In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios - AQA - A-Level Biology - Question 6 - 2018 - Paper 1
Question 6
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest two reasons why.
What would be ... show full transcript
Worked Solution & Example Answer:In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios - AQA - A-Level Biology - Question 6 - 2018 - Paper 1
Step 1
Suggest two reasons why the observed phenotypic ratios are not the same as the expected ratios.
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Answer
Genes are linked, which can lead to a reduced variety of gametes and non-random distribution of alleles in the offspring.
Epistasis may occur, where the expression of one gene is affected by another gene, leading to unexpected phenotypic ratios.
Step 2
What would be the genotype of the offspring with dwarf plants and mottled leaves?
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Answer
The genotype of the offspring with dwarf plants and mottled leaves would be represented as 'ttmm' or any arrangement of these alleles.
Step 3
Use the information provided to explain the results in Table 3.
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Answer
The results in Table 3 suggest that the alleles are linked, which results in fewer tall, mottled and dwarf, normal offspring. This indicates that crossing over may have occurred, producing fewer recombinant gametes and leading to a prevalence of the non-recombinant types.
Step 4
Complete Table 4 to show the expected ratio of phenotypes.
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