What Is a Gene? Definition, Structure, Function, and Inheritance   Recently updated !

A gene is a segment of DNA that contains the information needed to produce a functional RNA molecule or protein. Genes are the basic units of heredity, passing genetic information from parents to offspring. They influence an organism’s characteristics, development, growth, and biological functions.

Genes are found in the genomes of living organisms and viruses. Most organisms store their genes in DNA, although some viruses have RNA genomes. In humans and other eukaryotes, most genes occur on chromosomes in the cell nucleus. Additional genes occur in mitochondria and, in plants and algae, chloroplasts.

Some genes provide instructions for making proteins, while others produce functional RNA molecules. Genes also interact with regulatory DNA sequences, cellular signals, and environmental factors. Understanding genes is fundamental to genetics, molecular biology, evolution, medicine, and biotechnology.

Key Takeaways: Gene

• A gene is a unit of heredity that contains instructions for producing a functional RNA molecule or protein.
• Genes usually consist of DNA and occupy particular locations on chromosomes. Some viruses have RNA genes.
• Protein-coding genes are expressed through transcription and translation, while noncoding RNA genes produce RNA that functions without being translated into protein.
• Gene regulation determines when, where, and how much a gene is expressed.
• Different versions of a gene, called alleles, contribute to inherited variation. Most characteristics depend on multiple genes, environmental factors, or both.
• Humans have approximately 19,000 to 20,000 protein-coding genes, along with many genes that produce noncoding RNA.
• Changes in genes and their regulation contribute to genetic diversity, evolution, and some diseases.

Why Are Genes Important?

Genes store and transmit biological information. They help explain how organisms develop, function, reproduce, and evolve.

Understanding genes is important for several reasons:

• Heredity: Genes transmit information from one generation to the next.
• Growth and development: Genes help control cell division, differentiation, and the formation of tissues and organs.
• Cell function: Gene products participate in metabolism, cell signaling, immune responses, and countless other processes.
• Evolution: Changes in genes produce heritable variation that natural selection and other evolutionary mechanisms act upon.
• Medicine: Studying genes helps identify the causes of inherited disorders, understand cancer, and develop targeted treatments.
• Agriculture: Genetic research improves crop productivity, disease resistance, nutritional value, and livestock breeding.
• Biotechnology: Scientists use genes to produce medicines, engineer organisms, and develop diagnostic tests.

The gene concept also connects molecular biology with classical genetics. It explains how the physical structure and behavior of DNA relate to the patterns of inheritance that scientists observed long before DNA was understood.

History of the Gene

The concept of a gene developed gradually as scientists investigated heredity, chromosomes, DNA, and protein synthesis. Early researchers recognized that inherited characteristics followed predictable patterns without knowing what carried the information.

Mendel and the Foundations of Genetics (1865–1866)

Gregor Mendel, an Austrian monk and scientist, performed experiments with pea plants to investigate inheritance. He presented his findings in 1865 and published them in 1866.

Mendel proposed that characteristics are controlled by discrete hereditary factors passed from parents to offspring. His experiments established the principles of segregation and independent assortment, although he did not use the word gene.

Mendel’s findings received relatively little attention until 1900, when Hugo de Vries, Carl Correns, and Erich von Tschermak independently brought his work back to scientific attention.

Chromosomes and the Naming of Genes (1900–1913)

In 1902 and 1903, Walter Sutton and Theodor Boveri independently helped establish the chromosome theory of inheritance. The behavior of chromosomes during meiosis provided a physical explanation for Mendel’s hereditary factors.

In 1909, Danish botanist Wilhelm Johannsen introduced the term gene to describe a unit of heredity. He also distinguished between the genotype, an organism’s genetic makeup, and the phenotype, its observable characteristics.

The word gene derives from a Greek root associated with birth, origin, and generation. It is related to words such as genetics, genesis, and genome.

In 1910, Thomas Hunt Morgan demonstrated that the white-eye trait in fruit flies was inherited in a sex-linked pattern, providing evidence that genes reside on chromosomes. In 1913, Alfred Sturtevant constructed the first genetic linkage map, showing the relative positions of genes on a chromosome.

Genes and Proteins (1940s)

In 1941, George Beadle and Edward Tatum studied mutations in the bread mold Neurospora crassa. Their experiments linked genes with enzymes and helped establish the one gene–one enzyme hypothesis.

