Genetics: Past, Present, and Future

Introduction

Genetics is the study of heredity and the variation of inherited elements known as genes. Although scientists have long known that an offspring’s traits come from its parents, the findings of Darwin and Mendel have really allowed scientists to begin to understand how and why genetic variation occurs. With advances in scientific research and informatics, genetics has become increasingly significant in revealing the causes of diseases and the differences among individuals and species.

 Past

For centuries, western religion contributed to the widespread acceptance of the theory of “creationism,” which refers to the literal interpretation of the Bible in which God created the Earth and all modern, immutable species around the year 4000 B.C.E. Advances in geology and observations of incremental changes of species in the fossil record over time led to skepticism that eventually brought forth the development of the theories that make up the foundation of selection theory.

The first major theory of genetics was hypothesized by Hippocrates in fifth century B.C.E. Hippocrates’ theory is known as the “bricks and mortar” theory of genetics and states that taxonoomical material consists of physical substances originating from each part of the body and is concentrated in the male semen, which develops into a human within the womb. Further, he believed that physical characteristics are “acquired.” For example, a champion weight lifter who develops large biceps through training has “big bicep” parts, which would be passed to the lifter’s offspring through his sperm and result in a big-bicepped child (1).

Decades after Hippocrates’ proposition, Aristotle challenged his ideas by noting that handicapped individuals with missing limbs could go on to produce children with normal limbs. Additionally, he criticized the bricks and mortar theory by explaining that people can pass on traits that appear later with age. For example, a man with a full head of hair may conceive a child and then experience baldness years later. Thus, the “hair parts” were passed on while the “bald parts” occurred later with age, contradicting Hippocrates (1).

Before the era of modern genetic Carl von Linné, better known as Linnaeus, developed today’s two-part scientific naming system (1). Later in the late 18th century, French naturalist Jean-Baptiste Lamarck proposed the first comprehensive theory of evolution. Although Linnaeus held the traditional opinion that species were created with certain traits that never changed, Lamarck contradicted the creationist belief that species were immutable; he claimed that species change in response to their environments by inheriting characteristics that their parents acquire over their lifetimes. For example, for a giraffe to reach leaves to eat off a tall tree, it would have to stretch its neck. Because giraffes need to eat leaves, the giraffes that acquired longer necks from stretching would be able to pass on their modified neck lengths to their offspring and eventually contribute to a new characteristic to the entire giraffe species (1). Following Lamarck, geologist Charles Lyell contradicted the biblical statement that the earth was about 5000 years old by proposing that contemporary geographical formations such as mountains and deserts were formed by natural physical processes that occurred over millions of years. These discoveries bolstered the argument that changes over time are the result of natural rather than divine intervention.

While a student, Charles Darwin was selected to serve as the “naturalist” on board the ship HMS Beagle on a voyage to map the waters along South America’s coast (1). By recording extensive observations, Darwin developed his theory of natural selection, the major mechanism of evolution. Natural selection states that genetic differences can make individuals more or less suited for their environment. Those who are better suited survive go on to produce offspring, making the favorable traits characteristic of the population over time; those species with less favorable traits face extinction. Upon returning from his expedition, Darwin spent over twenty years collecting data and writing to publish his theories in his book On the Origin of Species in 1859. The reaction to Origin at publication was “immediate, international, and intense but also mixed” across both scientific and religious communities, as evolution contradicted the widely accepted principles of creationism (1). Continuing with his studies, Darwin attempted to explain the mechanism for natural selection in 1868 by proposing his theory of “pangenesis”—an updated version of Hippocrates’ brick and mortar approach. Pangenesis dictates that both mother and father secrete “gemmules” which aggregate in reproductive organs and combine to form the embryo. However, the setback to pangenesis was that after generations of blending within a population, members would be genetically identical, lacking variation and inhibiting natural selection. For instance, if a young child has a watercolor set with multiple distinct colors and blends the colors together repeatedly with use, eventually each section of the palate would have a uniform brownish hue (1).

The mechanism of natural selection was illustrated by the research of Austrian monk Gregor Mendel in 1864. By studying pea plants, he proposed that inheritance came about by transmission of discrete units, known as “alleles”, rather than through blending. He said that in reproduction both the mother and father contribute a unit of their own traits, and the offspring inherits one of them perfectly intact and is free from influence of the other. Although Mendel published in 1864, the scientific community largely ignored his research, and the significance of his work was not realized until 1900 when several scientists discovered that their own findings lined up perfectly with those of Mendel (2).

