What are genes, DNA and chromosomes?

Genetics is the study of heredity, which means the traits we inherit from our parents and the traits they inherit from their parents, etc. These characteristics are controlled by encoded information in every cell of the body.

The genetic unit consists of DNA, genes and chromosomes. Together, these units make up each person’s complete set of genetic instructions (called the genome), including the gender, appearance, and medical conditions we may face. No two people have the same genome.

This article provides a simple and clear explanation of genetics, including what genes, DNA, and chromosomes are. It also looks at genetic coding errors that can put people at risk for genetic diseases or birth defects.

What is a genome?

In the simplest terms, the genome is the complete set of genetic instructions that determine the characteristics (traits and conditions) of an organism. It consists of genes, DNA and chromosomes.

Genes are the units that carry the encoded information that determines our traits. Everyone has 20,000 to 25,000 different genes, half of which are inherited from our biological mother and half of which are inherited from our biological father.

DNA is the building block of genes. The genetic encoding of our traits is based on how these building blocks are arranged.

A chromosome is a unit of genes contained in every cell of the body. Each cell has a total of two sets of 23 chromosomes. Each set is inherited from our biological parents.

Your genome determines how your body will develop during pregnancy. It guides how you will grow, look and age. And, it will determine how the body’s cells, tissues and organs work (including when they may not work properly).

While the genome of each species is different, each organism within that species has its own unique genome. That’s why no two people are exactly alike, not even twins.


The genome is the complete set of genetic instructions consisting of DNA, genes and chromosomes. Every genome is unique.

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What is DNA?

In the simplest terms, DNA (DNA) are the building blocks of your genes.

DNA has a unique chemical code that guides your growth, development and function. Codes are determined by the arrangement of four compounds called nucleotide bases.

The four bases are:

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

The bases pair with each other—A with T and C with G—to form units called base pairs. The pairs are then connected to form what ends up looking like a spiral ladder, called a double helix.

The specific order or sequence of bases determines the instructions given to build and maintain an organism.

Human DNA consists of about 3 million such bases, 99% of which are identical to all humans. The remaining 1% is the difference between one person and another.

Almost every cell in the human body has the same DNA.


DNA is the building block of genes contained in nearly every cell. DNA is made up of four compounds called bases, which provide the encoded instructions for building and maintaining an organism. Depending on the arrangement of these bases, instructions will vary from person to person.

What is a gene?

A gene is a unit of DNA that is encoded for a specific purpose.

Some genes make proteins according to instructions. Proteins are molecules that not only make up tissues such as muscle and skin, but also play many key roles in the structure and function of the body.

Other genes are encoded to produce RNA (RNA), a molecule that converts information stored in DNA into proteins.

How your genes are coded will ultimately determine how you look and how your body functions. Everyone has two copies of each gene, one inherited from both parents.

Different versions of a gene are called alleles. For example, the alleles you inherit from your parents may determine whether you have brown eyes or blue eyes. Other alleles may cause congenital (genetic) diseases such as cystic fibrosis or Huntington’s disease, Other alleles may not cause disease but increase the risk of diseases such as cancer.

Genes make up only 1% to 5% of the human genome. The rest is made up of noncoding DNA, called junk DNA, which doesn’t make proteins but helps regulate the function of genes.


Genes are parts of a cell’s DNA that are programmed to make specific proteins. How genes are coded will determine the physical characteristics and traits of an individual. Everyone has two copies of each gene, one inherited from both parents.

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What are chromosomes?

Genes are packaged into bundles called chromosomes. Humans have 23 pairs of chromosomes, for a total of 46 individual chromosomes. Chromosomes are contained in the control center (nucleus) of nearly every cell in the body.

A pair of chromosomes, called the X and Y chromosomes, determine whether you are born male or female. Females have a pair of XX chromosomes, while males have a pair of XY chromosomes.

The other 22 pairs, called autosomes, determine the makeup of the rest of your body. Some genes in these chromosomes may be dominant or recessive.

By definition:

  • Autosomal dominant inheritance means that you only need one copy of the allele from one parent to develop a trait (such as brown eyes or Huntington’s disease).
  • Autosomal recessive inheritance means you need two copies of the allele—one from each parent—to develop a trait (such as green eyes or cystic fibrosis).


Chromosomes are made up of bundles of genes. Humans have 23 pairs of chromosomes, including one pair of sex chromosomes. The remaining 22 pairs, called autosomes, determine the makeup of the rest of the body.

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What is genetic variation?

Genes are prone to coding errors. Some mistakes do not have any significant effect on a person’s body structure or function, but some can.

Some genetic variants lead directly to defects or diseases, some of which may be apparent at birth, while others may only be seen later in life. Other variants can lead to changes in the gene pool that can affect the inheritance pattern of offspring.

There are three common types of genetic variation:

Gene mutation

A genetic mutation is a change in the DNA sequence. This is usually due to replication errors that occur when cells divide. It can also be caused by infections, chemicals or radiation that damage the genetic structure.

Inherited diseases such as sickle cell disease, Taysachs disease, and Phenylketonuria All are caused by a mutation in a gene. Radiation-induced cancers are caused by genetic changes caused by overexposure to medical or occupational radiation.

genetic recombination

Genetic recombination is the process by which segments of DNA are broken, recombined and repaired to create new alleles. Also known as “gene shuffling,” recombination occurs randomly in nature and is a normal event during cell division. The new allele is then passed from parent to offspring.

Down syndrome is an example of genetic recombination.

genetic transfer

Genetic migration is an evolutionary process in which the addition or subtraction of people in a population changes the gene pool, making certain traits less common or more common.

A theoretical example is the loss of Scottish redheads, which could lead to fewer Scottish children being born with redheads over time. On the other hand, migration of blond Scandinavians to India may have produced more blond offspring, as the migrants bred with the indigenous population.


Genetic variation can occur as a result of coding errors in the DNA sequence, such as by mutation or a naturally occurring event called genetic recombination. Genetic variation can also occur in populations due to changes in the gene pool.

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DNA is the building block of genes, which contain the coded instructions for building and maintaining the body. Genes are parts of DNA whose job is to make specific proteins that play a key role in the structure and function of the body. Chromosomes contain the units of genes passed from parents to offspring that determine the unique traits of an individual.

DNA, genes and chromosomes together make up the genome of every organism. Every organism—and every individual—has a unique genome.

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Genetics increasingly informs ways to diagnose, treat or prevent disease. Many of the tools used in medicine today are the result of a greater understanding of DNA, genes, chromosomes, and the entire human genome.

Today, genetic research has led to the development of targeted drugs that can treat cancer while doing less damage to non-cancerous cells. Genetic testing can be used to predict your likelihood of developing certain diseases so you can avoid them.

Genetic engineering has even allowed scientists to mass-produce human insulin in bacteria and create RNA vaccines, like some used to treat COVID-19.