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Two genes and their alleles in tomatoes are shown below - VCE - SSCE Biology - Question 10 - 2005 - Paper 1
Question 10
Two genes and their alleles in tomatoes are shown below. Plant height D tall Fruit shape P spherical d dwarf p pear-shaped These genes are linked. A hetero... show full transcript
Worked Solution & Example Answer:Two genes and their alleles in tomatoes are shown below - VCE - SSCE Biology - Question 10 - 2005 - Paper 1
Step 1
The genotype of the heterozygous parent must be
Answer
To determine the genotype of the heterozygous parent, we analyze the offspring phenotypes and their ratios.
From the data provided:
- Tall spherical: 10
- Tall pear-shaped: 40
- Dwarf spherical: 40
- Dwarf pear-shaped: 10
We can see the following results:
- Total offspring: 100
Phenotypic Ratios
To find the expected ratios for the linked genes, we need to classify the phenotypes.
- The tall plants must have at least one dominant allele (D), while the dwarf plants can only have the homozygous recessive phenotype (dd).
- The spherical fruit must have at least one dominant allele (P), while the pear-shaped fruit must have the homozygous recessive phenotype (pp).
Recessive Gene Analysis
Since we have both dwarf and pear-shaped fruits appearing in the offspring, we conclude that the heterozygous parent must be able to contribute both dominant and recessive alleles.
Conclusion
Given that 40 of the offspring are tall pear-shaped and 40 are dwarf spherical, the heterozygous parent must carry the alleles DP (dominant for height and shape), leading us to conclude that the genotype is:
Answer: B. dp