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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 for the F₂ generation from a cross of homozygous green pods (GG) and homozygous yellow pods (gg) would be:
- Homozygous green (GG)
- Heterozygous (Gg)
- Homozygous yellow (gg)
Since the F₁ generation consists of all heterozygous (Gg) individuals, the F₂ generation will include a mix of these genotypes in a typical Mendelian ratio.
Step 2
Using your understanding of current genetic thinking, interpret the results of the F₂ cross depicted above.
Answer
In the F₂ generation, the ratio of green to yellow pods can be interpreted as follows:
The ratio of green to yellow pods is approximately 3:1, as seen in the numbers provided (1560 green: 482 yellow). This supports Mendelian genetics, where the dominant allele (G) results in green pods, while the recessive allele (g) results in yellow pods.
The presence of a 3:1 ratio implies that the F₂ generation resulted from a monohybrid cross, leading to the expression of the dominant phenotype (green) in three-fourths of the offspring. This aligns with the principles of segregation and independent assortment, showcasing how traits are inherited.
Step 3
Describe the features of TWO experimental techniques used by Mendel that led to his success.
Answer
Mendel employed several experimental techniques which were fundamental to his success in understanding inheritance:
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Controlled Cross-Pollination: Mendel carefully controlled which plants he cross-pollinated to ensure that he could study specific trait inheritance. He removed the anthers from flowers to prevent self-pollination, allowing for accurate tracking of parental traits.
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Large Sample Sizes: Mendel analyzed a large number of pea plants across multiple generations. This robust sample size allowed him to derive meaningful statistical conclusions from the offspring ratios, leading to the formulation of his laws of inheritance.