How Does Molecular Homology Support Evolution?

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Molecular Homology is the similarity among organisms at the bio-molecular level. It studies the similarity of patterns in the nucleotide sequences of DNA or amino acid sequences of polypeptides as evidence for a common evolutionary origin.

Molecular homology shows phylogenetic relationships among various organisms. In molecular homology, the similarities and differences of DNA and the genetic code reflect the shared ancestry of life.

DNA comparisons are one of the prime workings of molecular homological studies that can show how related species are and how they share common ancestry.

How Does Molecular Homology Support Evolution? In modern biology, molecular homology showcases the evolutionary relationships between various organisms in the modern taxa of classification at the molecular level. It helps in understanding how the present-day organisms share common ancestors by performing a comparative study of the genetic materials and polynucleotide sequences of amino acids.

Modern evolutionary biology is strongly dedicated to working not just on the philosophical sayings, but on the molecular level study to find strong evidence of evolutionary history and the connecting links between organisms.

Molecular homological studies are strongly dedicated to the similarities between biological molecules that are present in the living organisms like the DNA, genes, amino acid polypeptide chains, etc.

Such a study can reflect shared evolutionary ancestry amongst the organisms and indicate how ancestral organisms have evolved to the present-day ones.

Molecular homology states that at the most basic level, all living organisms share the same genetic material (DNA); the same, or highly similar, genetic codes; the same basic process of gene expression (replication, transcription, and translation); and possess the same molecular building blocks, such as amino acids.

Let’s know more about molecular homology and its supporting concepts in evolution…

How Does Molecular Homology Support Evolution: 5 Evidences You Must Know

Same like the anatomical structures, the molecular structures also indicate the evidence of common ancestors for all forms of life by molecular homology.

The molecular homology is reflected in the universality of DNA, genetic code, DNA replication, gene expression, etc.

In general, the relatedness of groups of organisms is reflected in the similarity of their DNA sequences that show clear evidence of evolution.

Here’re the 5 evidences of how molecular homology supports evolution. Let’s know more about these:

1. All living organisms have DNA as the genetic material

All living organisms have genes made up of DNA. DNA is a polymer of nucleotides. Each nucleotide is composed of a nitrogenous base, a five-carbon pentose sugar, and a phosphate group.

DNA is the chemical unit of life and the genes that are the sections of DNA express genetic characteristics in all living organisms.

This concept is the same for all life forms on earth. Meaning that the same structure of DNA is present in each and every living organism irrespective of its classification.

The presence of the same kind of DNA structure in all organisms suggests that all living things are descended from a common ancestor and that this ancestor also had DNA as its genetic material.

DNA, the chemical unit of life makes genes that are the unit of inheritance. This shows that all the present-day organisms share the same DNA features because they were inherited from the common ancestor via. the genes.

Although there are some differences that have occurred in the DNA sequence due to mutation over the course of evolution that make each species different.

But nevertheless, in general, the relatedness of groups of organisms is reflected in the similarity of their DNA sequences and finely shows that all present-day organisms have evolved from past extinct or non-extinct ones.

The DNA structure of all organisms on earth let it be an earthworm or a shark or a human, or anything else, it is the same.

This means that the DNA structure contains the same pentose sugar, the same nitrogenous base (with Adenine/Guanine/Cytosine/Thymine), and the same phosphate group bonded together with the same covalent and hydrogen bonds in all living organisms. This is one evidence of molecular homology.

Example: It is seen that 90% of human genes match with cats. It is also seen that chimpanzees are our closest living evolutionary relatives that share 96% genes similar to humans.

2. Different species have the same, or highly similar, genetic codes

All organisms on earth have genetic codes that are the same or highly similar in nature. And so the function of genetic code to produce a specific protein is also the same or highly similar in nature in all organisms.

The relationship between the sequence of amino acids in a protein polypeptide chain and the nucleotide sequence of DNA & mRNA is called Genetic code. The genetic code consists of 64 codons.

The genetic code is in an encrypted form in DNA that can’t be directly translated into proteins, and so, DNA is first transcribed to mRNA so that it can be finely translated into proteins.

This conversion of DNA to mRNA to proteins has been happening in the same way since the origin of life from simple prokaryotic organisms to the present day more complex organisms like humans. And in the process, some similar types of proteins are also being produced in all organisms.

