With the great discoveries of the 20th century was that of the role of DNA in heritability and the maintenance of life. Each of our cells contains almost two meters (6.5 ft) of DNA coiled within it. The study of DNA is still ongoing, but some of the discoveries so far have been a bit weird.
Table of Contents
- 1. Heterosis or Hybrid Vigor
- 2. Our DNA was a choice made by our first ancestors.
- 3. We opted to adaptive mutation or Neofunctionalization
- 4. Now we actually can have Three-Parent Babies
- 5. Mosaicism
- 6. The swapping of the chromosome led to who we are today!
- 7. Jumping genes
- 8. 8 percent of your DNA is derived from viruses that invaded your ancestors
- 9. Biological dark matter?
- 10. Epigenetics
1. Heterosis or Hybrid Vigor
We all know that inbreeding usually doesn’t end well and that it is probably not best to marry a close relative. Charles II, the king of Spain in the late 1600s, was inbred. A glance at his biography and his portrait will show that this was not a good idea.
But somehow strangely enough when you breed two inbred individuals from different families together, the offspring will often show a level of physical fitness well above either parent and sometimes more than the general population. This effect is known as heterosis or hybrid vigor. For an inbred individual to survive, they must have some valuable traits to offset the detrimental ones. An individual who has been inbred from different families will have different sets of genes. The cross will benefit from the good dominant traits and hide the negative recessive traits. This also explains the current trend of crossbreeding purebred dogs.
2. Our DNA was a choice made by our first ancestors.
The life forms on earth share similar genetic structures. The four building blocks of DNA are found wherever life is found. Two plausible methods as to why are the structure similar was given. Either there was a single instance of life-forming, and all the descendants inherited the usage of those four bases, or these are the only four bases that can be used to form stable DNA. For testing it, chemicals having a similar structure as the original bases were created. After giving these chemicals to cells, it was discovered that they were incorporated into DNA. The synthetic DNA, which was formed in this way, had structure and function very similar to natural DNA. This result suggests that the DNA we all have is the result of choice made billions of years ago by our first ancestors.
3. We opted to adaptive mutation or Neofunctionalization
The human genome consists of 20,000 genes that codes for proteins. Most of the genes are very similar to each other and are mutated versions of one another. When we compared the sequences of genes, scientists can make accurate guesses as to what a gene does. But how did we end up with copies of genes to mutate? Mutations are often deadly, but if you have two genes to play with, one can mutate freely so long as the other remains active, allowing one gene to evolve to fulfill a new role. This process is called neofunctionalization.
4. Now we actually can have Three-Parent Babies
Mitochondria are known as the powerhouses of our cells. It is thought that mitochondria are simple cells that invaded our cells at some point in the distant past. This has been suggested because the mitochondria in the body maintain their DNA and replicate on their own. When an embryo forms, it inherits half its genome from its mother and a half from its father. But all of the mitochondria are formed in the mother’s egg. If a mutation has occurred in those mitochondria, then all of the offspring’s mitochondria will be mutated. This is dangerous! For preventing it, potential treatment has been developed that would essentially create a baby with three parents.
A sperm would fertilize the mother’s egg as normal, but then the nucleus that is formed would be removed from the embryonic cell and placed in an egg that has had its nucleus removed. This cell now will have the DNA of its mother and father, and the mitochondria of a third person as well.
If a mutation happens when an embryo is young, say eight or 16 cells, then all of the cells formed from the mutated cell will inherit the mutation, which will lead to patches of the adult organism having the mutation while others don’t. This can lead to visible changes, such as patches of hair, localized diseases, or even skin. In humans, it can be possible to see stripes that occur when two colored cell types develop together. Sometimes there is a fusion of two zygotes, which has two sets of DNA in them. This fusion will lead to organisms ending up with patches of each type of cell. In this case of mosaicism, the organism is referred to as a chimera.
6. The swapping of the chromosome led to who we are today!
Humans have 23 pairs of chromosomes, and chimpanzees have 24 pairs. If humans are related to chimps, how can we account for this difference? It can be predicted that two of the chimpanzee chromosomes are fused at some point after chimps and humans had diverged. When we take a look at human chromosome 2, it looks very similar to two shorter chimp chromosomes. Chromosome 2 even has two sets of features, where other chromosomes only have one. How did this happen?
Well, when chromosomes are being copied, they often undergo a process known as recombination, which is swapping of similar areas between pairs of chromosomes. This serves an evolutionary purpose in that it mixes up DNA to allow for greater variation. However, it sometimes goes wrong, and the swapping occurs between the wrong pairs of chromosomes. At some point in the past, this happened to our ancestors, two chromosomes fused to form one and hence we ended up having 23 pairs
7. Jumping genes
Barbara McClintock discovered that there was a change in color in the same corn kernels, which was caused by part of the genome being removed at certain stages of development. These genes are known as transposons or “jumping genes,” which have been found throughout many genomes. They are sequences of DNA which allows the strand to be cut, a portion of DNA to be removed, and the strand is repaired without removing a piece of DNA.
Almost half of the human genome is linked to these transposable elements. From where did they come? They most likely came from our viral friends that never left our bodies. Researchers are still trying to figure out why these areas of instability have been preserved, but it seems possible that they may allow reorganization and innovation in the genome
8. 8 percent of your DNA is derived from viruses that invaded your ancestors
Are you feeling a bit viral today? Approximately 8 percent of one’s DNA is derived from viruses that invaded their ancestors’ genomes and never left. Some viruses, e.g., retroviruses replicate by inserting their DNA into their hosts. Copies are then made, and the virus spreads. But occasionally, when the virus is integrated, a mutation occurs, which deactivates it. This “dead” virus then remains inside the genome and is copied every time the cell is copied. If the virus integrates with a cell that will one day form an egg or sperm cell, then it will be passed on to every cell in the offspring. In this way, incorporated viruses build up inside of the genomes over time. If a virus entered the genome recently, then only very closely related species should have it. If it entered long ago, then many related species must share it. One such virus has been found in nearly all mammals and is thought to have come from infection 100 million years ago.
9. Biological dark matter?
About 40% to 50% of the genetic information found in our GI tract does not match anything that has ever been classified before, not plant, animal, fungus, virus, or bacteria. We have no clue what it is. Biologists call it “dark biological matter.
Epigenetics is the study of the changes that can be made to DNA without changing its actual sequence of the DNA itself. Chemical modifications to the DNA can make a gene more or less active. This imprinting can have large effects on offspring health. Two disorders known as Angelman syndrome and Prader-Willi syndrome are caused by the inheritance of the same genetic information but have widely differing symptoms. If the DNA is from your mother, you will develop Prader-Willi syndrome. If the DNA is from your father, you will develop Angelman syndrome.