Written by: Zafeena Ather
Email: zafeena.ather@gmail.com
Introduction
‘Genetics is the scientific study of genes and heredity—of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence.’
Understanding genetics is a voyage through the science of inheritance and a way of unraveling the mysteries of human variation. Many of our physical functions and appearances are determined by the intricate code encoded within our DNA. In this article, we will dig into the interesting field of genetics, learning more about what they are and how they play a part in the many ways that people differ.
History of Genetics
While several philosophers like Aristotle and Hippocrates introduced ideas related to genetics, Gregor Mendel, a Moravian Augustinian friar working in the 19th century in Brno, was the first to study genetics scientifically. He carried out numerous cross-pollination experiments between different species of plants to prove his findings of alleles; dominant and recessive genes. He developed a brilliant hypothesis that established a prototype for genetics that is still used today for gene discovery and understanding inheritance.
Figure 1. ‘Gregor Mendel, Father of Genetics’
Figure 2. Aristotle’s Theory of Inheritance
What are Genes?
Genes, which serve as the biological code for our bodies, are made up of DNA sequences. The nucleotides are the building blocks of DNA; adenine (A), cytosine (C), guanine (G), and thymine (T) act on a combination of nucleotides, known as a codon, to produce amino acids, which combine to form protein. Considered the workhorses of our cells, proteins serve a variety of purposes in our bodies, hence these genes contain instructions for constructing and maintaining our bodies. Every cell in our body has chromosomes, thread-like structures where these genes are arranged.
The human genome is the entire set of genetic material in an individual. It has around 3 billion base pairs, which allows plenty of genetic variability.
Figure 3. Genome assembly composition
How Genes Affect Humans Physically:
Some characteristics show a stronger influence (e.g. height), others an intermediate level (e.g. personality traits), and some more complex heritabilities.
Ethnicity and Ancestry
Ethnicity and lineage in humans are mainly heavily dependent on genetics. Genetic variations can be used to track an individual's genetic heritage, revealing details about their ancestors. Courtesy of advances in genetic testing and analysis, individuals can now study the genealogy of their relatives through sites like 23andMe and AncestryDNA.
These genetic ancestry tests examine specific DNA markers to offer data regarding a person's origins and ancestors' pathways of migration. They can shed light on the intricate web of human history and displacement by revealing linkages to specific ethnic groups.
Figure 4. DNA Testing Kit - 23andMe
Talent
Genetics also has an impact on an individual's characteristics and skills. Even though no single gene can predict a person's aptitude for a particular ability, genetic variances can influence some aspects that assist in the cultivation of talent. For example, genes associated with cognitive function can influence intellectual abilities, but genes associated with muscle growth and coordination can influence athletic ability.
It is vital to emphasize that intelligence is not solely a genetic phenomenon. In addition to practice and training, the environment plays an important role in skill development. Both genetic predisposition and environmental influences are important in the development of talents and skills.
Figure 5. Plum’s Talent Model
Personality Traits
While genetics determine one's physical characteristics and risk for diseases, personality, and behavioral factors are also influenced. According to some studies, personality traits like extroversion, introversion, bluntness, etc. are all influenced by inheritance. However, it is crucial to remember that personality is the consequence of a complex mixture of genetic, environmental, and societal factors.
Genes control the production of neurotransmitters and their absorption in the brain, which determines mood, behavior, and depression. However, a person's personality can change as a result of external factors such as upbringing, experiences, and social interactions.
Figure 6. The brain releasing dopamine and serotonin
Susceptibility to Diseases
Genetics also has a substantial impact on a person's risk of certain diseases. While some diseases are caused exclusively by genetic reasons, others are caused by an intricate collaboration of genetic and environmental factors. For example, some cancers, such as breast and colon cancer, have a strong hereditary component. If a person inherits specific alterations associated with certain cancers, they may have a higher risk of developing them.
Single gene mutations like these contribute to disorders like sickle cell anemia and cystic fibrosis. If a person inherits two copies of the defective gene (one from each parent), they are at risk of acquiring these diseases. Understanding the genetic roots of diseases aids in recognizing illnesses and the development of specialized treatments and preventative measures.
