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 2
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.
1.
2.
In tom... 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 2
Step 1
Suggest two reasons why.
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Answer
Small sample size may lead to non-representative results.
Fusion/fertilisation of gametes is random.
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 ttmm.
Step 3
Use the information provided to explain the results in Table 3.
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Answer
The results indicate that the genes are linked, as the expected ratios from independent assortment do not match. This suggests that the traits are inherited together more often than not.
There are fewer tall plants with mottled leaves and dwarf plants with normal leaves than expected, indicating the influence of linked genes.
The occurrence of crossing over could produce some recombination of traits, leading to a smaller number of the rarer combinations observed in the table.
Step 4
Complete Table 4 to show the expected ratio of phenotypes.
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Answer
Here's the expected phenotype ratio if the genes are on different homologous pairs:
