Buzz
Among the most groundbreaking discoveries of the 20th century was unveiling DNA's crucial role in inheritance and sustaining life. Each of our cells holds nearly two meters (6.5 ft) of DNA wrapped tightly inside. The study of DNA is still unfolding, but some of the revelations so far have been quite bizarre.
10. Hybrid Vigor
We are all aware of the dangers of inbreeding, and that marrying a close relative is not advisable. Charles II, who reigned as the king of Spain in the late 1600s, was so heavily inbred that, unlike the usual eight great-grandparents, he had only four. A quick look at his portrait and biography will reveal that this was certainly not a good idea.
However, something fascinating occurs when two inbred individuals from different families are bred together. The offspring often exhibit a higher level of physical fitness compared to either parent, and sometimes even surpass the general population. This phenomenon is known as heterosis, or hybrid vigor. The theory suggests that for an inbred individual to survive, they must possess certain beneficial traits to counterbalance the harmful ones. An inbred individual from another family will have a different genetic makeup. The offspring benefits from the good dominant traits while masking the negative recessive traits. This also explains the ongoing trend of crossbreeding purebred dogs.
9. Epigenetics
Just when you think you have genetics all figured out, a new set of complications emerges. You inherit one gene copy from your mother and one from your father, and you might expect them to interact in a perfectly balanced way. Unfortunately, the differences between the genders run deeper than you might expect.
Epigenetics refers to the study of changes made to DNA without altering its actual sequence. Chemical modifications can make a gene more or less active. This imprinting can have significant effects on the health of offspring. Two disorders—Angelman syndrome and Prader-Willi syndrome—are caused by inheriting the same genetic information, yet they result in drastically different symptoms. The same DNA sequence can lead to varying effects, depending on which parent it is inherited from. If the DNA is from your mother, you’ll develop Prader-Willi syndrome. If the DNA comes from your father, Angelman syndrome will develop.
8. Mosaicism
It is commonly stated that the DNA in all of our cells is identical. This is generally true, except when mutations occur. If a mutation takes place in an early stage of embryonic development, say when the embryo has only eight or 16 cells, then all cells derived from the mutated one will inherit the mutation. This results in certain areas of the adult organism carrying the mutation while others do not. These changes can manifest in visible forms, such as patches of different colored skin or hair, or localized diseases. In humans, it is even possible to observe stripes (called Blaschko’s lines) that appear when two different colored cell types develop together.
Occasionally, two embryos within the same womb can fuse during early development. As a result, their cells intermingle and grow into a single organism. This organism will then carry two distinct sets of DNA. Due to the movement of cells during embryonic growth, the final organism will exhibit patches of each type of cell. This phenomenon, known as mosaicism, results in an organism called a chimera.
7. Repeats
Proteins are encoded in DNA in segments consisting of three base pairs each (codons). During DNA replication, a proofreading process ensures that the copy matches the original. Mutations occur when a mistake slips past the proofreading system, which only happens about once in several million base pairs. However, certain regions are more prone to accumulating mutations than others. Occasionally, there are repeated sequences of the same codon, known as trinucleotide repeats, which complicate the proofreading process.
In Huntington’s disease, the gene responsible contains several CAG repeats in its sequence. If, during replication, an additional CAG set is added, the proofreading mechanism may overlook it, as there are CAG repeats on both sides. As a result, when the protein is produced, it ends up with an extra amino acid. Fortunately, there is some flexibility in the protein structure that accommodates these additions. The disease only manifests when the mutation reaches a certain length, and because these errors accumulate across generations, Huntington’s disease tends to worsen with each passing generation.
6. Viral Integration
Do you feel a bit viral today? If so, I wouldn't be shocked. Around 8 percent of your DNA comes from viruses that invaded your ancestors' genomes and stayed there. Some viruses—specifically retroviruses—replicate by inserting their genetic material into the host's DNA. These copies spread as they replicate. However, sometimes, when the virus integrates, a mutation happens that disables it. This 'dead' virus remains within the genome and is copied every time the cell divides. If the virus integrates with a cell that will later become an egg or sperm, it will be passed on to all cells in the offspring. Over time, these incorporated viruses accumulate within genomes.
