Q27 — PCR Mapping of Genomic Rearrangements in Genes H and K

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

Chromosomal Variation: Number & Structure

It is known that human genes H (located on chromosome 1) and K (located on chromosome 5), are highly prone to genomic rearrangements, such as deletions, translocations, duplications, and inversions. From a given population, three individuals (ID-1, ID-2, and ID-3) are known to have genomic rearrangements at these loci. Polymerase Chain Reaction (PCR) was performed to determine the type of rearrangement. Primers for PCR were indicated as small arrows in Figure 1A (the arrowhead denotes the 3’ end of the primer).

Panel A: exon/intron diagrams of genes H and K with primers a,b on H and c,d,e on K. Panel B: a wild-type PCR gel with 5 primer-pair lanes, only c+e and a+b giving bands. Panel C: PCR gels for ID-1, ID-2, and ID-3 across the same 5 primer pairs, each showing a different band pattern from wild-type. Figure 1. A. The structure of genes K and H, where black regions depict exons, while light gray regions are introns. Note that for both genes, the junction between depicted exons codes for an active site in their respective protein (enzyme) products. B. PCR results from a wild-type (WT) individual (M - DNA size marker). C. PCR results from three tested individuals (ID-1, ID-2, and ID-3). Note that the intensity of the bands does not represent the amount of DNA.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. In ID-1, there is a translocation event between chromosomes 1 and 5.

B. ID-2 has an inversion, resulting in a non-functional protein product.

C. ID-3 has a deletion.

D. ID-1 is homozygous for the rearrangement, while ID-3 is heterozygous.

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