A student amplifies a portion of the human ALDH2 gene by PCR from cheek-cell DNA of three siblings (A, B, C) and the products are loaded into a 1% agarose gel along with a 100-bp ladder. After electrophoresis at 100 V for 30 min, the gel is stained and photographed.
Which sibling appears heterozygous for a length polymorphism at this locus?
- A
C (one band at 200 bp)
- B
A (one band at 400 bp)
- C
None of the siblings
- Dcheck_circle
B (two bands)
Explanation
Sibling B shows two bands (about 400 and 200 bp), indicating two alleles of different size at this locus. A and C each show a single band, consistent with homozygosity.