Characteristics of genetic markers: Codominance of alleles

Codominant markers are markers for which both alleles are expressed when co-occurring in an individual. Therefore, with codominant markers, heterozygotes can be distinguished from homozygotes, allowing the determination of genotypes and allele frequencies at loci. In contrast, band profiles of dominant markers are scored as the presence or absence of fragments of a particular size, and heterozygosity cannot be determined directly. As a consequence, only an approximation of allele frequency can be obtained by assuming Hardy-Weinberg equilibrium in a population and estimating allele frequency from the proportion of individuals with the absent phenotype (homozygous recessive). For predominantly self-fertilizing species, heterozygosity could be disregarded and allele frequencies be considered equal to observed band frequencies. Codominant markers are preferred for most applications. The majority of codominant markers are single locus markers and hence the degree of information per assay is usually lower compared to the multilocus techniques.