Which of the following is a STRUCTURAL genomic variation?

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To start, let's identify what counts as a structural genomic variation. Structural variations are large-scale changes in the genome that rearrange the structure of chromosomes, such as extra copies, deletions, duplications, inversions, or translocations that affect significant spans of DNA.

Option 1: 'A 10-base-pair deletion in the HBB gene associated with β-thalassemia' is a small indel (deletion of 10 bases) within a single gene. This is a micro-scale variant, not a structural rearrangement of chromosome architecture. It alters sequence but does not change chromosome number or large segments of chromosomes.

Option 2: 'Short CAG tandem repeat in HTT causing Huntington’s disease' refers to a trinucleotide repeat expansion. While pathogenic, these are typically categorized as microsatellite or repeat-number variants rather than large structural rearrangements of the genome. They are small-scale sequence changes, not structural variations like CNVs or aneuploidies.

Option 3: 'A single-nucleotide polymorphism (SNP) in the TP53 linked to cancer risk' is a single base change. SNPs are the smallest class of genetic variation and do not affect chromosome structure or copy number; thus they are not structural variations.

Option 4: 'A 1-base-pair insertion in the CFTR gene that is implicated in cystic fibrosis' is another micro-indel. Though it can have functional consequences, it does not constitute a structural chromosomal rearrangement or copy-number change at the chromosome level.

Option 5: 'Trisomy 21 — an extra copy of chromosome 21 in Down syndrome' represents aneuploidy, i.e., an altered chromosome number, leading to an extra entire chromosome copy. This is a classic example of a structural genomic variation because it changes the structure and copy number of a chromosome.

In summary, options 1–4 describe small-scale sequence changes (point mutations, small indels, or repeat variations) that alter DNA sequence but not chromosome structure, whereas option 5 describes a whole-chromosome copy-number alteration, which is textbook structural variation. Therefore, the structural genomic variation among the choices is Trisomy 21.

BMI5102 BMI5102 Final Assessment Section - MCQs & SAQs

Which of the following is a STRUCTURAL genomic variation?

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