You have created a Ti plasmid with a T-DNA containing the left border, an NPT II

Question

You have created a Ti plasmid with a T-DNA containing the left border, an NPT II gene, an opine synthesis gene, and a right border. Among the plants transformed with this T-DNA, you discover one plant in which 25% of its progeny have the phenotype of plastid protein import (ppi) mutants. You designate the mutation as ppi54. Plants homozygous for the mutation die as seedlings. To determine whether the mutation is caused by the insertion of the T-DNA into the PPI54 gene, you do the following experiment: 1) Self pollinate a plant heterozygous for the ppi54 mutation. 2) Grow progeny from this self. 3) Score the plants as being either heterozygous for the ppi54 mutation (HET) or homozygous for the wild type gene (WT). Also determine whether these plant produce opines. The following results are obtained. Assume that there T-DNA has inserted at only one location in each of the transgenic plants. Do these results prove whether or not the ppi54 mutation results from insertion of the T-DNA described above? Explain your answer.

Explanation / Answer

The results prove that ppi54 mutation does not result from insertion of the above described T-DNA. Mutation due to insertion of T-DNA results in opines synthesis in heterozygous plants but not in wild type plants. However the results above show that the wild type plant#4 produces opines. Also, we are assuming that the T-DNA has inserted at only one location in each of the transgenic plants and hence it is not necessary that the T-DNA insertion has taken place into the PPI54 gene in all the transgenic plants. The insertion of the gene could have taken place in other genes also. Because of these reasons a T-DNA containing the opine synthesis gene cannot be causing the mutation.

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