Explainer: The Basics of DNA and Genetic Systems
While there is great diversity among living things, we all have one thing in common—we all rely on a genetic system made up of DNA and/or RNA.
But how do genetic systems work, and to what extent do they vary across species?
This graphic by Anne-Lise Paris explores the basics of DNA and genetic systems, including how they’re structured, and how they differ across species.
Composition of Genetic Systems: DNA and RNA
A genetic system is essentially a set of instructions that dictate our genetic makeup—what we look like and how we interact with our environment.
This set of instructions is stored in nucleic acids, the two main types being deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA is made up of four molecules, known as nucleotides: Adenine (A), Thymine (T), Cytosine ( C), and Guanine (G). These nucleotides are grouped in sets of two, which are called base pairs.
Size of Genomes Across Different Organisms
Human DNA is made up of approximately 3.2 billion base pairs that are tightly wound up and stored in our cells. If you were to unwind and measure the DNA stored in a single human cell, it would be about 2 meters (6.5 feet) long!
This lengthy DNA is stored in pairs of chromosomes. A full collection of chromosomes, or an entire set of genetic information, is referred to as a genome.
Genomes vary in size, depending on the organism. Here is a look at 24 different species and the size of their genomes, from animals and plants to bacteria and viruses:
|Organism||Kingdom||Size of genomes (number of base pairs)|
|Hepatitis D virus||Virus||1,700|
The Marbled Lungfish has the largest known animal genome. Its genome is made up of 130 billion base pairs, which is about 126.8 billion more than the average human genome.
Comparatively, small viruses and bacteria have fewer base pairs. The Hepatitis D virus has only 1,700 base pairs, while E. coli bacteria has 4.6 million. Interestingly, research has not found a link between the size of a species’ genome and the organism’s size or complexity.
In fact, there are still a ton of unanswered questions in the field of genome research. Why do some species have small genomes? Why do some have a ton of redundant DNA? These are still questions being investigated by scientists today.
This article was published as a part of Visual Capitalist's Creator Program, which features data-driven visuals from some of our favorite Creators around the world.
Visualizing the Evolution of Vision and the Eye
The eye is one of the most complex organs in biology. We illustrate its evolution from a simple photoreceptor cell to a complex structure.
Roadmapping the Evolution of the Eye
Throughout history, numerous creatures have evolved increasingly complex eyes in response to different selective pressures.
Not all organisms, however, experience the same pressures. It’s why some creatures today still have eyes that are quite simple, or why some have no eyes at all. These organisms exemplify eyes that are “frozen” in time. They provide snapshots of the past, or “checkpoints” of how the eye has transformed throughout its evolutionary journey.
Scientists study the genes, anatomy, and vision of these creatures to figure out a roadmap of how the eye came to be. And so, we put together an evolutionary graphic timeline of the eye’s different stages using several candidate species.
Let’s take a look at how the eye has formed throughout time.
Where Vision Comes From
The retina is a layer of nerve tissue, often at the back of the eye, that is sensitive to light.
When light hits it, specialized cells called photoreceptors transform light energy into electrical signals and send them to the brain. Then the brain processes these electrical signals into images, creating vision.
The earliest form of vision arose in unicellular organisms. Containing simple nerve cells that can only distinguish light from dark, they are the most common eye in existence today.
The ability to detect shapes, direction, and color comes from all of the add-ons evolution introduces to these cells.
Two Major Types of Eyes
Two major eye types are dominant across species. Despite having different shapes or specialized parts, improved vision in both eye types is a product of small, gradual changes that optimize the physics of light.
Simple eyes are actually quite complex, but get their name because they consist of one individual unit.
Some mollusks and all of the higher vertebrates, like birds, reptiles, or humans, have simple eyes.
Simple eyes evolved from a pigment cup, slowly folding inwards with time into the shape we recognize today. Specialized structures like the lens, cornea, and pupil arose to help improve the focus of light on the retina. This helps create sharper, clearer images for the brain to process.
Compound eyes are formed by repeating the same basic units of photoreceptors called ommatidia. Each ommatidium is similar to a simple eye, composed of lenses and photoreceptors.
Grouped together, ommatidia form a geodesic pattern that is commonly seen in insects and crustaceans.
Our understanding of the evolution of the compound eye is a bit murky, but we know that rudimentary ommatidia evolved into larger, grouped structures that maximize light capture.
In environments like caves, the deep subsurface, or the ocean floor where little to no light exists, compound eyes are useful for producing vision that gives even the slightest advantage over other species.
How Will Vision Evolve?
