What is DNA and the genome? What are chromosomes and genes?
23.NOV.2023
Written by Anna Sanniti
Reviewed by Wendi Gill, CGC
You probably already know a bit about DNA, or DeoxyriboNucleic Acid – the molecule shaped as the iconic double-helix. Found in almost every cell in our body, DNA carries the instructions for our bodies to function and makes each of us unique. In this article, we will learn more about DNA, plus other terms that you are likely to come across when discussing genetics.
The language of DNA
What is the genome?
What are chromosomes?
What are genes?
The language of DNA
DNA can be thought of as your body's instruction manual, written in a language using four letters, known as bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The rule is that A always pairs with T, and C always pairs with G, and these are known as base pairs[1]. DNA is made of two strands that are bound together by these base pairs, which then wind around each other like a twisted ladder.
The sequence of these base pairs, also known as the genetic code, creates the instructions for building proteins. Proteins are molecules that carry out important jobs in our bodies, such as:
digesting our food
creating new cells
supporting our immune system
building our hormones
repairing any damage to our DNA
What is the genome?
The genome is the term to describe the entire library of DNA found within a cell. Cells are the basic building blocks of all living things, and some examples of human cells include skin cells and muscle cells. Every living organism will have a genome within its cells, including animals, plants, viruses, and bacteria. The human genome contains about 3 billion base pairs[2]. Some interesting facts about our genome:
We are far more alike than we are different – we share 99.9% of our genome with other human beings, differing by only 0.1%[3].
DNA is packaged very tightly in our cells. If all the DNA in a single cell was unwound and placed end to end, it would stretch 6 feet[4]!
What are chromosomes?
You can think of chromosomes as the books within the library. Chromosomes are thread-like structures that wind up to package and store the entire genome. There are 46 chromosomes (or books), or more accurately 23 pairs[4]. We have 23 pairs because one chromosome is inherited from the mother, and the other from the father. These pairs of books, or chromosomes, will be very similar but will occasionally have some variations. The combination of the two books is what makes you unique!
What are genes?
You can think of each gene as a book chapter – each chapter provides different instructions for a process or physical characteristic in our bodies. Specifically, genes are the specific segments of DNA on chromosomes that house the instructions for creating proteins. We have roughly 20,000 protein-coding genes that are spread across our 23 chromosomes[5].
An example of a gene that you may have heard of in the news is BRCA1 – variations in this gene are known to be linked with an increased risk of developing breast, ovarian, prostate, and pancreatic cancer (also known as a genetic predisposition).
Let’s recap
DNA can be thought of as your body's instruction manual, written in a language using four letters, known as bases: adenine (A), cytosine (C), guanine (G), and thymine (T).
The genome is the entire library of DNA found within a cell.
Chromosomes are the books within the library, storing the entire genome.
Genes are short segments of DNA found on chromosomes – the chapters in the books. Each chapter provides different instructions for a process or physical characteristic in our bodies.
References
1. National Human Genome Research Institute Educational Resources. Base pair. Online: genome.gov
2. National Human Genome Research Institute Educational Resources. Genome. Online: genome.gov
3. National Human Genome Research Institute Educational Resources. DNA. Online: genome.gov
4. National Human Genome Research Institute Educational Resources. Chromosome. Online: genome.gov
5. National Human Genome Research Institute Educational Resources. Gene. Online: genome.gov