Many embryo-defective mutants of Arabidopsis have been generated using a short p

Question

Many embryo-defective mutants of Arabidopsis have been generated using a short piece of transferred bacterial DNA (T-DNA) that randomly disrupts the coding region of an EMB gene. Such mutants are said to be “tagged”. Because the T-DNA carries a dominant antibiotic resistance gene, heterozygous plants (EMB/emb) are antibiotic resistant and produce siliques (fruits) with 25% aborted seeds. By contrast, some embryo-defective mutants generated with this procedure are considered “not tagged” because the induced mutation responsible for embryo abortion is unlinked to the T-DNA insertion site (located on a different chromosome). One explanation for the origin of the mutations in these untagged mutants is that the T-DNA causes a small deletion in the EMB gene but later integrates into a different chromosomal region without disrupting an essential gene.

What percentage of seedlings produced from self-pollination of a tagged heterozygote should be antibiotic resistant?

What percentage of resistant plants noted in (a) should produce siliques with 25% aborted seeds?

What percentage of seedlings produced from self-pollination of an untagged heterozygote should be antibiotic resistant?

What percentage of resistant plants noted in (c) should produce siliques with 25% aborted seeds?

Explanation / Answer

Mutations in genes classified as "Embryo Defective" give an embryo-defective phenotype characterized by a morphological defect in seed development. Those classified as "Seed Pigment" result in a defect in seed pigmentation (albino, pale green, fusca) but not in morphogenesis.

With the "50% Defective Seeds" class, siliques produce ~50% mutant seeds following self-pollination of heterozygotes, regardless of pollen genotype.'

Ans1. from above information

25% mutant seeds will be produced from self-pollination of a tagged heterozygote should be antibiotic resistant

These mutants will be antibiotic resistant

Therefore total percentage of seedlings produced from self-pollination of a tagged heterozygote should be antibiotic resistant will be 50%.

2. Resistant plants noted in (1) should produce siliques with 25% aborted seedswill be 25%

3. therefore 50 percent of seedlings produced from self-pollination of an untagged heterozygote should be antibiotic resistant.

4. percentage of resistant plants noted in (3) should produce siliques with 25% aborted seeds will be 25%.

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