Our increasing dependency on technology and digital devices may be ushering in the advent of a new eye shape.
The muscles around the eye stretch to shift the lens when staring at something close by. The eye’s round shape elongates in response to this muscle strain.
Screen time with cellphones, tablets, and computers has risen dramatically over the years, especially during the COVID-19 pandemic. Recent studies are already reporting rises in childhood myopia, the inability to see far away. Since the pandemic, cases have increased by 17%, affecting almost 37% of schoolchildren.
Other evolutionary opportunities for our eyes are currently less obvious. It remains to be seen whether advanced corrective therapies, like corneal transplants or visual prosthetics, will have any long-term evolutionary impact on the eye.
For now, colored contacts and wearable tech may be our peek into the future of vision.
Visualizing the Composition of Blood
Despite its simple appearance, blood is made up of many microscopic elements. This infographic visualizes the composition of blood.
The Composition of Blood
Have you ever wondered what blood is made up of?
With the average adult possessing five to six liters of blood in the body, this fluid is vital to our lives, circulating oxygen through the body and serving many different functions.
Despite its simple, deep-red appearance, blood is comprised of many tiny chemical components. This infographic visualizes the composition of blood and the microscopic contents in it.
What is Blood Made Up Of?
There are two main components that comprise blood:
- Plasma – 55%
Plasma is the fluid or aqueous part of blood, making up more than half of blood content.
- Formed elements – 45%
Formed elements refer to the cells, platelets, and cell fragments that are suspended in the plasma.
Plasma is primarily made up of water (91%), salts, and enzymes, but it also carries important proteins and components that serve many bodily functions.
Plasma proteins make up 7% of plasma contents and are created in the liver. These include:
These proteins keep fluids from leaking out of blood vessels into other parts of the body. They also transport important molecules like calcium and help neutralize toxins.
These play an important role in clotting blood and fighting infections and are also transporters of hormones, minerals, and fats.
- Fibrinogen and Prothrombin
Both of these proteins help stop bleeding by facilitating the creation of blood clots during wound-healing.
Water and proteins make up 98% of plasma in blood. The other 2% is made up of small traces of chemical byproducts and cellular waste, including electrolytes, glucose, and other nutrients.
There are three categories of formed elements in blood: platelets, white blood cells, and red blood cells. Red blood cells make up 99% of formed elements, with the other 1% comprised of platelets and white blood cells.
- Platelets (Thrombocytes)
Platelets are cells from the immune system with the primary function of forming clots to reduce bleeding from wounds. This makes them critical not only for small wounds like cuts but also for surgeries and traumatic injuries.
- White blood cells (Leukocytes)
White blood cells protect our bodies from infection. There are five types of white blood cells with different roles in fighting infections: some attack foreign cells and viruses, some produce antibodies, some clean up dead cells, and some respond to allergens.
- Red blood cells (Erythrocytes)
Red blood cells deliver fresh oxygen and nutrients all over the body. They contain a special protein called hemoglobin, which carries oxygen and gives blood its bright red color.
The lifespan of a typical red blood cell is around 120 days, after which it dies and is replaced by a new cell. Our bodies are constantly producing red blood cells in the bone marrow, at a rate of millions of cells per second.
Abnormal Red Blood Cells
Normal red blood cells are round, flattened disks that are thinner in the middle. However, certain diseases and medical therapies can change the shape of red blood cells in different ways.
Here are the types of abnormal red blood cells and their associated diseases:
Sickle cell anemia is a well-known disease that affects the shape of red blood cells. Unlike normal, round red blood cells, cells associated with sickle cell disease are crescent- or sickle-shaped, which can slow and block blood flow.
Other common causes of abnormally shaped red blood cells are thalassemia, hereditary blood disorders, iron deficiency anemia, and liver disease. Identifying abnormal blood cells plays an important role in diagnosing the underlying causes and in finding treatments.
The Functions of Blood
We know that blood is vital, but what does it actually do in the body?
For starters, here are some of the functions of blood:
- Blood transports oxygen to different parts of the body, providing an energy source. It also delivers carbon dioxide to the lungs for exhalation.
- The platelets, white blood cells, and plasma proteins in blood play an important role in fighting infections and clotting.
- Blood transports the body’s waste products to the kidneys and liver, which filter it and recirculate clean blood.
- Blood helps regulate the body’s internal temperature by absorbing and distributing heat throughout the body.
While we all know that we can’t live without blood, it serves many different functions in the body that we often don’t notice. For humans and many other organisms alike, blood is an integral component that keeps us alive and going.
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