The rediscovery of Mendel’s work led to the progress in genetics studies of the twentieth century. In the early twentieth century, Walter Sutton and Theodor Boveri extended Mendelian principles with their “Chromosomal Theory of Inheritance,” which states that an organism’s hereditary material resides in its chromosomes (3). By the mid-twentieth century, it was proved that DNA is the genetic material that made up chromosomes, and Watson and Crick discovered DNA’s “double helix” structure, laying the groundwork for modern molecular genetics advances (3). In 1953 the Modern Synthesis of Genetics was formulated, linking Mendelian genetics to Darwin’s theory of evolution by confirming that Mendel’s theory of discrete unit inheritance is the basis of natural selection (3). Later in the twentieth and early 21st century, genetics advances were geared toward the molecular level, and the dawn of the information age brought about modern genomics science as it is known today. The field of genetic engineering, or modifying the DNA of organisms, emerged in 1972 when the first altered molecule of DNA was constructed as “recombinant DNA.” In the following year, a functioning E.coli bacteriophage cell was produced using such recombinant DNA (3). In 1977, the Sanger group developed techniques to sequence, or decode, DNA and successfully used their methods to publish the entire genetic code of a particular strand of E. coli. In conjunction with technological advances of the era, the biomedical technique of polymerase chain reaction (PCR) was developed, significantly expediting the process of DNA sequencing and leading to the development of automated DNA sequencers in 1986.

The progression of DNA sequencing technology led to the launch of the Human Genome Project in 1990. This effort, funded by the US government, was a collaboration of the National Institute of Health (NIH), the Department of Energy, and international partners aiming to sequence all three billion letters of the human genome, or genetic code. According to the NIH, “The Human Genome Project’s goal was to provide researchers with powerful tools to understand the genetic factors in human disease, paving the way for new strategies for their diagnosis, treatment and prevention” (4). Leading up to their publication in 2001, the first bacterial, yeast, and flowering plant genomes were sequenced (3). The Human Genome Project accomplished the mapping and sequencing of five prototype organisms meant to serve as a basis for interpretation of the human code, much like the Rosetta Stone allowed for interpretation of multiple languages (5).

Once completed, all generated data from the Human Genome Project were made accessible on the Internet to accelerate global medical discovery. The availability of this “human instruction book” was said by Doctor Francis Collins, Director of the NIH and head of HGP, to “mark the starting point of the genomic era in biology and medicine” (5).

Present

Due to the extent of genetic knowledge acquired over time, it is now recognized that the adaptation of genetic code to the environment is the force behind evolution. However, these alterations occur gradually over the course of many generations. Consequently each individual carries around several potentially deleterious genes, related to their ethnic background and ancestral environment (6). According to Queen’s Medical Center, “Every disease has, in addition to environmental influences, genetic components that collectively determine the likelihood of a specific disease, age of onset, and severity,” (6). With advances in genetics and technology, scientists now have the capacity to identify some of these alterations and are learning more about how genes interact with other genes and the environment to cause disease or other health effects. For example, the Human Genome Project has already fueled the discovery of more than 1,800 disease genes. Additionally, researchers can find a gene suspected to cause a disease in a matter of days—a process that took years prior to HGP—and there are currently over 2000 genetic tests available for human conditions (4). These tools empower physicians to assess patients’ risks for acquisition of diseases and diagnose genetic conditions.

Because genetics enables professionals to identify differences in genes and their additive effects on patients’ health, medical treatments can now be tailored to more effectively complement an individual’s unique genetic code. Combining genetic knowledge with computational technology, the modern field of bioinformatics enables professionals to handle large amounts of data, which makes such analysis of individual patients’ genomes possible. Consider the field of pharmacogenomics: a field that examines how genetic variation affects an individual’s response to a drug. According to the NIH, pharmacogenomic tests can already identify whether or not a breast cancer patient will respond to the drug Herceptin, whether an AIDS patient should take the drug Abacavir, or what the correct dose of the blood-thinner Warfarin should be,” (4). Focused development of these technologies in bioinformatics is dramatically reducing the price of genome sequencing, from about $100 million in 2001 to just over $1,000 today (7).

As stated by the NIH, “Having the complete sequence of the human genome is similar to having all the pages of a manual needed to make the human body. The challenge now is to determine how to read the contents of these pages and understand how all of these many, complex parts work together in human health and disease” (4). One illustration of this attempt of comprehension is the 2005 launching of the HapMap project, an international collaboration aimed at documenting common genetic variation, or “haplotypes”, in the human genome. These haplotypes interest genetics researchers because they tend to be similar within various global populations. So comparing haplotypes, which are chunks of genetic information, instead of individual letters in DNA sequences accelerates the search for genes involved in common human diseases. In 2010, the third phase of this project was published with information from 11 of these populations, making it the largest survey of genetic variation performed. The HapMap project has already yielded results in finding genetic factors in conditions ranging from age-related blindness to obesity (4).

Modern knowledge of genetics allows for new types of health care involving genetic engineering, or the alteration of genetic material. Because genetic engineers can insert and remove portions of DNA in organisms using enzymes and advanced technologies, new types of more efficient plants and animals are being created, and chemicals such as insulin, human growth hormone, and interferon are currently being produced for human genes in bacteria for health care benefits. Substances produced from genetically engineered organisms in this way have lowered costs and side effects associated with replacing missing human body chemicals (8). Methods in gene therapy, the replacement or removal of defective genes to correct errors that cause genetic diseases, are also under development in hopes of providing a more targeted, efficient, and effective approach to genetic disease treatment (9).

Future

As stated by geneticists Wolf, Lindell, and Backstrom, “Only recently have we entered an era where deciphering the molecular basis of speciation is within reach,” (10). The advances in bioinformatics have made comparison of genomes across species efficient, bringing the possibility of a comprehensive model of the evolutionary history of life closer to reality.

