A dominant trait is not always the more common trait because the frequency of alleles in a population is influenced by factors such as mutation rates, genetic drift, migration, and natural selection. Even if a trait is dominant, if the allele for that trait is rare in the population, the dominant phenotype may also be rare.
For example, if a dominant allele for a trait exists but is present in only a small fraction of the population, the recessive phenotype (which is governed by the recessive allele) may be more common even if the dominant trait is expressed when the dominant allele is present. This can happen with traits influenced by single genes, where the dominant trait can become rarer due to the low frequency of the dominant allele, while the recessive trait has a higher frequency of expression because it is associated with a more common recessive allele.
In summary, the occurrence and visibility of traits in a population depend not just on their dominance or recessiveness, but also on the prevalences of their corresponding alleles.
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