For Darwinian selection to produce evolutionary changes, some of the variation in traits between individuals must be inherited. In addition, the inheritance mechanism must maintain variation in the absence of selection. The mixture of heredity, the mechanism postulated in Darwin`s time, would quickly homogenize hereditary variations between individuals. Under heredity, any observable variation between individuals would be environmental, and the mechanism postulated by Darwin would not be able to bring about lasting change. At that time, it was generally accepted that this “mixed heritage”, in which the characterization of descendants in terms of such complex traits as strength, power, size, intelligence, etc. tends to be between those of the two parents, could not be accommodated by the Mendelian scheme, although Udny Yule* showed beyond any doubt in 1902 that the same mechanism met the requirements of the typical Mendelian and Mendeler type. could satisfy. the type of inheritance. The importance of this article was not recognized, and it was only when the later work of Nilsson-Ehle, † East, Emerson, and Fisher‖ showed that the mixture of heredity was essentially Mendelian and was controlled by several factors that individually lacked dominance, that the dispute ceased.
The main difference between heredity and particulate inheritance is that in mixed inheritance, offspring is a mixture of both parents, while in particulate inheritance, offspring is a combination of both parents. Considering how difficult it is to distinguish zygotes with different [genotypic] formulas, even if dominance is relatively perfect, one would expect a population of [descendant] individuals with almost continuous quantitative variation if dominance is imperfect or absent. This gives an indication of a Mendelian interpretation of heritage previously known as mixing. Darwin`s theory of evolution changed biology in the mid-nineteenth century. Darwin, however, had an inaccurate understanding of heredity and his belief in the mixture of heredity was problematic. Because mixed inheritance ultimately leads to homogenized populations full of intermediate genotypes, it cannot explain how genetic variation can persist over the course of evolution (Charlesworth and Charlesworth, 2009). It was only with the rediscovery of Mendelian genetics at the beginning of the twentieth century that a possible solution could be found. It is important to note that Mendel treated genes as discrete units, allowing for a mathematical formulation of population genetics. Despite the rediscovery of Mendelian genetics and the pioneering work of biologists and statisticians (Castle, 1903; Pearson, 1904) there was still some confusion, and at a meeting of the Royal Society of Medicine in 1908, it was claimed that dominant mutations would increase in frequency until phenotypes reach Mendelian ratios of 3:1 (Provine, 2001). Something about this claim seemed to be R.C.
Punnett, who passed the question on to his cricketer friend G.H. Hardy. Hardy was one of the UK`s leading mathematicians and quickly found a solution. In a 1908 letter to the journal Science, Hardy first wrote, “I should have expected the very simple point I want to make to be familiar to biologists,” before using binomial expansion to show that genotype frequencies will reach stable equilibrium after random mating generation (Hardy, 1908). Unbeknownst to Hardy, a German doctor named Wilhelm Weinberg had published a similar paper on the same topic six months earlier. Weinberg derived a general principle of equilibrium for a single place with two separating alleles (Weinberg, 1908). Bateson became aware of Gregor Mendel`s work in the summer of 1900 and soon realized that Mendel`s principles of heredity offered both a theoretical explanation of unmixed heredity and an experimental approach to identifying hereditary patterns. Bateson and Saunders interpreted and published their data in the first five-part series, Reports to the Evolution Committee of the Royal Society, 1-5 (London: Harrison, 1902-1909).
In the first report, Bateson and Saunders used this new understanding to explain various cases, including the work of a respected and contemporary physician, Archibald Garrod, who studied a rare abnormality, alcaptonuria, in which a person produces urine that darkens when exposed to air. The condition is particularly likely to occur in descendants of first-degree marriages, as would be predicted according to Mendelian principles. Armed with this realization, Garrod developed his concept in the book Inborn Errors of Metabolism (1909) and is considered the founder of biochemical genetics. In a letter to Alfred Wallace dated February 6, 1866, Darwin mentions that he conducted hybridization experiments with pea plants similar to those of Gregor Mendel, and how he obtained segregated (unmixed) varieties, effectively refuting his theory of pangenesis with mixing: there was still controversy. While the mathematics of heredity was clear for discrete phenotypic characteristics, attempts to characterize the inheritance of the continuous characteristics that characterized a species and defined its differentiation from other species had not yielded such simple mathematical rules. Without such a theory, it was not clear how natural selection could cause changes in such traits. As part of the blending of inheritance, the value an individual has for a trait would be a mixture of the values that the individual`s parents have for that trait. Mixed heredity is an early theory that states that the offspring receives a mixture of hereditary substances from their parents. Therefore, the offspring has intermediate characteristics between those of the parents.
In other words, the mixed theory states that two parents produce offspring with traits that lie between those of the parents. Therefore, the offspring is only an average between the two different characteristics of their parents. As an example to explain this theory, we can consider the crossing of two varieties that produce white and red flowers. When this cross produces offspring of pink color, it shows a mixed heritage. The fusion of inheritance states that descendants are always an intermediate mixture of their parents` characteristics. In contrast, particulate inheritance indicates that the offspring receives discrete units from their parents. Fusion theory is no longer an accepted theory, while particulate heredity is an accepted theory in biology. Genetic variation is inherited and maintained according to particulate inheritance, while genetic variation is not possible according to mixed inheritance. So here is the summary of the difference between fusion and particulate inheritance. All living organisms have a clearly defined cellular architecture controlled by the genes they inherited from their parents. The branch of science that deals with heredity and variation is known as genetics. The history of genes and genetics dates back to Gregor Mendel`s work on pea plants in the nineteenth century.
Before Mendel`s work, pangenesis and the mixture of heredity theories were the accepted theories in the biological world to explain heredity in living organisms, but Mendel`s work explained heredity on the basis of scientific experiments. He is honored with the title of “Father of Genetics.” He observed that various characteristics such as size, flower color, etc. are controlled by the particulate matter in the cell, which he called factors.