This idea was later revised to one gene–one polypeptide, because not all proteins are enzymes and some proteins contain several polypeptide chains. Modern research has shown that the relationship is even more complex.

In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty demonstrated that DNA carried the hereditary information responsible for bacterial transformation. Alfred Hershey and Martha Chase provided additional evidence for DNA as genetic material in 1952.

DNA Structure and Gene Expression (1953–1960s)

In 1953, James Watson and Francis Crick proposed the double-helix structure of DNA, drawing on experimental evidence that included X-ray diffraction work by Rosalind Franklin, Raymond Gosling, and Maurice Wilkins.

The structure explained how DNA could store information and be copied.

During the following decade, scientists established major principles of gene expression. Francis Crick described the central dogma of molecular biology, which concerns the transfer of sequence information between DNA, RNA, and proteins.

In 1961, François Jacob and Jacques Monod developed a model of gene regulation based on the bacterial lac operon. That same year, Marshall Nirenberg and Heinrich Matthaei made a major breakthrough in deciphering the genetic code.

Modern Genetics and Genomics (1970s–Present)

In 1977, Richard Roberts and Phillip Sharp and their colleagues discovered that many eukaryotic genes contain interrupted sequences called introns. Their findings changed the traditional view of genes as uninterrupted stretches of protein-coding DNA.

The development of DNA sequencing, recombinant DNA technology, and polymerase chain reaction (PCR) enabled scientists to identify and manipulate individual genes.

The Human Genome Project, conducted from 1990 to 2003, produced the first essentially complete reference sequence of the human genome. In 2022, the Telomere-to-Telomere consortium published a gapless human genome assembly, filling many remaining gaps in the earlier reference.

Modern gene research includes high-throughput sequencing, RNA analysis, gene editing using CRISPR-Cas systems, and investigations of how genes interact in complex biological networks.

Gene Definition in Biology

In classical genetics, a gene is a fundamental unit of heredity that influences a characteristic and occupies a particular location on a chromosome.

In molecular biology, a gene is a sequence of nucleotides that contains information for producing a functional RNA or protein product.

These definitions describe two related aspects of the same concept:

• The classical definition emphasizes inheritance and observable traits.
• The molecular definition emphasizes DNA sequence, gene expression, and biological function.

The molecular definition is more precise for describing how genes work, but the classical definition remains useful when studying inheritance.

The boundaries of a gene are not always simple. Some genes overlap, produce several different RNA transcripts, or interact with regulatory elements located far from their coding sequences. Consequently, scientists sometimes use different criteria when identifying and counting genes.

In biology, the word gene usually refers to a hereditary sequence. In other contexts, it may occur as a person’s name or as an abbreviation. It should not be confused with gen, a shortened form of generation.

What Is a Gene Made Of?

Genes consist of nucleic acids. In cellular organisms, genes are made of DNA (deoxyribonucleic acid).

DNA is composed of repeating units called nucleotides. Each DNA nucleotide contains a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases:

• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)

The sequence of these bases stores genetic information. In double-stranded DNA, adenine pairs with thymine, while guanine pairs with cytosine.

The order of the nucleotides determines the information that a gene contains. In protein-coding genes, this information ultimately specifies the amino acid sequence of a protein. In noncoding RNA genes, the sequence determines the RNA product and contributes to its structure and function.

Some viruses use RNA rather than DNA as their genetic material. Their RNA contains uracil (U) instead of thymine.

Where Are Genes Found?

In eukaryotic cells, most genes are located on chromosomes within the nucleus. Chromosomes contain long DNA molecules associated with proteins called histones.

Humans typically have 23 pairs of nuclear chromosomes in most nucleated body cells, for a total of 46 chromosomes. These include 22 pairs of autosomes and one pair of sex chromosomes.

Eukaryotic cells may also contain genes outside the nucleus.

• Mitochondria: Human mitochondria contain a small DNA genome with 37 genes.
• Chloroplasts: Plants and algae have chloroplast DNA containing genes involved in photosynthesis and other functions.

In bacteria and archaea, genes are usually located on a main chromosome in a region called the nucleoid. Many species also contain plasmids, which are smaller DNA molecules that can carry additional genes.

Most nucleated cells in an individual’s body contain essentially the same nuclear genes, but different types of cells express different sets of genes. This allows muscle cells, nerve cells, and liver cells to perform specialized functions.

Gene vs DNA vs Chromosome vs Genome

Although closely related, these terms describe different levels of genetic organization.

