Polymorphic Trait and Monomorphic Trait

Polymorphic Trait and Monomorphic Trait

Polymorphic Trait

According to the (Larsen, 2014), a polymorphic trait is a trait that results from the availability of alternative forms of DNA nucleotide or genes at a particular locus and which their occurrence is higher than 1% of their population.

Examples of polymorphic traits include Blood group, skin color for they result from interactions from the different genes of both parents

Monomorphic Trait

They are traits that are a representation of one a set of visible features of an individual as a result of the genetic configuration, or merely genotype in the population.  It is also a trait resulting from a fixed allele in that all the individuals of a population exhibit the same set of visible features.

Examples of a monomorphic trait are bipedalism or walking on double legs.

Balanced Polymorphism

As described by (Larsen, 2014), a balanced polymorphism is an occurrence that tends to maintain different phenotypes in almost stable presence in a population.

As a perfect example of a balanced polymorphism, sickle cell anemia occurs due to the changes in the molecular structure of its hemoglobin. During the changes in the same hemoglobin structure, some of the blood cells might become weak and hence would deprive their ability to carry oxygen in the body. In the heterozygous state, there is a chance of the occurrence of both normal red blood cells as well as the sickle cells, and both carry oxygen depending on their ability to transport.


Directional Selection

Directional selection is experienced when there is a selection of one allele exceeding the other alleles selection, and that results in the formation of the occurrence or frequencies to transpose in one direction.

A perfect example of a directional selection is the frequencies of the peppered moth. In the early 19th century in England, there were two species of moths before the industrial revolution, the dark gray moth and the light gray moth. The occurrence of the light gray moth s exceeded the frequency of the dark gray moths. As mining of coal intensified in England, the production of soot also increased, especially in the atmosphere and at the bark of trees. Because the moths were mostly populated in the trees, the light gray moths became easy prey for predators for they would be visible in a dark object than the dark gray moths. The reduction of the light gray moths also meant the decline of their offsprings, thus leading to more populace within the black gray moths (Larsen, 2014).


Larsen, C. S. (2014). Our Origins: Discovering Physical Anthropology. New York: W. W. Norton & Company.



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