generation shows a total of 1560 green pods and 482 yellow pods. The expected phenotypic ratio for a monohybrid cross such as this is 3:1, which agrees with the observed data. The green phenotype is dominant over the yellow phenotype.
To analyze this:
- Total pods = 1560 + 482 = 2042
- Expected green pods = (3/4) * 2042 = 1531.5 (approximately 1532)
- Expected yellow pods = (1/4) * 2042 = 510.5 (approximately 511)
The observed values (1560 and 482) align closely with the expected ratios, supporting Mendel's principles of inheritance.
Step 3
Describe the features of TWO experimental techniques used by Mendel that led to his success.
Answer
Mendel employed several techniques that contributed to his success in genetics:
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Controlled Cross-Pollination: Mendel carefully controlled the breeding of his plants by removing the male parts from flowers and manually pollinating them with pollen from other plants. This allowed him to ensure accurate mating between specific pea plant varieties.
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Use of Purebred Lines: He started his experiments with purebred plants to establish clear parental traits and ensure consistent offspring. By using these purebred lines, he could observe and record inheritance patterns more effectively, setting a foundation for his genetic theories.