A chromosome contains genes, but not all DNA on a chromosome belongs to genes. Intergenic regions, regulatory elements, repetitive sequences, and other DNA sequences also form part of the genome.

Gene Structure

A gene has different structural regions that participate in the production and regulation of its RNA or protein product.

The arrangement varies among organisms and types of genes. The following features are especially important in typical eukaryotic protein-coding genes.

Promoter

A promoter is a DNA region where the transcription machinery assembles to begin RNA synthesis. It helps determine the starting point and direction of transcription.

Promoters commonly occur upstream of the transcribed region, although their organization varies.

Exons

Exons are regions of a gene that remain in the mature RNA after splicing.

In protein-coding genes, some exon sequences specify amino acids. Other exon sequences form untranslated regions (UTRs) that are present in the RNA but are not translated into protein.

Introns

Introns are intervening sequences that are transcribed into RNA but usually removed during RNA processing.

Many eukaryotic genes contain introns. Most bacterial protein-coding genes do not.

Introns vary greatly in length and may contain sequences involved in gene regulation.

Coding Sequence

The coding sequence (CDS) is the portion of a protein-coding gene represented in mature RNA that specifies the amino acid sequence of a protein.

Translation generally begins at a start codon and ends at a stop codon. In the standard genetic code, AUG is the usual start codon in messenger RNA. Three RNA codons, UAA, UAG, and UGA, normally signal termination.

Untranslated Regions

The 5′ untranslated region (5′ UTR) occurs before the coding sequence in mature messenger RNA. The 3′ untranslated region (3′ UTR) occurs after it.

These regions can influence RNA stability, translation efficiency, and other aspects of gene expression.

Regulatory DNA Sequences

Additional regulatory elements help control gene expression:

• Enhancers increase transcription under appropriate conditions.
• Silencers reduce transcription.
• Insulators help organize or limit certain interactions between regulatory elements and genes.
• Terminators and termination signals participate in ending transcription.

Regulatory elements may be within a gene, near it, or at considerable distances from it. Not every regulatory element is considered part of the gene itself.

Types of Genes

Genes can be classified according to their products, functions, or expression patterns.

These categories overlap. For example, an essential gene may encode a regulatory protein, and a housekeeping gene may also be essential.

Protein-Coding Genes

Protein-coding genes provide instructions for making proteins. Their products include enzymes, hormones, structural proteins, membrane channels, and signaling molecules.

For example, the human HBB gene encodes beta-globin, a protein that forms part of hemoglobin in red blood cells.

Noncoding RNA Genes

Noncoding RNA genes produce RNA molecules that function without being translated into proteins.

Examples include:

• Ribosomal RNA (rRNA), which forms part of ribosomes and participates in protein synthesis.
• Transfer RNA (tRNA), which delivers amino acids during translation.
• MicroRNA (miRNA), which helps regulate gene expression.
• Small nuclear RNA (snRNA), which participates in RNA splicing.
• Long noncoding RNA (lncRNA), which can perform diverse regulatory and structural functions.

Not every RNA transcript detected in a cell necessarily has a demonstrated biological function. Scientists continue to investigate which noncoding transcripts are functional gene products.

What Do Genes Do?

The primary function of a gene is to provide information for making a functional biological product.

Genes influence numerous processes, including:

• Protein synthesis: Directing the production of proteins with structural, catalytic, and regulatory roles.
• Metabolism: Providing enzymes needed for chemical reactions and energy transformations.
• Development: Controlling processes that establish body structures and cell identities.
• Cell signaling: Producing molecules involved in communication within and between cells.
• Homeostasis: Helping maintain relatively stable internal conditions.
• DNA maintenance: Producing proteins involved in DNA replication and repair.
• Reproduction: Participating in gamete formation, fertilization, and development.
• Adaptation: Providing heritable variation that populations may use to adapt over generations.

Genes generally do not act independently. Their products interact with other molecules in pathways and networks. These interactions help explain why a single gene can influence several characteristics and why one characteristic can depend on many genes.

How Do Genes Work?

Genes work through a process called gene expression, in which genetic information is used to produce a functional RNA or protein.

For protein-coding genes, the basic flow of sequence information is:

DNA → RNA → Protein

This familiar pathway involves transcription and translation. It summarizes a major part of the central dogma of molecular biology, although biological information transfer is more complex. For example, reverse transcription transfers sequence information from RNA to DNA.

