Gene Definition: Structure, Expression, Facts, Characteristics, Functions

A gene is defined as the basic unit of heredity, meaning it’s what parents pass down to their offspring. Genes are sections of DNA that contain instructions for making proteins, which help control traits and functions in the body. Genes determine features like blood type, eye colour, and even the risk of certain diseases. This topic is covered in the Class 12 chapter Molecular Basis of Inheritance in Biology.

Latest: NEET 2024 Paper Analysis and Answer Key 

Don't Miss: Most scoring concepts for NEET | NEET papers with solutions

New: NEET Syllabus 2025 for Physics, Chemistry, Biology

NEET Important PYQ & Solutions: Physics | Chemistry | Biology | NEET PYQ's (2015-24)

This Story also Contains

1. What is a Gene?
2. Gene Structure and Composition
3. Chromosomes and Genes

What is a Gene?

A gene is an elementary unit of heredity across all living organisms. It is identified as a definite arrangement of nucleotides in the sequence of DNA (or sometimes RNA) that acts as a coded blueprint for the manifestation or transmission of a hereditary trait from one generation of organisms to the next. Genes are found on chromosomes, with very different sizes, and huge differences in functions, they control everything about biological processes and features.

Genes are at the top of the hierarchy of biological functioning of living organisms. They command the making of proteins, which have very few exceptions in cells for playing essential roles. Proteins are enzymes, structural parts, and signal molecules, among others, that organize complex biochemical reactions holding life together. These proteins are encoded in genes, meaning that genes determine the phenotype of an organism, such as the colour of eyes, height, or disease sensitivity. Knowledge of genes and individual gene functions is the foundation of many scientific disciplines, including genetics, molecular biology, and medicine.

The study of genes was initiated in the middle of the 19th century with the pioneering work of Gregor Mendel, who determined principles of heredity using pea plants. Mendel's laws of inheritance were laid down for the real science of genetics. The finding of the structure of the DNA double helix by James Watson and Francis Crick in 1953 truly was the breakthrough in giving a molecular basis for the storage and transmission of genetic information. Later progress in genetic research, including the Human Genome Project, increased manyfold the understanding of gene sequences and operations in health, diseases, and evolution.

Also Read:

• MCQ Practice on Gene Interaction
• Principles of Inheritance and Variation
• Mendelian Genetics
• Molecular Basis of Inheritance

Gene Structure and Composition

The two forms of nucleic acids that encode genetic information are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA is a double helix and consists of two long chains of polymers, running anti-parallel of each other. The two strands are held together by the formation of hydrogen bonds in pairs between the bases: adenine (A), thymine (T), guanine (G), and cytosine (C). RNA acts mostly as a single polynucle. Both DNA and RNA are polynucleotides. A nucleotide is formed from a compound of a sugar molecule, a phosphate group, and a nitrogenous base.

In DNA, the nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G). RNA contains uracil (U) instead of thymine. Adenine pairs with thymine (or uracil in RNA), and cytosine pairs with guanine. These pairing rules are consistent with the way DNA is replicated and how genetic information is transcribed into RNA in the cell.

Chromosomes and Genes

Chromosomes are long, thread-like structures made of DNA and associated proteins located in the nucleus of eukaryotic cells. Each chromosome contains many genes, regulatory sequences, and other nucleotide sequences. Humans have 46 chromosomes, consisting of 22 pairs of autosomes and one pair of sex chromosomes, one member inherited from each parent. The genes themselves are located along specific segments of the chromosomes and code for proteins or RNA molecules, which in turn play a fundamental role in determining an organism's growth, appearance, and physiology.

Also Read:

Recommended Video on Gene Definition