Explore the riveting realm of genetics in this series. Beginning with the iconic discovery of the DNA double helix, we traverse breakthroughs and genetic mapping, unraveling the blueprint of life. Stay tuned for Part 2's deep dive into DNA's intricacies. |
The realm of genetics has been an exciting and rapidly evolving field, unveiling the intricate language that defines our very existence. [8] This article delves into the fascinating world of genetics, tracing the major breakthroughs that have shaped our understanding of DNA, its structure, and the journey of mapping the genetic code. In a two-part series, we will explore the history of genetic discoveries and the conceptualization and mapping of DNA, shedding light on the blueprint of life itself.
Part 1: A Journey Through Genetic Breakthroughs
The Double Helix and Its Constituent Parts
The journey into the heart of genetics begins with the iconic discovery of the DNA double helix. In 1953, James Watson and Francis Crick, alongside the contributions of Rosalind Franklin and Maurice Wilkins, unveiled the structure of DNA. [14] This groundbreaking revelation showcased DNA as a double-stranded molecule, resembling a twisted ladder. Each strand of the helix consists of nucleotides, the basic building blocks of DNA. [12]
Figure 01: The double helix structure of DNA molecule.
Nucleotides themselves comprise three components: a phosphate group, a deoxyribose sugar molecule, and one of four nitrogenous bases—adenine (A), cytosine (C), guanine (G), or thymine (T). The arrangement of these bases along the DNA strands holds the key to our genetic information. [16]
1.1 Mappingthe Genetic Code
Genetic mapping is a way to identify exactly which chromosome has which gene and exactly pinpointing where that gene lies on that particular chromosome. Mapping also acts as a method in determining which gene is most likely to recombine based on the distance betweentwo genes.
[10] The distance between two genes is measured in units known as centimorgan or map units, these terms are interchangeable. A centimorgan is a distance between genes for which one productof meiosis in one hundred is recombinant.[11][12] The farther two genes are from each other, the more likely they are going to recombine. If it were closer, the opposite would occur.[13]
Figure 02: Gene Mapping
Advancements in genetics led to the ambitious task of mapping the human genome, often referred to as the "book of life." The Human Genome Project, initiated in 1990, aimed to sequenceand map all the genes of the human species. [1] It was completed in 2003, providing a comprehensive genetic blueprint for humanity. Part 2: Conceptualizing and Mapping the Genetic Code 2.1 DNA Strands in Our Cells
Deoxyribonucleic acid (abbreviated DNA) is the molecule that carries genetic information for the development and functioning of an organism. [3] DNA is made of two linked strands that wind around each other to resemble a twisted ladder — a shape known as a double helix.
Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T). The two strands are connected by chemical bonds between the bases: adenine bonds with thymine, and cytosine bonds with guanine.[5] The sequence of the bases alongDNA’s backbone encodes biological information, such as the instructions for making a protein or RNA molecule.
Figure 03: DNA Standards
Inside each of our cells lies a remarkable, coiled thread of DNA known as a chromosome. Humans typicallyhave 46 chromosomes, 23 pairs, in their cells. The size and length of DNA strands can vary significantly. [7] If we were to unravel and stretch out the DNA in a single human cell, it would extend to around 6 feet long! To put that into perspective, the average human body contains trillions of cells, each with its own unique DNA. 2.2 Pieces of Genetic Information
Within these lengthy strandsof DNA, we find an astonishing amount of geneticinformation. The human genome is estimated to contain roughly 3 billion base pairs, encompassing thousands of genes that code for proteins. [9] Genes are the functional units of DNA, each with specific instructions for building and maintaining our bodies. [6]
PART 3: What Is The “Language” Of The Genetic Code, And How Is It Identified And Mapped? 3.0 The Languageof the Genetic Code
Consider nucleicacids and amino acids to be two distinctlanguages. DNA and RNAcommunicate in nucleic acid (A, U/T, G, and C) terms, whereas proteins communicate in amino acid terms. The tRNA (transfer RNA) molecule is the "interpreter" in the cell since it speaks both languages! [4] Codons are groups of three nucleotides that code for a certain amino acid.
These codons are recognised by the tRNA molecule and base pair with the complementary sequence known as anticodon.Because they can read nucleicacid sentences (as mRNA codons) and supplythe relevant amino acids, tRNA molecules operate as translators. [11]
Figure 04: Two representations of tRNA structure. At left, the classic clover-leaf, splayed out for simplicity. At right, a more accurate representation of the tRNA in pseudo-3D. (E.V. Wong CC-BY-NC-SA 10.5: tRNA are Rather Odd Ducks)
DNA is often likenedto a language, and its code is written in the sequenceof nitrogenous bases.Each triplet of these bases, called a codon, corresponds to a specific amino acid [13]—the building blocksof proteins. This genetic code is universalamong all living organisms on Earth. 3.1 Identifying and Mapping Genes
Genes, the functional segmentsof DNA, are identified through a combination of computational analysis, laboratory experiments, and comparisons to known gene sequences. [2] Each gene is given a unique name and location on a chromosome, much like a street address in a city grid.
In addition to genes, there are genetic groupings called haplogroups. These are defined by specific genetic variations that are often used to trace ancestry and migration patterns. [15] Haplogroups are also identified and mapped based on genetic markers and shared genetic traits. Conclusion
The geneticcode is a marvel of nature, an intricate language that holds the blueprint for life. Part 1 of this series has explored the major breakthroughs in genetics, including the discovery of the DNA double helix and the ambitious Human Genome Project. In Part 2, we delve into the conceptualization and mapping of DNA, from the length and size of DNA strands to the language of the genetic code. With each discovery, we inch closer to unraveling the mysteries of our genetic heritage,opening up new frontiers in medicine, evolution, and human identity.
About the Author:
Maheen Javed, M.D. graduated as a medical doctor in 2020 with experience in medical research, medical writing and other diverse areas in the medical field. She currently practices in a hospital and works as a professional medical writer and researcher, writing technical articles on a wide variety of topics in the medical field, such as mental health, diabetes, women's health, cancer research, psychiatry, neurology, surgery and mental health.
About the editor:
Brian Hoy has over 20 years of experience in the medical device industry and business formation, supporting the full lifecycle with global scope. Brian consults for industry and provides general advisory and off-hours support.
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