Q26 - Transgenic Male Sterility and Herbicide Resistance

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Mendel's Laws & Probability in Genetics Recombinant DNA & Biotechnology Techniques

The question involves two transgenic plant lines, P1 and P2, that produce bisexual flowers.

P1 is transformed with a barnase gene linked to a gene (HR) conferring resistance to a herbicide. Expression of the Barnase protein in this plant inhibits pollen formation, making the plant unable to produce fertile pollen. Male sterility and herbicide resistance are both dominant characters.

P2 is transformed with a barstar gene, also linked to the HR gene. In the presence of Barstar protein, the activity of Barnase protein is inhibited, restoring pollen formation. The activity of the Barstar protein is a dominant character.

In P1, the barnase gene lies in linkage group 2, whilst in P2, the barstar gene is in linkage group 3.

P1 is hemizygous for the barnase and HR genes. P2 is homozygous for both the barstar and HR genes.

A cross is made between P1 and P2. The F1 progeny are self-pollinated and the F2 progeny are analyzed.

Q26.1. What percentage of F1 progeny will be unable to produce fertile pollen?

Q26.2. What percentage of F1 progeny will be herbicide resistant?

Q26.3. What percentage of F2 progeny will be unable to produce fertile pollen? Give your answer to the nearest whole number.

Q26.4. What percentage of F2 progeny will be herbicide resistant? Give your answer to the nearest whole number.

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Question reproduced from IBO 2023, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF