Universal Genetic Code (Evolution) — Evidence & Examples

Evidence of Evolution: Universal Genetic Code

All organisms use DNA to store genetic information (with the exception of some viruses). They all use the same four bases ($\text{G, A, C,}$ and $\text{T}$—or $\text{U}$ if you're talking about RNA) and make the same amino acids. This is why DNA provides us with the universal genetic code. Because of the genetic code, a lot of very different species have the same genes. Similarities and differences between the same gene in two different species can tell us how closely related they are.

Studying Mutations

DNA mutations for specific genes occur at a relatively steady rate which allows us to create a molecular clock. Molecular clocks use the rate of mutation in a segment of DNA common between two species to estimate how long ago the two species shared a common ancestor. If there are few differences in the gene, then the two species shared a common ancestor relatively recently.

What Is an Example?

For example, look at a segment of DNA that codes for hemoglobin in multiple animals. Gorillas and humans only have a one nucleotide difference in this segment, showing one mutation. Humans and chickens have 45 nucleotide differences, showing 45 mutations. This shows the relative distance in relatedness between humans, gorillas, and chickens.

How Do Scientists Use This Information?

The use of DNA to determine relationships among species helps us create better evolutionary trees. We used to determine relatedness based on physical appearance, but we now know that appearance can be misleading.

DNA: The Universal Genetic Code

(Video) DNA Spells Evolution

by NOVA PBS Official

The molecules DNA and RNA are the genetic building blocks of all organisms. In other words, they provide the universal genetic code. This is powerful evidence that all organisms share common ancestors. We actually have 82% of our DNA in common with dogs.

In this video, NOVA PBS Official explains how DNA acts as evidence of evolution.

Why Is DNA Considered a Universal Genetic Code?

DNA is considered a universal genetic code because every known living organism has genes made of DNA. Bacteria, fungi, cats, plants, and you: every organism uses DNA to store genetic information.

All organisms also use DNA to transcribe RNA, and then they translate that RNA into proteins. Every living organism uses that same system. Basically, every three pieces of DNA becomes one amino acid. The amino acid it becomes depends upon that three-letter sequence, which is called a codon.

Pretty much every organism uses the same translation system, with a few bacteria having some more unique amino acids.

How Is DNA Evidence of Evolution?

Since every living organism uses the system of DNA $\rightarrow$ RNA $\rightarrow$ Protein, DNA is considered to be a universal genetic code. And because all cells come from parent cells, cells are able to inherit DNA from their parents. This process is known as heredity. For example, if a dog has a thick fur coat and it has puppies that also have a thick fur coat, then you know those puppies inherited DNA that coded for proteins that would end up creating that fluffy fur.

What Are Conserved Genes?

You can tell how related two species are by looking at conserved genes. Conserved genes are often very similar between even very different species. For example, the genes for ribosomes are almost exactly the same in all eukaryote species. Differences as small as a single nucleotide can be used to determine how long ago two species diverged.

For larger evolutionary differences, think about the use of DNA as a trait in itself. If you use DNA, then your parent must have used DNA, and so did their parent, and their parent before them. You all used the same system of DNA $\rightarrow$ RNA $\rightarrow$ Protein for millions or even tens of millions of years.

What About RNA?

The system that turns RNA into proteins can have some slight differences. You can find divergence in evolution using that system. For example, the same DNA sequence in a human and in a bacterium could result in a different protein. This makes sense because prokaryotes, like bacteria, and eukaryotes, like humans, diverged a very long time ago.