It is why the evidence of a common ancestor for all of life according to molecular homology is reflected in the universality of DNA as the genetic material and also in the near universality of the genetic code that is decoded from that DNA.

The genetic code for protein-coding genes is nearly universal in all eukaryotes and prokaryotes.

Theoretically, the genetic code is universal. This means that the same codon will make the same amino acid in all organisms.

Example: In both humans and bacteria, a codon made of three thymine DNA-letters will code for an amino acid called Phenylalanine. There are about twenty amino acids, and about 64 codons.

3. All organisms have the same basic process of gene expression

Molecular homology also states that all organisms have the same basic process of gene expression that includes DNA replication, transcription, and then the translation to proteins.

DNA replication is done in order to create multiple copies of the same DNA during cell division. Transcription is done in order to copy a gene’s DNA sequence to make an mRNA molecule. And translation is done, in order to produce a specific amino acid chain from the mRNA sequence.

This overall basic process of gene expression is the same in all living organisms from simple prokaryotic ones to complex eukaryotic ones.

The DNA structure is the same, thus the RNA too, and so the proteins are produced too.

Molecular homology doesn’t say that all the gene expression processes work in a 100% similar way in all types of organisms at the molecular level, but the overall working processes (DNA to mRNA to Proteins) are kind of a same.

This means that the proteins that will be produced after gene expressions can show different characteristics in different organisms, and it totally depends on what way the gene was expressed. But that gene expression will always include the process of replication, transcription, and translation strictly which is same everywhere.

Molecular homology concludes that the gene expression process is strongly dedicated through the involvement of molecules like nucleotides, hydrogen, carbon, nitrogen, ammonia, etc. in the same way in all living organisms.

4. All have amino acids as the same molecular building blocks

In any organism in the earth, if you see, you will find that all have amino acids as the same molecular building blocks of proteins.

Proteins are made up of the polypeptide chain of amino acids during the gene expression process. These proteins can express various genetic characteristics in each and every living organism.

The consistency of the genetic code after translating between nucleic acids and amino acids produces proteins of different amino acids.

Each amino acid has information on how organisms should be. That’s how the genetic information in the DNA is expressed in the body with the help of various amino acids and their proteins.

Therefore, the structure of the amino acids are the same in all organisms, but its presence can vary.

This simply means that life on earth is complex and varied, but every living organism on the planet builds its proteins from the same set of 20 amino acids. And, these amino acids are produced the same way in all organisms by gene expression.

Here, Molecular homology states that every living organism uses that same system i.e. basically, every three pieces of DNA become 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.

Example: Humans, cows, chickens, and chimpanzees all have the same type of gene that has the same genetic codes that encode the same hormone insulin. According to molecular homology, it shows that humans, cows, chickens, and chimpanzees had a common ancestor. But, the insulin produced is a bit different between human, cows, and chicken, the reason for which is provided in the next evidence number 5.

5. Presence of homologous genes in different species

A homologous gene (or homolog) is a gene inherited in two species by a common ancestor that can be similar in its DNA sequence. This indicates how those species are evolutionarily related to one another.

The basic idea behind this concept is that two species have the same gene because they inherited it from a common ancestor.

For example, humans, cows, chickens, and chimpanzees all have a gene that encodes the hormone insulin, because this gene was already present in their last common ancestor.

In general, the more DNA differences in homologous genes or amino acid differences in the proteins they encode between two species, the more distantly the species are related.

For example, human and chimpanzee insulin proteins are much more similar (about 98% identical) than human and chicken insulin proteins (about 64% identical), reflecting that humans and chimpanzees are more closely related than humans and chickens.

Mutations actually occur when homologous genes are inherited generation after generation. When a lot of mutations occur than speciation (formation of new species) also occurs in the future generation. This leads to the formation of new different species that also shows genetic similarities with their ancestors.

For instance, everyone’s DNA is different because all person on earth has a 99.9% matching DNA and only a 0.1% DNA is different from person to person. This 0.1% change is due to the varying effects of mutations that make everyone’s DNA unique.

This also indicates that after millions of years maybe there will be the formation of new human species that will be different from the present-day Homo sapiens.

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