Allele frequency vs MAF
An allele is one version of a DNA position. If a position can have an A or a G, each version is an allele. Allele frequency measures how often one allele appears in a group of people.
Minor allele frequency is the frequency of the less common allele at that position. If one allele appears in 98% of records and the other appears in 2%, the MAF is 2%.
Some variant databases show frequency as a decimal. A value of 0.01 means about 1 in 100 alleles in that dataset carry the variant. A value of 0.0001 means about 1 in 10,000 alleles.
Why a frequency field can be above 50%
A true MAF for a two-allele position should be 50% or lower because it describes the less common allele. If a field labeled MAF is higher than 0.5, check what the database is really reporting. It may be reporting alternate allele frequency, not minor allele frequency.
This happens because genetic data is usually compared with a human reference genome. The reference genome is a coordinate sequence, not a list of the most common alleles in every population. The first public human reference was assembled from a small number of anonymous donors, and much of it came from one donor. A reference allele can therefore be less common than the alternate allele in a population dataset.
For a simple two-allele site, an alternate allele frequency of 0.72 means the other allele is about 0.28 in that dataset. In that case, the minor allele frequency is closer to 0.28, not 0.72. Multi-allelic sites and population-specific frequencies need a closer check.
Why frequency matters
Population frequency gives a reality check. A variant that is very common in healthy population datasets is less likely to cause a severe rare disease by itself. A variant that is very rare may deserve closer review, especially if it changes a protein, affects splicing, or appears in ClinVar.
Frequency is still only one signal. A rare variant can be harmless. A common variant can still matter for traits, medication response, carrier status, or a question that depends on several genes.
What rare does not prove
Rare does not mean pathogenic. A variant can be rare because it has little effect, because it is population-specific, because it is missing from a database, or because the DNA file has a quality problem.
When a variant is rare, check what it changes. A rare intronic variant usually needs different review than a rare stop-gained variant. A rare variant with poor genotype quality should be treated carefully until the call is confirmed.
What common does not rule out
Common does not always mean irrelevant. Some common variants affect enzyme activity, medication handling, nutrient pathways, or trait probability. The question is different: common variants are usually reviewed for context and pattern, not as a single explanation for disease.
For example, a common missense variant may be useful in a pharmacogenomics review. A common variant in a pathway gene may still help explain why a practitioner wants to inspect related genes, labs, and symptoms together.
How Gene Inspector Pro uses frequency
Gene Inspector Pro shows allele frequency beside the rest of the variant evidence. This helps you inspect the reason a variant was highlighted instead of stopping at a summary label.
In a review, check frequency with:
- Variant consequence, such as missense, splice region, stop gained, intron, or regulatory change.
- ClinVar status and the number of supporting submissions.
- Predictor scores such as REVEL, AlphaMissense, and DANN when they apply.
- Genotype quality, source file type, and whether the position came from a SNP array, WGS, or WES file.
- Inheritance marks, notes, and the question being reviewed.
Review checklist
| Step | What to check | Why it matters |
|---|---|---|
| 1 | Frequency value | Shows whether the variant is common, uncommon, rare, or missing from population data. |
| 2 | Consequence | A rare missense or splice variant has a different review path than a rare intronic variant. |
| 3 | ClinVar | Shows whether clinical submissions exist and whether they agree. |
| 4 | Predictor scores | Helps prioritize protein-changing variants, but no score is enough by itself. |
| 5 | File quality | A low-quality genotype can create false confidence. |
| 6 | Review question | The same variant can matter differently in rare disease, pharmacogenomics, carrier screening, or trait review. |
What the DNA file cannot show
A raw DNA file does not show symptoms, lab values, family history, medication response, or whether a variant is causing a condition. It also may miss positions that were not tested by the array or were not called well enough in sequencing data.
Use allele frequency and MAF to decide what deserves closer review. For medical decisions, confirm important findings with an appropriate clinical test and a qualified clinician.
Related review pages
Frequency is most useful when it is connected to other evidence. For variant type context, read what a missense variant is and how splice variants are reviewed. For file-type limits, compare SNP arrays with WGS and WES files.