Step 1: Gene Activation

Regulatory proteins called transcription factors interact with DNA sequences and other components of the transcription machinery.

These interactions help determine whether a gene is transcribed, when transcription begins, and how much RNA is produced.

Step 2: Transcription

During transcription, an enzyme called RNA polymerase uses one strand of DNA as a template to synthesize a complementary RNA molecule.

The RNA contains information corresponding to the transcribed DNA sequence.

In eukaryotes, transcription of nuclear genes occurs in the nucleus. In bacteria, transcription occurs in the cytoplasm.

Step 3: RNA Processing

Many eukaryotic protein-coding genes initially produce precursor messenger RNA (pre-mRNA).

Before translation, the RNA generally undergoes several modifications:

• A modified cap is added to the 5′ end.
• Introns are removed and exons are joined together through splicing.
• The 3′ end is processed, typically including the addition of a poly(A) tail.

These modifications help protect the RNA, regulate its activity, and prepare it for translation.

Step 4: Translation

The mature messenger RNA moves to the cytoplasm, where ribosomes read its sequence.

Ribosomes interpret nucleotide triplets called codons. Transfer RNA molecules bring the appropriate amino acids, which are joined into a growing polypeptide chain.

The genetic code specifies which amino acid corresponds to each codon.

Step 5: Protein Folding and Function

After synthesis, the polypeptide folds into a three-dimensional structure. Some proteins also undergo chemical modifications or combine with other polypeptides.

The finished protein performs its biological function, which may involve catalyzing reactions, transporting substances, providing structural support, or regulating other processes.

Note: Noncoding RNA genes also undergo transcription, but their RNA products function without translation. Their transcripts may undergo processing before becoming functional.

Can One Gene Make More Than One Protein?

Yes. The traditional idea that one gene produces one protein is an oversimplification.

A single gene can produce several related RNA transcripts and protein forms through mechanisms such as alternative splicing, alternative transcription initiation, and alternative RNA processing.

Alternative splicing is especially important in eukaryotes. It allows a cell to join exons in different combinations, producing distinct mature RNA transcripts from the same gene.

These transcripts may encode different protein isoforms with different properties or functions.

Other mechanisms, including alternative translation initiation and certain types of RNA editing, can add further diversity.

As a result, the number of proteins that an organism can produce is not limited to its number of protein-coding genes.

Gene Regulation

Gene regulation is the process by which cells control the timing, location, and amount of gene expression.

Regulation is essential because cells must produce the correct molecules at the correct time. For example, pancreatic beta cells produce insulin, while specialized cells in the eye produce proteins involved in vision.

Although most nucleated cells contain essentially the same nuclear genes, differences in gene expression help them develop and maintain specialized functions.

Transcriptional Regulation

Transcriptional regulation determines how much RNA is produced from a gene.

Transcription factors bind DNA and interact with promoters, enhancers, and other regulatory elements. Some activate transcription, while others repress it.

In bacteria, related genes are sometimes organized into operons. An operon allows several genes to be transcribed together and regulated as a group.

The lac operon in Escherichia coli is a classic example. It regulates genes involved in lactose metabolism in response to lactose availability and other environmental conditions.

Epigenetic Regulation

Epigenetic regulation involves changes in gene activity that do not require changes in the underlying DNA sequence.

Important mechanisms include:

• DNA methylation, which can alter the accessibility or activity of DNA sequences.
• Histone modifications, which influence how DNA is packaged and accessed.
• Changes in chromatin structure, which affect interactions between DNA and regulatory proteins.

Some epigenetic states persist through cell division. However, most acquired epigenetic changes are not reliably transmitted across multiple generations.

Post-Transcriptional Regulation

Cells also regulate gene expression after RNA synthesis.

These mechanisms include alternative splicing, RNA editing, RNA transport, and RNA degradation.

MicroRNAs and other regulatory RNA molecules can reduce the stability or translation of target messenger RNAs.

Translational and Post-Translational Regulation

Cells regulate how efficiently messenger RNA is translated into proteins. They also modify proteins after synthesis.

Protein modifications, transport, and degradation influence how long proteins remain active and where they function.

Together, these processes allow gene expression to respond to developmental signals, nutrients, temperature, stress, and other conditions.

How Are Genes Inherited?

Genes pass from parents to offspring through reproduction.

In organisms that reproduce sexually, offspring typically inherit genetic material from two parents. Each parent contributes chromosomes through reproductive cells called gametes.

