Molecular Basis of Inheritance

DNA and RNA are the essential genetic components responsible for passing genes from the parents to the offspring. Various traits are inherited from one generation to the next where diversity arises due to recombination. Through many studies and studies, it has been found that the genetic makeup of most living organisms is called DNA (Deoxyribonucleic Acid) and is responsible for the transmission of signals from one species to another. The molecular Basis of Inheritance is one of the most important topics in biology. The chapter carries a weightage of 12% of the total marks in NEET and 8-9% of the weightage of other entrance exams like Paramedical and Pharmacy.

Why DNA is Important to the Molecular Foundation of Inheritance?

Gene is made up of a double-stranded structure called DNA; Different parts of DNA are responsible for various factors such as skin colour, hair colour, eye color, etc. This means that DNA is largely responsible for the inheritance of cells. Some of the major reasons why DNA is important to the Molecular Foundation of Inheritance is mentioned below:

• The nucleus of a cell contains nucleolus and chromatin. This is the place where all the genes are packed.

• Chromatin is condensed into chromosomes where thousands of genes are responsible for certain traits.

• Every human being has 23 pairs of homologous chromosomes and a total of 46 pairs of chromosomes.

• Each pair of chromosomes contains thousands of genes which are responsible for deciding certain characteristics of your body as well as your personality.

• The number of chromosomes can vary from species to species.

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DNA and RNA structure

Some basic structure of DNA and RNA is discussed below:

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How is Polynucleotide Made by joining Nucleotides?

The N-glycosidic bond binds to the nitrogenous base and pentose sugar, forming a nucleoside. The phosphate group connected to this nucleoside by phosphodiester linking forms the nucleotide. Many nucleotides combine to form polynucleotides using a 3’-5 ’phosphodiester bond. This is how nucleic acid chains form in DNA or RNA. The entire procedure of how polynucleotide is made by joining nucleotide together is discussed below:

• Each nucleotide consists of a pentose sugar-phosphate group and a nitrogenous base.

• These nucleotides are linked through a phosphodiester bond between the phosphate group of 1 nucleotide and the 3’ group of sugar in another nucleotide.

• This bond is formed using a sugar-phosphate backbone which is also supported by a nitrogenous base extending the sugar units.

• Repeating the center bonding process creates a long chain of nucleotides which forms a polynucleotide like DNA or RNA.

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Double Helix DNA Structure

Watson and Crick proposed this DNA structure with a study based on X-ray DNA sequencing. It is made up of 2 polynucleotide chains, Sugar and phosphate form the backbone of the helix structure. Nitrogen bases are internal components and are bound by hydrogen bonds. Some more details about the structure of the Double Helix of DNA are discussed below:

• DNA consists of two strands of polynucleotides that are coiled with each other in a helical shape.

• Adenine is paired with Thymine and Guanine is paired with Cytosine with hydrogen bonds.

• The two DNA strands are running opposite to each other, one from 5’ to 3’ and the other from 3’ to 5’.

• The outer structure of the helix is formed by the sugar-phosphate backbone and at the same time the nitrogenous bases are inward.

• The strands are twisted to form a right-hand helix.

• There are around 10 pairs per turn.

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Human Genome Project

It was launched as an international scientific research project for determining the base pairs that make up human DNA. It includes identifying and mapping all the genes of the human genome in terms of physical features and functionalities. It has high importance in the fields of life science, medicine and biotechnology. Basic facts about the Human Genome Project are mentioned below:

• The project was started in 1990 and was completed in 2003 which was ahead of schedule.

• It mapped around 3 billion DNA base pairs and has identified around 20,000 to 25,000 human genes.

• It was an international research initiative which involved scientists from multiple countries.

• The project has advanced an understanding of genetics that led to the improvement of medicine biotechnology and disease research.

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Types of Questions Asked from Principles of Inheritance And Variation

During the preparation of the exam, there are different types of questions asked about the Principles Of Inheritance And Variation in different forms. The table given below contains the different patterns of questions asked in different exams.

Tips, Tricks, and Strategies for Molecular Basis of Inheritance

It's hard to remember everything in a single go. We made the entire problem easy. Some of the tricks regarding "Molecular Basis of Inheritance" are given below which you can use to memorize the important points.

Structure of DNA and RNA

"DOUBLE"

• D: DNA structure (double helix)

• O: Orientation (antiparallel strands)

• U: Uracil in RNA (replaces thymine)

• B: Base pairing rules (A-T, C-G in DNA; A-U, C-G in RNA)

• L: Location (DNA in the nucleus, RNA in cytoplasm)

• E: Enzymes involved in replication (e.g., DNA polymerase)

Central Dogma of Molecular Biology

"TRT: Transcription, RNA, Translation"

• T: Transcription (formation of RNA from DNA)

• R: RNA types (mRNA, tRNA, rRNA)

• T: Translation (protein synthesis using mRNA)

DNA Replication

"HERO: Helicase, Enzymes, Replication fork, Origin"

• H: Helicase (unwinds the DNA)

• E: Enzymes (e.g., DNA polymerase, primase)

• R: Replication fork (where DNA unwinds)

• O: Origin of replication (starting point for replication)

Genetic Code

"UCAG: Universal, Codons, Amino Acids, Genetic Code"

• U: Universal (genetic code is nearly the same for all organisms)

• C: Codons (triplet code of nucleotides)

• A: Amino acids (formed according to the codon)

• G: Genetic code (provides instructions for protein synthesis)

Mutations

"SILENT: Substitution, Insertion, Loss, Errors, Nonsense, Transversion"

• S: Substitution (replacement of one base)

• I: Insertion (addition of bases)

• L: Loss (deletion of bases)

• E: Errors during replication

• N: Nonsense mutation (premature stop codon)

• T: Transversion (purine to pyrimidine or vice versa)

Regulation of Gene Expression (Lac Operon)

"LACO: Lactose, Activator, Control, Operon"

• L: Lactose (induces the operon)

• A: Activator proteins (bind to promote transcription)

• C: Control genes (regulate the operon)

• O: Operon (group of genes regulated together)

Genetic Engineering Techniques

"CRISPR: Cloning, Recombinant DNA, Insertion, Sequencing, PCR, Repair"

• C: Cloning (producing identical copies)

• R: Recombinant DNA (joining DNA from different sources)

• I: Insertion (introducing DNA into cells)

• S: Sequencing (determining the order of DNA bases)

• P: PCR (amplifying DNA)

• R: Repair (using CRISPR to edit DNA)

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