What is allele dropout and allele dropout risk in low-template samples?

What is allele dropout and allele dropout risk in low-template samples?

• A. The appearance of an extra allele in a profile; caused by contamination.
• B. A situation where both alleles in a homozygous locus are missing.
• C. Failure of one allele in a heterozygote due to insufficient template; risk increases in low-template samples and degraded DNA.
• D. A shift in allele sizing due to instrument calibration.

Answer: (C)

Allele dropout happens when, in a PCR-based profile, one of the two alleles at a heterozygous locus fails to amplify enough to be detected. This is most likely when there isn’t much starting DNA. With low-template samples, the random distribution of a small number of DNA copies means one allele can be underrepresented or completely missed during amplification, so a heterozygous locus may appear homozygous or show only a partial signal. Degraded DNA makes this more likely because fragments may be too short to cover the larger allele’s amplicon, or there aren’t sufficient intact templates for both alleles to amplify, increasing dropout risk. This is different from contamination or a true extra allele, which would create a spurious or mixed signal rather than a missing one, and it’s different from a sizing shift caused by instrument calibration, which affects how alleles are measured rather than whether they are detected.

Allele dropout happens when, in a PCR-based profile, one of the two alleles at a heterozygous locus fails to amplify enough to be detected. This is most likely when there isn’t much starting DNA. With low-template samples, the random distribution of a small number of DNA copies means one allele can be underrepresented or completely missed during amplification, so a heterozygous locus may appear homozygous or show only a partial signal. Degraded DNA makes this more likely because fragments may be too short to cover the larger allele’s amplicon, or there aren’t sufficient intact templates for both alleles to amplify, increasing dropout risk. This is different from contamination or a true extra allele, which would create a spurious or mixed signal rather than a missing one, and it’s different from a sizing shift caused by instrument calibration, which affects how alleles are measured rather than whether they are detected.