A polymorphism is a genetic variant. The term is usually limited to variants that are moderately common (i.e., it is unusual for the term to be used when referring to rare variants).
Moderately common genetic variants tend to have modest effects on traits; therefore, the variance explained in that trait by common polymorphisms (including single nucleotide polymorphisms (SNPs)) is usually relatively small. Thus, MR studies using moderately common polymorphisms will require large sample sizes or the combination of many polymorphisms (e.g., within a polygenic risk score (PRS)) for adequate statistical power.
References
Other terms in 'Useful genetic terms ':
- Allele
- Chromosome
- Cis- and trans-variants
- Copy number variation
- Deoxyribonucleic acid (DNA)
- Gene
- Genetic variant
- Genotype
- Haplotype
- Heterozygous or Heterozygote
- Homozygous or Homozygote
- Linkage disequilibrium (LD)
- Locus
- Palindromic single nucleotide polymorphism (SNP)
- Polygenic risk score (PRS)
- Rare variants
- Single nucleotide polymorphism (SNP)