Genetics 101

The field of genetics is rapidly advancing and talked about often in today's news. The increased attention on genetics is not surprising given the recent accomplishments in the field, including the completion of the sequencing of the human genome in 2003 and the discovery, in 2006, that humans are more than 99% identical. Starting with these breakthroughs, genetics will continue to evolve and move out of the laboratory and into the clinic.

Your Body and DNA

Your body is made up of more than a trillion cells! These cells are organized into organs, like the lungs, and organ systems, like the respiratory system.

Despite differences between the cells that create your skin, and the cells that make up your heart, they all contain the same DNA. If you opened up a single cell and took out the DNA, you could stretch it into one thin thread that could reach the moon. That is almost 250,000 miles! In order to fit one copy of your DNA into each of your cells, the DNA must be packaged tightly into units called chromosomes.



genetics-101-types-of-chromosomes-2Each human cell contains 46 chromosomes, which are actually two sets of 23 chromosomes. We inherit one set of 23 chromosomes from our mother and one set from our father.

Types of Chromosomes

The first 22 pairs of chromosomes are numbered (chromosome 1, 2, 3, etc.). The last pair of chromosomes are called the sex chromosomes and are labeled as X or Y. If you are female, you received two copies of the X chromosome – one from each of your parents – making you "XX." If you are male, you inherited one copy of the X chromosome from your mother and one copy of the Y chromosome from your father, making you "XY."

Can you figure out if the chromosomes to the left are from a male or a female? (Answer: Male, because they have one X chromosome and one Y chromosome).











genetics-101-chromosomes-image-1Chromosomes are made up of genes. Genes provide all of the instructions for how your body works. Genes are essential for your body to function – your heart couldn't beat and your lungs couldn't breathe without them. Genes tell each cell in your body what role it will play as your body grows and develops. This way, your cells know whether to become muscles, bones, skin, or organs.

In total, we each have between 20,000 and 25,000 different genes. All of them can be found within each of the trillions of cells that are in our bodies. All of these genes together are called your genome.






Genes are made up of DNA (or deoxyribonucleic acid), which is created using four chemical compounds known as adenine (A), thymine (T), guanine (G), and cytosine (C). These four compounds can be thought of as "DNA building blocks" and are represented by the letters A, T, G, and C. The DNA molecule looks like a twisted ladder that scientists call a "double helix". The rungs of the ladder are built with pairs of these four building blocks. The DNA building blocks can only join together in a certain way. A can only pair with T; C can only pair with G.



The DNA Code

DNA is organized into a meaningful code using these building block letters. When the code is read, it is read in three letter "words" (called codons). These three letter codons make up our genes just like words make up sentences. Our body reads these gene "sentences" for instructions on how to make our cells, tissues, and organs and how to keep them functioning.


DNA showing the codons: CTA GTG CCA GTC ATC

DNA showing "sentences": CTA GTG CCA. GTC ATC.

dna code


Proteins do most of the work in cells and are required for the structure, function, and regulation of the body's tissues and organs. Genes provide the instructions to make proteins. The codons (or three letter words) that make up each gene code for the building blocks of proteins, called amino acids. There are more than 60 different codons that code for the 20 different amino acids in our bodies.

Each amino acid links to the previous one, making a large amino acid chain. Chains of amino acids make up proteins.

Amino Acids (Proline and Arginine)