The Origin of Population Genetics

The Origin of Population Genetics

Throughout history, people have made observations about how characteristic traits/morphological features that are highly visible (phenotypical), are passed on from generation to generation, in living organisms. From observations made by agrarian livestock farmers to epigenesis and preformationist embryology as the concepts that arose in the 1700’s, to those who simply noticed that parents and offspring often looked alike; No one really knew that DNA existed, let alone the structures and functions genes.

A breakthrough came during the later part of the 1800’s, when Gregor Mendel hypothesized that discrete units of inheritance existed in living organisms- a conclusion made based on his observations during his experiments with the pea plant. By his postulation, and by his evidence, he opened the doors to a latter of experimentation and subsequent discovery that would perpetuate on into the modern era and our present day, whereby we have come to understand a great deal of information about genetic material, more so then ever before in recorded history. (See, epigenome
; proteome; microbiome)

By the middle and later part of the 1900s, evidence emerged setting apart specific units of inheritance, nucleic acid, as the molecular unit that carried heritable information. This was determined in 1944, by Avery, MacLeod and McCarty when they published the results of their work, revealing the transformation principle that is Deoxyribonucleic acid (DNA), as a material existing in most all living organisms. A belief held by some involved in biological or genetic studies was that the “structure of DNA held the key to understanding its function.” (pp. 120) This is a central dogma in Bioligy: DNA > RNA> Proteins

From there, James Watson and Francis Crick set out to determine this structure with certainty. They were to make one of the most notable discoveries in the field of biology, which was that DNA is a double helical structure. As it turns out, “the assumption that a molecule’s function would be clarified more easily once it’s general structure was determined, proved to be correct.” (“Essentials of Genetics, 6th ed., Klug, Cummings, Spencer. Ch. 9, pp. 189, Pearson Prentice Hall, 2007)

The gene variations observed along chromosomes thereafter, led to the understanding that complex macromolecules synthesized the location or displacement of genes that account for not only genotypical but phenotypical traits.

Historically, evidence from Mendelian genetics was first used to argue against Darwin but nevertheless, the study of inheritance in genetics would establish a mechanism for evolution by explaining mutations and variations that Darwin’s theory emphasized. The synthesis of Darwinism and Mendelism, which marked the birth of modern population genetics, was achieved by a long and tortuous route (cf. Provine 1971)
The idea of Mendelism and Darwinism in connection, stirred up great debate and controversy amongst segregated communities of supporters. Initial arguments were central to the fact that Darwin’s theorized mechanism of evolutionary change by natural selection was not widely excepted, from the time that Origin of the Species was published in 1859 and well into the twentieth century. The dominant approach to the study of heredity in the time prior to the synthesis of population genetics was biometry. Biometry was a study that focused on the statistical analysis of the phenotypic variation found in natural populations and not units of inheritance. Biometricians believed in Darwinian gradualism and tended to focus on continuously varying traits. Mendel’s work in contrast, painted a clear picture of inheritance from a standpoint that explained phenotypical variation and characteristics as determined by discrete units of inheritance (genes) that accounted for variation of traits as heritable units. Mendelians supported the notion of discontinuous variation and single step mutations but not cumulative variations. Eventually the empirical evidence that pointed to an indisputable link between Darwin’s theory and Mendelian genetics was undeniable, being recognized by a lineage of contributory supporters that promoted the fusion of both.
A new group of geneticists, such as R.A. Fisher, J.B.S. Haldane and Sewall Wright devised not just a qualitative but a quantitative mathematical prose that examined the effects of selection and mating in evolutionary processes by combining biometrics with Mendelian genetics. Modern synthesis that connected the reasons behind variation within a population as a result of selection acting on discrete mutations as manifest by multiple-gene inheritance, leading gradually to speciation over time… Population Genetics was born. Since the advent of the field, population geneticists have made monumental contributions to the identification of alleles(gene) frequencies in populations as it relates to the evolutionary processes of natural selection, genetic drift, mutation and gene flow. The phenomena of adaptation and speciation continue to be explained by studies in the field.
Resources:
Genetics and the Modern Synthesis (lecture, Sherrie Lyons)
Population Genetics; The Origin of Population Genetics ( Stanford Encyclopedia of Philosophy Copyright © 2006 by Samir Okasha. http://plato.stanford.edu/entries/population-genetics/)

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