What is Molecular Basis of Inheritance?

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Molecular basis of inheritance is basically the study of genes, hereditary and genetic variations. It helps us in understanding how an offspring shares similar features with its parents. DNA, RNA, and genetic code are responsible for transmitting genes from parents to offspring and are the fundamentals of the molecular basis of inheritance.


Traits are inherited over generations. Variations too happen due to recombinations. Genetic materials of most organisms are called the DNA (Deoxyribonucleic Acid). It is primarily responsible for the transfer of the traits in organisms. In viruses, RNA is the genetic material. 

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Importance of DNA

On viewing a cell under a microscope, we can find a nucleus. A nucleus contains all genetic materials. Thread-like structures called nucleolus and chromatin are present inside the nucleus. Chromosomes are condensed chromatin. Every single gene points to a particular trait, a chromosome has thousands of genes withinside it.

 Humans have 23 pairs of homologous chromosomes (46 in number). Inside every cell of a living organism, there is a fixed number of chromosomes. Chromosome numbers may differ among species, each chromosome houses thousands of genes.

A DNA is a double-stranded structure withinside a gene, which is primarily responsible for traits like skin color and eye color. In short, DNA plays the most important role in molecular inheritance. The fact that DNA is the genetic material was proved by Alfred Hershey and Martha Chase in the year 1952, after performing a bacteriophage experiment.  


Structures of DNA and RNA

Nucleic Acids


DNA and RNA are the two kinds of nucleic acids present in a group of biomolecules. They play a crucial role in molecular inheritance.


A DNA is a double-stranded helical structure. It is ribbon-like and is found wrapped around each other. It is a polymer. The monomer units of a DNA are deoxyribonucleotides. The length of a DNA is determined by the number of nucleotides. 


RNA (ribonucleic acid) has a structure similar to that of DNA. But it only consists of a single strand. It is a polymer formed by multiple monomer units called ribonucleotides. RNA plays a key role in the molecular basis of inheritance in a few viruses.

3 components in the nucleotide of a DNA or RNA

  1. Pentose Sugar- A monosaccharide with 5 carbon atoms. While RNA has ribose sugar, DNA has deoxyribose sugar.
  2. Phosphate Group- The phosphate group forms the backbone of the polynucleotide chain. It is basically an inorganic salt of phosphorus and pentose sugar.
  3. Nitrogenous base- Purines and pyrimidines are the two forms of nitrogenous bases. They are heterocyclic aromatic organic compounds. Examples are Adenine and Guanine. Pyrimidines also have a structure similar to that of Purines. Cytosine, Uracil and Thymine are examples of pyrimidines. While Uracil is only present in RNA and not in DNA, Thymine is only present in DNA, but not in RNA.

Formation of Polynucleotide


A polynucleotide bond is formed through a 3’-5’ phosphodiester bond. This leads to the formation of nucleic acid chains in DNA or RNA.

Polynucleotide chain in DNA

The polynucleotide chain is composed of phosphate, pentose sugar and nitrogenous bases. The phosphodiester bonds result in the formation of the polynucleotide chain. 

The double helix structure of DNA


The features of DNA are:

  • It has 2 polynucleotide chains
  • Sugar and phosphate are the key components of the helix structure. The nitrogenous bases withinside are paired through Hydrogen bonds.
  • Adenine pairs with thymine with a double bond. Guanine always pairs up with cytosine with a triple bond.
  • Coiling is right-handed.
  • Since the pairing happens between one purine and one pyrimidine, there is always a uniform distance between the two strands of helix. 
  • There is antiparallel polarity between two polynucleotide chains.
  • The pitch of the helix is basically the width of one turn of a helix.

What is a genetic code?

Genetic code was discovered by Marshall Nirenberg in 1968. He won the Nobel prize along with Robert W. Holley and Har Gobind Khorana.

Salient features are:

  • t is applicable universally. 
  • One genetic code specifies one amino acid.
  • A codon is composed of three adjacent nitrogen bases.
  • Initiation codons signal the synthesis of polypeptides.
  • Stop codons signal the termination of the polypeptide chain.

Human genome project

The human genome project was launched on October 1st 1990, and it was finally completed in 2003. It was an international scientific research project for deciding the base pairs that make up human DNA. The project had a significant role to play in the fields of life science, medicine, and biotechnology. 


  • For storing information in the databases.
  • Human genome project aimed at improving tools for data analysis.
  • The project was used for determining sequences of base pairs that make up the human DNA.
  • The project was used for identifying around 25,000 genes in human DNA.

Hence, the concept of molecular basis of inheritance is explained in detail here. 

Read more : Everything you need to know about Mahalwari system


Check your knowledge

      Answer) Molecular basis of inheritance is basically the study of genes, hereditary and genetic variations.

      Answer) Deoxyribonucleic Acid.

      Answer) October 1, 1990.

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