Q41 - Backcrossing to Introgress a Disease-Resistance Allele

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

Quantitative Genetics, Heritability & Inbreeding

A plant crop is susceptible to leaf rust. In a screening of old varieties from a gene bank, a resistance allele B was discovered. In an intensive backcrossing program, this allele was introgressed to the crop (Fig.). Resistance was tested in each generation.

Intensive breeding program. D is donor of a dominant resistance allele B, and b is the allele in the standard crop plant being susceptible to rust. S is the variety into which gene B is introduced

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. 93.75% of the alleles, not linked to allele B, in D3 come from S

B. At least 10 backcrossings are needed to get the percentage of D genes below 1%

C. More crosses are needed to introgress a recessive resistance allele than a dominant one

D. Introgression cannot be done with quantitative traits

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Question reproduced from IBO 2015, Theoretical Exam B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)