Chapter 6

Molecular Basis of Inheritance

Discussion on the Molecular Basis of Inheritance Class 12 NCERT Solutions:

  • The search for genetic material
  • The RNA World or Replication
  • Understanding the term: Transcription 
  • Genetic code
  • Human genome project
  • DNA fingerprinting

In this chapter for Class 12, we will learn about genes and genetics in detail. Our genes determine much of our biological constitution and determine our chances of developing certain diseases and disorders. It is important to learn about them so as to better understand the human body and by extension, ourselves. 

This chapter navigates many subtopics and questions relating to genes and how important they play in heredity and inheritance. The phenomenon of heredity is central to biology, and inheritance is how those genes are passed from generation to generation. We understand how genes influence our traits and characteristics by learning about them.

We’ll also take a closer look at the RNA world or Replication. Transcription and the genetic code are other topics that are also very important to understand and will be explored in this chapter.

Finally, this chapter will also talk about the Human Genome Project. This massive project was undertaken to identify, map, and sequence all of the genes that comprise the human body. We also examine DNA fingerprinting and its importance in forensics and how it aids criminal investigations.

The Molecular Basis of Inheritance NCERT: The search for Genetic Material:

In the 19th century, biologists discovered that the material responsible for heredity was passed from the parent to the child. This theory was based on the principle that organisms inherit their traits from their parents. 

In 1869, German scientist Friedrich Miescher discovered a substance in the cells of animals and humans that contained genetic information. It was called ribonucleic acid (RNA) as it was found in the cellular fluid (the fluid containing water and proteins) called nuclein. Miescher was not aware of what it was or what it did, but he knew for sure that it was found only in the cells of living things.

The story of the discovery of genes is a classic example of scientific discovery. In 1869, a German scientist called Julius Wagner-Jauregg treated an Austrian Archduke with a mysterious illness and discovered that he could cure syphilis by injecting his patients with the blood of animals. 

The following year, another German scientist, Friedrich Miescher, discovered the material that Wagner-Jauregg had used in his syphilis treatment – a material that is now known as DNA. It took 70 years before scientists discovered how DNA was copied and passed onto offspring.

The search for genetic material that makes us who we are has fascinated scientists for ages. In the 19th century, Charles Darwin also acknowledged the fundamental importance of genetics and the inheritance of acquired characters. The 19th-century researchers also found that cell materials such as chlorophyll and proteins were made of tiny building blocks called amines, purines, and pyrimidines. 

The search for the material responsible for the transmission of genetic information is one of the greatest scientific adventures of the 20th century.

According to the RNA world hypothesis, the first self-replicating molecules were RNA, not DNA. DNA is a more recent innovation in the evolution of life. RNA is the first bio-molecule to be considered a molecule in its own right rather than a part of a larger molecule. It is the first molecule to contain the blueprint for making more of itself.

The RNA world hypothesis that a primitive form of RNA was the primary genetic material in early organisms. Some of the earliest cells were single-celled organisms that used RNA to store genetic information, direct other molecules' construction, and transcribe it into DNA.

Transcription refers to the process of copying a section of DNA into RNA, the molecule that carries out the instructions encoded in our genes. In many ways, transcription is the first step in the cellular process of making proteins, the molecules that carry out most of the functions in our bodies. 

The first gene to be sequenced in humans was the gene for transcription factor TFIIIA, one of the proteins responsible for turning genes on and off. Our genes are made up of DNA, which carries our genetic code.

Transcription is the first step in gene expression, the cellular mechanism by which gene sequences are copied into RNA sequences. The RNA molecule contains the same genetic information as the DNA molecule transcribed from it. Still, it is a single-stranded molecule instead of a double-stranded molecule like DNA. 

The transcription process can be divided into three major stages: 

  • Initiation
  • Elongation
  • Termination

Transcription occurs when a molecule of DNA is copied into an RNA molecule. 

What genes are turned on or off in our body, and how are they inherited? How is the activity of genes inherited differently in various tissues and cell types? 

This module will explore the molecular basis of gene regulation and the mechanisms by which genes are turned on and off in living cells. We will also see how this knowledge is used in genetic engineering and other applications of modern biology.

One of the most important questions in biology is how traits are passed from one generation to the next. The answer to this question has been long sought after by geneticists. It has eventually become clear that the process of inheritance is governed by the transcription and translation of genetic material.

This hypothesis is supported by a wealth of genetic data, which has revealed the existence of numerous mechanisms that control the transcription and translation of genetic material. In particular, the observation that the same gene can be turned on or off with relatively little influence from the environment has led many to conclude that the activity of genes determines the mechanism of inheritance.

Most of our genes are transcribed into RNA, which is then used as a template for protein synthesis. However, some genes are transcribed into a different type of RNA known as long non-coding RNA (lncRNA). These lncRNA molecules often function like protein-coding genes, sometimes regulating the expression of protein-coding genes.

The human genome project provides information about the composition of the human genome. It is now possible to study the structure and function of the genome and determine how and why the gene sequences in the genome encode the proteins that comprise the cell's body.

This module of Molecular Basis Of Inheritance Class 12 NCERT will study these processes, detailed topics and their solution.  By which genes are transcribed and translated into proteins and explore how the activity of genes is regulated and how mutations in gene sequences can lead to diseases.

For many years, a major goal in molecular biology has been to understand the principles of gene regulation, particularly the principles of gene transcription and translation. This is a complex matter involving the coordinated action of many proteins and nucleic acids to produce specific proteins from specific sequences of genes.

The first step in studying the structure and function of genes is to determine the gene's nucleotide sequence. DNA fingerprinting is a technique used to study the structure and function of genes and detect genetic disorders.

In the past, it was not possible to determine which traits were inherited and which were acquired through the environment. One of the most important discoveries in biology in the past decade has been discovering the molecular basis of inheritance. The discovery of the molecular basis of inheritance has transformed our understanding of the inheritance of traits profoundly influencing the study and treatment of disease. 

Another application of genomics is in the field of forensic genetics. DNA fingerprinting is a technique that uses a small section of DNA sequence, called a fingerprint, to identify an individual. DNA fingerprinting has been used extensively in identifying individuals based on their DNA patterns. It is now used in the identification of human remains, in the investigation of missing persons, in the sorting of human remains for burial, and the study of human evolution.

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  1. What is the basis of molecular inheritance?
    The theory of molecular inheritance explains how the genes we inherit from our parents are turned into the molecules that determine the traits we pass on to our children. DNA is the molecule that carries our genetic code and is the primary molecule of inheritance.

  2. What is the meaning of DNA?
    DNA is the genetic material in all living organisms. It contains the instructions needed to make a cell function, and in eukaryotes, it also contains the genetic information needed to make a whole organism work.

  3. Describe two applications of DNA fingerprinting? 
    DNA fingerprinting is a laboratory method of using DNA as a genetic fingerprint. It is used to study inheritance and is the molecular basis of forensic science that helps identify individuals by observing their unique DNA patterns.

  4. Which one is the first replicating molecule, RNA or DNA?
    The first replicating molecule is RNA

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