In humans, most body cells are diploid, meaning they contain two sets of chromosomes. Eggs and sperm are haploid, containing one set.

During fertilization, an egg and sperm combine to restore the diploid chromosome number.

Genes and Alleles

An allele is one version of a gene or genetic sequence at a particular locus.

For most genes on autosomes, a diploid organism carries two copies, one inherited from each parent. The two copies may have identical or different sequences.

An individual with two identical alleles at a locus is homozygous. An individual with two different alleles is heterozygous.

Alleles may produce different forms or amounts of a gene product, contributing to variation among individuals.

Dominant and Recessive Alleles

In simple Mendelian inheritance, alleles may exhibit dominant or recessive relationships.

• A dominant allele produces its associated phenotype when present in one copy.
• A recessive allele generally produces its associated phenotype only when a second dominant allele is absent.

Consider a hypothetical recessive condition in which A represents a typical allele and a represents a disease-associated recessive allele.

If both parents are heterozygous (Aa), their possible offspring genotypes are:

These probabilities apply to each pregnancy independently and assume a simple autosomal recessive condition with complete penetrance.

Not all inheritance follows dominant and recessive patterns. Other relationships include incomplete dominance, codominance, and more complex interactions among genes.

Other Patterns of Gene Inheritance

Genes may follow several inheritance patterns:

• Autosomal inheritance: Genes occur on chromosomes other than sex chromosomes.
• X-linked inheritance: Genes on the X chromosome show inheritance patterns influenced by sex chromosome composition.
• Y-linked inheritance: Genes on the Y chromosome typically pass from fathers to sons.
• Mitochondrial inheritance: In humans, mitochondrial DNA is normally inherited from the mother.
• Polygenic inheritance: Multiple genes influence a characteristic.

Linked genes, which are located near one another on the same chromosome, tend to be inherited together. Crossing over during meiosis can produce new combinations of alleles.

In bacteria, genes may also spread between organisms through horizontal gene transfer, including transformation, transduction, and conjugation.

Genes and Traits

Genes influence an organism’s phenotype, or observable characteristics. However, the relationship between genes and traits is often complex.

Some traits result primarily from variation in a single gene. These are called monogenic traits.

Many other traits are polygenic, meaning they involve multiple genes. Human height, for example, reflects the combined effects of numerous genetic variants as well as environmental factors such as nutrition and health.

The relationship between genotype and phenotype also involves several important concepts:

• Pleiotropy: A single gene influences multiple traits.
• Polygenic inheritance: Multiple genes contribute to one trait.
• Epistasis: The effect of a gene depends on other genes.
• Penetrance: The proportion of individuals with a particular genotype who show its associated phenotype.
• Expressivity: The degree to which a trait is expressed among individuals with a particular genotype.

These interactions explain why individuals carrying the same genetic variant do not always have identical characteristics.

Gene Mutations and Genetic Variation

A mutation is a change in a DNA sequence. The term genetic variant describes a difference in DNA sequence relative to a reference sequence or other versions.

Mutations can occur through errors during DNA replication, exposure to certain environmental agents, or other biological processes.

Common types of mutations include:

Mutations may affect a gene’s protein product, RNA product, expression level, or regulatory interactions.

Some mutations have harmful effects, some have beneficial effects in particular environments, and many have little or no detectable effect.

Mutations in reproductive cells or their precursors may be inherited by offspring. Somatic mutations arise in body cells and generally are not transmitted through sexual reproduction.

Genetic variation provides the raw material for evolution. Over generations, natural selection, genetic drift, migration, and mutation change the frequencies of alleles in populations.

Examples of Human Genes and Their Functions

Human genes perform a wide variety of functions. Several well-studied examples illustrate how gene products affect biological processes.

These examples demonstrate that genes influence characteristics through their RNA and protein products.

A gene is not inherently a “disease gene.” For example, everyone normally has a CFTR gene. Certain variants alter its function and cause disease.

What Are Essential Genes?

An essential gene is a gene required for survival, reproduction, or another specified vital function under particular conditions.

Essential genes commonly participate in fundamental cellular processes, such as:

• DNA replication and repair
• RNA synthesis and processing
• Protein synthesis
• Energy metabolism
• Cell membrane maintenance
• Cell division

Essentiality depends on the organism, cell type, developmental stage, and environment.

A gene required for survival under one set of conditions may not be essential under another. For example, a bacterium might require a particular biosynthetic gene when growing without a nutrient but not when that nutrient is supplied.