Figure 7. A mutation affecting a chromosome
Physical Changes
Genetics is responsible for the huge range of physical traits that distinguish each individual. Height, skin tone, eye color, and hair texture are just a few examples of genetically determined features. Changes in a single gene, for example, can cause differences in eye color, with specific genetic combinations creating brown, blue, green, and hazel eyes.
Genes can influence metabolism and how our bodies digest food. Some people are more prone to obesity genetically, while others find it easier to maintain a healthy weight. In contrast, several genes interact to influence height. Taller parents often have taller offspring due to the cumulative impact of genes related to bone growth and development.
How Genetic Variation Can Occur:
SNPs, Single Nucleotide Polymorphism, occur when a single nucleotide in the genome differs in paired chromosomes. For example, a SNP may replace the nucleotide cytosine (C) with the nucleotide thymine (T) in a certain stretch of the DNA. It is the most common type of genetic variation. Most SNPs do not affect health or development. However, some of these genetic differences have proven to be very important in the study of human health. SNPs help predict an individual’s response to certain drugs, susceptibility to environmental factors such as toxins, and risk of developing diseases. Research is ongoing to identify SNPs associated with complex diseases such as heart disease, diabetes, and cancer. They can also alter attributes such as eye color.
Figure 10. Nucleotides being replaced
Indels, or insertions and deletions, are mutations that arise when one or more nucleotides in a gene are added or removed. As a result, they have a significant impact on gene function and cause a plethora of genetic illnesses.
In some parts of sequence space, indels are often well tolerated, and their evolutionary impacts on organismal fitness are not distinctly different from those induced by SNPs, at least in terms of the normal functioning of the proteins. However, studies of indels resulting in low fitness have led to positive results.
‘Insertions and deletions are high risk, high reward mutations that represent steep ledges in the fitness landscape.’
Taking into account all features of this way of genetic variation, it has been demonstrated that insertions and deletions have evolutionary and biotechnological significance.
Copy Number Variations (CNVs) are molecular phenomenons in which genome sequences are altered by addition or removal, and the number of copies of genes varies amongst individuals of the same species. These variances can result in disparities in physical characteristics such as height or susceptibility to certain diseases. Chromosome abnormalities manifest themselves in larger-scale changes. Neuropsychiatric disorders such as autism and schizophrenia, as well as other frequent complicated diseases, are caused by chromosomal abnormalities.
Recombination involves the physical breakage, rejoining, or exchange of genetic material either between multiple chromosomes or between different regions of the same chromosome. This process creates genetic diversity that reflects differences in the DNA sequences of different organisms. It occurs through meiosis, the process of cell division that results in the creation of eggs and sperm, so genetic material can recombine. Transduction, transformation, and conjugation are three recombination strategies.
Figure 13. Exchange of Genetic Material
Genetic Engineering and its Development over the Years
Genetic discrimination is also a rising issue in the world, where health plans discriminate against those who have disabilities or who have genetic conditions.
This is one of many reasons why many have turned to newer scientific methods of genetic engineering to fix such issues. For genetic testing to be done safely and appropriately, issues related to it should be discussed with patients so they are aware of the risks and benefits. Issues concerning the privacy and security of individuals' genetic information have grown as genetic testing has become more widely available.
CRISPR-Cas9 is currently the simplest, most versatile, and precise method of genetic manipulation and is causing a buzz in the science world. There is questioning over this procedure and how ethically upright it is to create ‘designer babies.’
The genetic engineering of animals has increased significantly in recent years and alongside this, many ethical concerns have also risen.
Conclusion
Genetics is a fascinating field that has altered our perceptions of life, inheritance, and evolution. Genetics continues to reveal the secrets of life itself. Our rising understanding of genetics holds the promise of improving healthcare, combating hereditary illnesses, and unraveling the secrets of our genetic history. It is a path of discovery that will continue to shape science and medicine's future.
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