Blending Inheritance

In the era before the Socratic era, philosophers of the time considered pangenesis as the primary theory of explaining inheritance. The observation that certain traits such as height appeared in children as an average of their parents’ height gave rise to the blending theory. Accordingly, every part of the human body generated a gemmule which later collectively merged in the male semen and led to the formation of the next organism (Hippokrates, pp 227)ippokrates, ppHhh. This theory was first proposed by Hippocrates who argued that the reason for an offspring resembling its parent was due to the fact that every part of the body contributed to the semen’s particles. The theory was first proposed by Hippocrates and suggested that the fusion of the two parents’ seminal substances gave rise to an offspring with a combination of the two parents’ traits.

Later on, Aristotle developed a better concept of heredity in which he attributed the role of the mother parent to the process of conception. According to the theory, the semen substances acquired an active ability of shaping the new embryo. The theory which banked on the concept of blending further claimed that every part of the woman’s body was contained in the menstrual blood. During copulation, the motion of the sperm would shape the menstrual blood into a new organism thereby producing qualitative changes in the matter of the female organism. Aristotle in his arguments expounded on Hippocrates concept of blending in which the male and female traits combined in a blending fashion to form a mixture of the traits in the offspring.

The concept of blending as supported by both Hippocrates and Aristotle in the sense that it assumes basic concepts of heredity that later came to be understood by modern scientists. The concept of incomplete dominance and that of co-dominance explain the special cases in which one allele does not dominate over the other in the expression of a certain trait. Incomplete dominance is a form of intermediate inheritance whereby the trait in the offspring is a mixture of the traits expressed in the parents (Wade, pp 94). While the concept of blending may almost mean something similar, it is flawed in that it assumed every trait in the body is inherited in a similar fashion. This cannot be further from the truth as the concept of complete dominance has proved. In fact, incomplete dominance is prevalent in traits such as skin color and eye color. The concept of co-dominance is different from incomplete dominance in the sense that it leads to the formation of a new phenotype but still expressing the two alleles. An example of this concept is in the formation of blood group AB when alleles A and B are both expressed.

Epistasis is a form of inheritance which explains the different traits achieved in offsprings when the trait is dependent on the action of two or more different genes. For example, the shape of the comb of a chicken is dependent on the action of two different genes that are not allelic in nature. This means that even though the genotypic ratios of the offspring traits may follow the pattern of independent assortment, the phenotypic ratios produce somewhat different results. The concept goes along to bash the concept of blending which supposed that one trait must only be controlled by one gene and that every part contributed one particle to the semen. The concept of blending is therefore erroneous because not all traits are controlled by the action of a single gene.

The concept of blending is further inconsistent with the concept of pleiotropy that is proven to be true by modern research. Pleiotropy entails the combined influence of two distinctly different traits by the action of one single gene. The reason for this concept is that one gene may code for a product that is required by more than one cell of the body. A ‘disadvantage’ of this concept is that a mutation of the pleiotropy gene may consequently lead to an effect on all or some of the different traits at once. Albinism and sickle cell anemia are some of the examples that involve a pleiotropic gene in their expression. This concept is in contradiction with the blending concept because the latter has no provision for such traits that are controlled by one single gene. The concept of blending cannot explain scenarios where such traits are expressed and may lead to the question of why an offspring tends to exhibit a certain set of traits from either of their parents. The explanation for this is, however, due to the traits being controlled by a single gene.

It is also common to come across traits that are controlled by more than one different and non-allelic gene. Such traits are referred to as polygenic traits by virtue of their having many genes controlling them. One example of such a trait is height which therefore means that an offspring may not exactly acquire the same height as either of their parents’. Other examples of traits controlled by polygenes include weight and skin color. The concept of blending assumed that the resulting trait in an offspring would have a combination of its parents’ traits and theus this combination would be an average. This is however not true as polygenic traits have a wide range of possibilities because of their polygenic nature.

It is understandable that philosophers like Hippocrates and Aristotle proposed the concept of blending perhaps due to a lack of empirical experimentation at the time. However, studies done after their hypotheses have confirmed that hereditary is achieved in a non-blending fashion and that it is dependent on many concepts. Each trait is therefore inherited independent of all the others.


Works cited

Hippokrates, , and Mark J. Schiefsky. On Ancient Medicine. Leiden: Brill, 2005. Print.

Wade, Nicholas. A Troublesome Inheritance: Genes, Race and Human History. , 2015. Print.

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