How Many Essential Genes Do Humans Have?

There is no single definitive number of essential human genes.

Genome-wide studies using CRISPR-Cas9 and other gene-disruption techniques have identified approximately 2,000 genes required for the growth or survival of various cultured human cell lines.

However, these experiments measure essentiality under specific laboratory conditions. They do not identify every gene required for human development, reproduction, or survival.

Some genes are dispensable for the survival of an isolated cell but essential for the normal function of a tissue or organism.

Essential vs Nonessential Genes

Nonessential does not mean useless.

A nonessential gene may improve an organism’s growth, reproductive success, disease resistance, or ability to survive environmental changes.

For example, a gene involved in defending against a particular pathogen may be unnecessary when the pathogen is absent but highly advantageous when it is present.

How Many Genes Do Humans Have?

Humans have approximately 19,000 to 20,000 protein-coding genes, as well as numerous genes that produce noncoding RNA.

The precise count depends on how researchers identify, classify, and annotate genes.

For example, the GENCODE human genome annotation, release 50 (June 2026), reports 19,442 protein-coding genes, excluding an additional category of readthrough genes.

The same release identifies tens of thousands of long noncoding RNA gene loci, thousands of small noncoding RNA genes, and numerous pseudogenes.

Not every annotated RNA gene has a confirmed biological function. Consequently, there is no universally accepted total for all functional human genes.

How Many Genes Does an Organism Have?

Gene counts differ widely among organisms.

Estimates vary by strain, genome assembly, and annotation method.

The number of genes does not directly measure an organism’s complexity. Some plants contain more protein-coding genes than humans, partly because of evolutionary events involving gene and genome duplication.

Complexity also depends on gene regulation, interactions between gene products, alternative splicing, and other molecular processes.

How Much of Human DNA Consists of Genes?

Only about 1–2% of human nuclear DNA directly encodes protein sequences.

However, this does not mean that the remaining DNA is useless. Genes contain noncoding regions such as introns and untranslated regions. The genome also contains regulatory elements, noncoding RNA genes, repetitive sequences, and structural regions.

Some noncoding DNA performs important functions, while the functions of other regions remain uncertain or may be absent.

What Are Pseudogenes?

A pseudogene is a DNA sequence resembling a known gene that has generally lost its original protein-coding function.

Pseudogenes may arise through gene duplication followed by mutation, reverse transcription and reinsertion of RNA-derived DNA, or the loss of function of an ancestral gene.

Historically, scientists regarded pseudogenes as inactive genetic remnants. Many are indeed nonfunctional, but some are transcribed, and certain pseudogene-derived RNAs participate in gene regulation.

Pseudogenes provide useful information about evolutionary history because they preserve evidence of past gene duplication and other genomic changes.

Genes and Evolution

Genes change over evolutionary time through mutations, gene duplication, recombination, and other processes.

A duplicated gene may retain its original function, develop a new function, or become nonfunctional. Changes in regulatory DNA can alter when and where genes are expressed.

Genes inherited from a common ancestor are called homologous genes. Scientists use similarities in gene sequences to investigate evolutionary relationships.

Two important categories of homologous genes are:

• Orthologs: Genes in different lineages that originated from a common ancestral gene through a speciation event.
• Paralogs: Genes related through gene duplication.

Conserved genes are sequences that have changed relatively little over evolutionary time. Many participate in fundamental processes, such as ribosome function or DNA replication.

Studying conserved genes helps researchers identify important biological mechanisms shared by different organisms.

How Do Scientists Study Genes?

Modern genetics uses several techniques to identify genes, determine their functions, and investigate variation.

Researchers also use model organisms such as bacteria, yeast, fruit flies, mice, and Arabidopsis thaliana to investigate how genes function.

These organisms often have well-characterized genomes and experimental tools that make genetic research more practical.

Common Misconceptions About Genes

Misconception 1: One Gene Determines One Trait

Most traits are influenced by multiple genes, environmental factors, or both.

Even a trait strongly influenced by one gene may depend on other genes for its expression.

Misconception 2: Every Gene Codes for a Protein

Many genes produce functional RNA molecules that are not translated into proteins. Examples include tRNA, rRNA, and certain regulatory RNAs.

Misconception 3: One Gene Always Produces One Protein

Alternative splicing and other mechanisms allow many genes to produce multiple RNA transcripts and protein isoforms.