Because these integrated viruses can be inherited by all offspring, it’s possible to track evolution by the presence of a deactivated virus. If the virus entered the genome recently, it will likely only appear in closely related species. However, if it was integrated long ago, many related species will share it. One such viral remnant has been found in nearly all mammals, believed to have originated from an infection that occurred 100 million years ago.
5. Jumping Genes
With the pleasant weather arriving in the Northern Hemisphere, it's time to clean the barbecue. But before you munch on your corn on the cob, take a moment to examine it. You might be looking at something worthy of a Nobel Prize. Occasionally, corn kernels will show a variety of colors, even though they share identical genetics. Barbara McClintock discovered that this color variation was caused by part of the genome being removed during specific stages of development. These mobile genetic elements, known as transposons or 'jumping genes,' have been found across many genomes. Essentially, these sequences of DNA allow the strand to be cut, a portion removed, and the strand repaired, without the missing piece.
Parts of our genome can be quite mobile, shifting in and out, which sounds like a dangerous situation. Indeed, many diseases are tied to these moving genetic elements. However, nearly half of the human genome is made up of these transposable elements. But where did they originate? Most likely, they came from viruses that integrated into our DNA long ago and never fully left. While researchers continue to investigate why these unstable regions remain in our genome, it seems plausible that they offer flexibility for genetic reorganization and even innovation.
4. Neofunctionalization: A process where genes acquire new roles after a mutation.
The human genome contains approximately 20,000 genes that code for proteins. Many of these genes are strikingly similar, often appearing as mutated versions of one another. By analyzing their sequences, scientists can make educated predictions about the function of a gene. But how did we end up with these gene duplicates?
It’s likely that transposable elements were involved. If a piece of DNA jumps out after being copied and then cuts into a new DNA strand, two identical genes emerge. While mutations can be harmful, having two copies means one can mutate without jeopardizing the other. This gives one gene the opportunity to evolve a new function, a process called neofunctionalization.
3. Three-Parent Babies
The human genome consists of all the genetic material located in the nuclei of our cells. However, there is another form of DNA in our bodies: the mitochondria. Often referred to as the powerhouse of the cell, mitochondria are believed to be ancient cells that once invaded our ancestors' cells. This theory is supported by the fact that mitochondria have their own DNA and replicate independently of the host cell.
When an embryo develops, it inherits half of its genetic material from the mother and half from the father. However, all of the mitochondria in the embryo come from the mother’s egg. If a mutation occurs in the mitochondrial DNA, all of the offspring’s mitochondria will carry the mutation, which can be fatal. To prevent this, a potential treatment has been developed that creates a ‘three-parent’ baby.
In this process, a sperm fertilizes the mother’s egg as usual. However, the nucleus of the fertilized egg is removed and transferred into an egg whose nucleus has already been discarded. This new cell will have the combined genetic material from the mother and father, but will also carry the mitochondria from a third donor.
2. Chromosome Rearranging
Chromosomes are large DNA structures that help organize the genetic information in eukaryotic cells. Humans have 23 pairs of chromosomes, while chimpanzees have 24 pairs. Given the evolutionary relationship between humans and chimps, how can we explain this discrepancy? It’s possible that two of the chimp chromosomes fused after humans and chimps evolved separately. If you look closely at human chromosome 2, it appears to be a fusion of two smaller chimp chromosomes. Notably, chromosome 2 has two centromeres, unlike other chromosomes which typically only have one. How could this occur?
During chromosome replication, a process called recombination occurs. This is where similar segments of DNA are exchanged between paired chromosomes, promoting genetic diversity. However, recombination doesn’t always go as planned. Sometimes, the wrong segments get swapped, which can cause diseases or result in the fusion of entire chromosomes. This likely happened in the past with our ancestors, leading to the formation of our larger chromosome 2 and contributing to our evolutionary history.
1. Custom DNA
All living organisms on Earth share the same fundamental genetic blueprint. The same four nucleotide bases—the basic components of DNA—are found in every form of life. There are two main theories that could explain this uniformity. Either these four bases are the only ones capable of forming stable DNA, or life began just once, and all descendants inherited the use of these four bases.
To test these hypotheses, researchers created chemical analogs with structures nearly identical to the original DNA bases. After introducing these analogs into cells, it was found that they were successfully incorporated into DNA. The resulting DNA exhibited a structure and function similar to natural DNA. This suggests that the DNA we all use today might be the result of a critical decision made billions of years ago by the very first living organism.
