William Bateson and Reginald Punnett used the sweet pea (Lathyrus odoratus) in geneticsstudies in the early 20 th century. Pure-breeding plants that produced purple flowers and long pollengrains were crossed with pure-breeding plants that produced red flowers and round pollen grains.The resulting offspring all produced purple flowers and long pollen grains. Two of the F 1 generationplants were crossed. The table shows the ratio of phenotypes in the F2 generation.Flower colour Pollen grain shape Number of plantspurple long 4831purple round 390red long 393red round 1138What is an explanation for these experimental results?A. Purple flowers and long pollen grains are dominant and the alleles have assortedindependently.B. The genes for flower colour and pollen shape are linked and all plants producinglong pollen grains are recombinants.C. The genes for flower colour and pollen shape are linked and all plants producingred flowers are recombinants.D. Plants producing purple flowers and round pollen grains arose through crossing over.
Question
William Bateson and Reginald Punnett used the sweet pea (Lathyrus odoratus) in geneticsstudies in the early 20 th century. Pure-breeding plants that produced purple flowers and long pollengrains were crossed with pure-breeding plants that produced red flowers and round pollen grains.The resulting offspring all produced purple flowers and long pollen grains. Two of the F 1 generationplants were crossed. The table shows the ratio of phenotypes in the F2 generation.Flower colour Pollen grain shape Number of plantspurple long 4831purple round 390red long 393red round 1138What is an explanation for these experimental results?A. Purple flowers and long pollen grains are dominant and the alleles have assortedindependently.B. The genes for flower colour and pollen shape are linked and all plants producinglong pollen grains are recombinants.C. The genes for flower colour and pollen shape are linked and all plants producingred flowers are recombinants.D. Plants producing purple flowers and round pollen grains arose through crossing over.
Solution
The experimental results can be explained by option C: The genes for flower colour and pollen shape are linked and all plants producing red flowers are recombinants.
Here's why:
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The F1 generation all produced purple flowers and long pollen grains, indicating that these traits are dominant.
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In the F2 generation, the most common phenotype was purple flowers with long pollen grains, which is expected if these traits are dominant.
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However, there were also significant numbers of plants with purple flowers and round pollen grains, and red flowers with long pollen grains. This suggests that the genes for flower colour and pollen shape are linked, meaning they are located close together on the same chromosome and tend to be inherited together.
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The presence of plants with red flowers in the F2 generation indicates that recombination has occurred. Recombination is a process during meiosis where sections of DNA are exchanged between homologous chromosomes, creating new combinations of genes.
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The fact that all plants producing red flowers are recombinants suggests that the red flower allele is located on the same chromosome as the long pollen grain allele, and these alleles have been separated through recombination.
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The presence of plants with purple flowers and round pollen grains could also be explained by recombination, but this is less likely given the lower numbers of these plants.
Therefore, the most likely explanation for these results is that the genes for flower colour and pollen shape are linked, and all plants producing red flowers are recombinants.
Similar Questions
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