Misconception 4: Genes Determine Everything About an Organism

Genes influence development and function, but environmental conditions, developmental processes, and interactions among genes also affect the phenotype.

Misconception 5: All Mutations Are Harmful

Many mutations have no measurable effect. Some are harmful, while others are beneficial under particular conditions.

Misconception 6: Dominant Genes Are Stronger or More Common

Dominance describes the relationship between alleles and their effects on a phenotype. A dominant allele is not necessarily more common, advantageous, or biologically stronger than a recessive allele.

Misconception 7: Noncoding DNA Is Junk DNA

Some noncoding DNA performs regulatory, structural, or other functions. However, not every noncoding sequence has a known or necessary function.

Misconception 8: Every Cell Uses All Its Genes

Different cell types express different sets of genes. Gene regulation allows cells with essentially the same nuclear DNA to perform specialized functions.

Misconception 9: Essential Genes Are the Same in All Organisms

Essentiality depends on an organism’s biology and environment. A gene required by one species may be absent or unnecessary in another.

Frequently Asked Questions

Is a Gene the Same as DNA?

No. DNA is the molecule that stores genetic information in cellular organisms. A gene is a particular sequence of DNA containing information for a functional RNA or protein product.

DNA also contains regions that are not genes.

Is a Gene Bigger Than a Chromosome?

No. A chromosome generally contains many genes, along with other DNA sequences. Genes are smaller regions within chromosomes.

How Long Is a Gene?

Gene lengths vary considerably. Some human genes span only a few hundred DNA base pairs, while others extend over millions of base pairs.

Gene length includes introns and other transcribed regions, not just the sequences encoding proteins.

How Many Copies of Each Gene Does a Person Have?

Most human autosomal genes occur in two copies in typical diploid cells, one inherited from each parent.

Genes on the X and Y chromosomes may have different copy numbers, and mitochondrial genes occur in multiple copies because cells contain multiple mitochondrial DNA molecules.

Gene duplications, deletions, and other genetic variations can also change copy number.

Are Genes Passed Down from Both Parents?

Yes. In typical human sexual reproduction, each parent contributes one set of nuclear chromosomes.

However, human mitochondrial DNA is normally inherited from the mother.

Can a Gene Change During a Person’s Lifetime?

Yes. DNA mutations may arise during cell division or through exposure to mutagens.

Changes in somatic cells can affect the individual but generally are not passed to offspring through sexual reproduction.

Can Genes Be Turned On and Off?

Yes. Gene regulation controls when and where genes are expressed. However, expression is not always simply on or off. Cells can also increase or decrease the amount of RNA or protein produced.

Can Scientists Change Genes?

Yes. Gene editing techniques, including CRISPR-Cas systems, allow researchers to modify DNA sequences.

These technologies have applications in biological research, biotechnology, agriculture, and medicine.

Do All Living Organisms Have Genes?

Yes. All known cellular life uses genes to store biological information. Viruses also contain genes, although viruses are not universally classified as living organisms.

What Is the Difference Between a Gene and an Allele?

A gene is a unit of genetic information. An allele is a particular version of a gene or sequence at a genetic locus.

For example, different alleles of the same gene may produce slightly different protein products or different expression levels.

Gene Glossary

Allele: One of two or more versions of a DNA sequence at a particular locus.

Chromosome: An organized DNA molecule associated with proteins and containing genes and other sequences.

Codon: A sequence of three nucleotides in messenger RNA that specifies an amino acid or translation termination signal.

Exon: A region of a gene retained in a mature RNA after splicing.

Gene expression: The process by which genetic information produces a functional RNA or protein product.

Genome: The complete genetic material of an organism or virus.

Genotype: The genetic makeup of an organism, often referring to its alleles at one or more loci.

Intron: A sequence generally removed from an RNA transcript during splicing.

Locus: The location of a gene or genetic sequence on a chromosome.

Mutation: A change in a DNA sequence.

Phenotype: The observable or measurable characteristics of an organism.

Promoter: A DNA region involved in initiating transcription.

Transcription: The synthesis of RNA using a DNA template.

Translation: The synthesis of a polypeptide using genetic information carried by messenger RNA.

References

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• Orgogozo, V.; Peluffo, A.E.; Morizot, B. (2016). “The ‘Mendelian Gene’ and the ‘Molecular Gene’: Two Relevant Concepts of Genetic Units”. Current Topics in Developmental Biology. 119: 1–26. doi:10.1016/bs.ctdb.2016.03.002
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