This genotype may be the ancestor of the other genotypes. Phenotypic patterns are variant to possible expressions from paternal and maternal genotypes. Flowers of heterozygous plants have a phenotype somewhere between the two homozygous genotypes. These genes make up different DNA sequences called genotypes. Some degree of gene flow is normal, and preserves constellations of genes and genotypes. Three genotypes (with subtypes) have been recognised. Despite the variety of measles genotypes, there is only one measles serotype. The prevalence of coeliac disease genotypes in the modern population is not completely understood. B. Clade A has five genotypes and clade B has one. Laboratory mice have been infected successfully with a variety of avian flu genotypes. Isogenic organisms have identical, or near identical genotypes. These two genotypes may be separate species. Differences in fitness between genotypes predict the rate of evolution by natural selection. There are four known "Dobrava" virus genotypes, each carried by a different rodent species. A single lichen may contain several algal genotypes.