Allele, genotype and phenotype

An allele is a particular variant of a gene. Because chromosomes come in pairs, you carry two alleles per gene; together they form the genotype. If both are equal you are homozygous, if they differ heterozygous. The phenotype is the observable trait that arises from genotype and environment.

ALLELE · GENOTYPE · PHENOTYPE combine show as Two allelesGenotypePhenotype C from the mother T from the father C / T heterozygous visible trait genotype + environment Equal alleles are homozygous (C/C), different ones heterozygous (C/T). Genome names the genotype; whether it shows depends on dominance and environment.

Allele and genotype

At a position different text can stand, say C or T. Each of these versions is an allele. Since you have two copies of every autosome, one from the mother, one from the father, you always carry two alleles. Their combination is the genotype: C/C and T/T are homozygous, C/T is heterozygous.

From genotype to phenotype

The phenotype is what you ultimately see or measure, from eye colour to a lab value. It does not follow one to one from the genotype. Environment, lifestyle, chance and the interplay of many genes shift the picture. The same genotype can turn out differently in two people.

How Genome presents this

Genome shows the technical genotype at a position, that is which two alleles you carry. What this genotype means is given in the respective article and depends on whether an allele acts dominantly or recessively and how fully it prevails. The genotype is the starting point of interpretation, not its end.

What Genome measures. Genome reports the genotype at a position, for example C/T. Whether that becomes a visible trait depends on dominance, environment and other genes.

Related topics

Chromosomes and karyotypeDominant and recessiversIDs, microarray and SNP lookupPenetrance and expressivityMutation and variant

Sources

  1. 1Johannsen, 1911 The genotype conception of heredity. The American Naturalist 45:129–159. doi.org/10.1086/279202
  2. 2Hardy, 1908 Mendelian proportions in a mixed population. Science 28:49–50. doi.org/10.1126/science.28.706.49