In addition to speciation insights, future decades bring promise of enhanced understanding the genetic bases underlying diseases. Despite many important genetic discoveries, the genetics of complex diseases such as heart disease remain “far from clear” (4). With a progressive understanding of the molecular and genomic factors at play in diseases, scientists anticipate more effective medical treatments with fewer side effects in the future. Several new initiatives have been launched in effort to achieve this deeper understanding:

1. The Cancer Genome Atlas aims to identify all the genetic abnormalities seen in 50 major types of cancer (11).

2. National Human Genome Research Institute’s (NHGRI) public small molecule library provides academic researchers with a database to chart biological pathways, which can subsequently be used to model the genome in experiments and serve as starting points for drug development.  (11).

3. The Department of Energy’s Genomes to Life focuses on the genomic studies of single-cell organisms in hopes that once researchers understand how life functions on a microbial level, they can “use the capabilities of these organisms to help meet many of our national challenges in energy and the environment,” (11).

4. The Structural Genomics Consortium is an international effort studying the structure of the proteins encoded by the genomes of organisms put forth by the United Kingdom’s Wellcome Trust and pharmaceutical companies. These three-dimensional structures are critical in drug design, diagnosis and treatment of disease, and biological understanding. The information will be published in a public database (11).

Furthermore, the NIH is concentrating efforts in making genome sequencing more affordable and thus more widely available to the public, enabling easier diagnosis, management, and treatment of diseases (4). Leaders in the field forecast individualized analysis of individual genomes will result in a new form of preventative and personalized medicine in healthcare in the decades to come. A healthcare professional’s interpretation of a patient’s DNA sequence will allow for planning preventative lifestyle choices and crafting disease treatment to target the problem areas in the patient’s specific genome. Bioinformatics will enable genetically literate healthcare professionals to determine whether a drug will have adverse effects on a patient, optimize the therapies that will likely be most successful for a patient with a specific disease, and to identify the high-risk and low-risk diseases for the patient (6). Further, scientists claim, “by the year 2020, gene-based designer drugs are likely to be available for conditions like diabetes, Alzheimer’s disease, hypertension, and many other disorders. Cancer treatment will precisely target the molecular fingerprints of particular tumors, genetic information will be used routinely to give patients more appropriate drug therapy, and the diagnosis and treatment of mental illness will be transformed” (5).

The Human Genome Project has also raised discussions on the ethical, legal, and social implications of the future of genetics. Policymakers are currently considering how to regulate the use of genomic information inside and outside of medical settings to ensure safety and privacy of individuals, as well as addressing health disparities across populations (12). Along with understanding medical conditions, genetics researchers are becoming increasingly able to connect DNA variation with conditions such as intelligence and personality traits—making the ethical, legal, and social implications of genetics research more significant (4). The impact of genomics on concepts such as race, ethnicity, kinship, individual and group identity, health, disease, and “normality” for traits and behaviors will need to be discussed (5). Controversial practices including human cloning, eugenics, and medical discrimination are some of the possibilities that come with the anticipated routes of genetic advancement (8).

Contact Mackenzie Foley at

mackenzie.a.foley.16@dartmouth.edu

 

References

1. G. Carey, History of Genetics (2010). Available at http://psych.colorado.edu/~carey/hgss2/pdfiles/Ch%2001%20History%20of%20Genetics.pdf (25 March 2013)

2. A.H. Sturtevant, A History of Genetics (CSHL Press, New York, 2001).

3. A. Mandal, History of Genetics. Available at http://www.news-medical.net/health/History-of-Genetics.aspx (25 March 2013)

4. National Institute of Health, Human Genome Project (2010). Available at http://report.nih.gov/NIHfactsheets/ViewFactSheet.aspx?csid=45&key=H#H (25 March 2013)

5. F. Collins, Testimony before the Subcommittee on Health Committee on Energy and Commerce US House of Representatives, 22 May 2003.

6. S. Donlon, MS, Genetics: The Future of Medicine. Available at http://www.queensmedicalcenter.net/services/90-genetics-the-future-of-medicine (25 March 2013)

7. NHGRI Genome Sequencing Program, DNA Sequencing Costs (2013). Available at http://www.genome.gov/sequencingcosts/ (25 March 2013)

8. Oswego City School District Regents Prep, Genetic Engineering (2011). Available at http://regentsprep.org/regents/biology/2011%20Web%20Pages/Genetics-%20Genetic%20Engineering%20page.htm (25 March 2013)

9. F. Collins, The Language of Life:DNA and the Revolution in Personalized Medicine (HarperCollins, New York, NY, 2010), pp. 253-5.

10. J. B. W. Wolf, J. Lindell, N. Backström, Phil. Trans. R. Soc. B 365, 1717-27 (2010).

11. National Human Genome Research Institute, What’s Next? Turning Genomics Vision Into Reality (2006). Available at http://www.genome.gov/11006944 (25 March 2013)

12. M. E. French, J. B. Moore. Harnessing Genetics to Prevent Disease & Promote Health: A State Policy Guide. Washington, DC: Partnership for Prevention; 2003.