Molecular Basis of Inheritance

What is the Molecular Basis of Inheritance?

The subject which involves the study of genes, genetic variations and heredity is known as the molecular basis of inheritance. It illustrates how an offspring looks identical to the parents. DNA, RNA and genetic code form the basis of the molecular basis of inheritance. They convey the hereditary genes from the parents to the offspring.

DNA and RNA are the two types of nucleic acid found in living systems. DNA acts as the genetic material in most of the living organisms, RNA acts as a genetic material in viruses. RNA mostly functions as a messenger and in some cases as a catalytic module.

DNA

According to scientists, The complete form of DNA is Deoxyribonucleic Acid. Deoxyribonucleic Acid (DNA) is a two-stranded patch with a double helix shape. It consists of four essential ingredients, i.e., adenine (A), cytosine (C), guanine (G), and thymine (T) with sugar and phosphate. DNA contains the vital inheritable information of a living organism. 

In 1953, James Watson and Francis Crick discovered and found out the two- stranded structure of DNA (deoxyribonucleic acid). Two scientists named Watson and Crick kept ahead of a 3D design of DNA. The two beaches of polynucleotides coil around each other, forming a double helix or a crooked graduation-like structure. 

The structure of DNA motes could be indirect or direct. DNA generally occurs as natural chromosomes in eukaryotes and indirect chromosomes in prokaryotes (unicellular organisms). 

If we see a cell under a microscope, we can see a nucleus which is the region including all genetic materials. The nucleus comprises nucleolus and chromatin. Chromatin is a thread-like structure which compresses to form chromosomes located with genes. Each chromosome has thousands of genes and each gene points to a specific characteristic.  The number of chromosomes inside each cell of living organisms is fixed. For example, humans have 23 pairs of homologous chromosomes, that is, 46 in number. In various species, chromosome numbers may be distinct.  A gene is composed of a double-stranded structure called DNA; various parts of DNA are accountable for various characteristics like skin colour, hair colour, eye colour etc. This illustrates that DNA is accountable for molecular inheritance. In 1952, Alfred Hershey and Martha Chase proved that DNA is the genetic material by conducting a bacteriophage experiment. 

Hence, it forms the fundamental part of the molecular basis of inheritance.

RNA

According to scientists, the complete form of RNA is Ribonucleic acid. RNA is a single-stranded nucleic acid patch. RNA performs an essential part in cellular metabolism.  

A biopolymer of RNA consists of only one strand. It consists of four essential ingredients, i.e., adenine (A), cytosine (C), guanine (G), and uracil(U) with sugar and phosphate.

The stability and structural variations of more cells may make them susceptible to destruction. In the case of a generator transfer RNA patch without a methyl group (tRNAiMet), revision at position 58 will render the patch inoperable; the cellular mechanisms that maintain tRNA quality will destroy the inoperative chain.

The RNA molecules can also form complexes with molecules known as ribonucleoproteins (RNPs). Scientists have demonstrated that the RNA portion of one cellular RNP acts as a natural catalyst, a function that was previously thought to be exclusive to proteins.

RNA plays a central role in the molecular basis of inheritance. It connects DNA and proteins. 

The central dogma is an important part of the molecular basis of inheritance which explains the flow of genetic information in two ways, that is; 

*DNA to RNA

*RNA – DNA – mRNA – protein (in retroviruses)

Genetic Code 

The genetic code may be defined as the sequence of nucleotides in DNA and RNA which determines the amino acid sequence of proteins. Proteins are not made directly from DNA, therefore a messenger RNA (mRNA) directs information of the protein from DNA. The four nucleotides which compose RNA are, Adenine, Guanine, Cytosine and Uracil. The three adjacent nucleotides constitute the codon. 

There are a total of 64 codons out of which three do not code for amino acid, whereas the rest 61 specify the 20 amino acids. The AUG codon has dual functions, it not only indicates the start of protein but also codes for Methionine. Methionine and Tryptophan are the amino acids which are coded by a single codon. One codon codes only for one amino acid. Hence it is unambiguous in nature. UAA.UAG and UGA are stop codons for the protein synthesis process.

Therefore, with characteristics like non-overlapping, universality, triplet nature and non-ambiguous genetic forms an important part of the molecular basis of inheritance.

Conclusion

In conclusion, DNA forms the base for life and RNA may be the first inheritable material in the organism. The fact that RNA can function in every aspect of life means that it’s considered the first inheritable material to be evolved. RNA can act as an inheritable material and as a catalyst too. 

Human genome project was a mega project and an excellent example of the molecular basis of inheritance. The technique of the molecular basis of inheritance has also been used in DNA fingerprinting. It has proven to be an advantage for various fields like genetic biodiversity, forensic science and evolutionary biology.