Simple:

How Big is a Genome?

Enormousand tiny!

The period at the end of this sentence is small. How many human genomes do you think we can fit in this period?

So if we figure out the area of the period and the area of the nucleus we can figure out how many nuclei can sit on top of a single period.

Nucleus

he quick brown fox jumps over the lazy dog

The average cell's nucleus has a diameter of about 6 micrometers.

28 square micrometers

Let's do the math!

The period is more than 2,500 times the size of a single nucleus. So if we laid a single layer of nuclei on the period, we would have 2,500 nuclei!!!

300 micrometers

6 micrometers

Almost every cell in your body contains a full copy of your genome! The entire genome is in the part of the cell called the nucleus.

70,650 square micrometers

Cell

Let's do the math! The diameter of a period in a printed book is about 0.3 millimeters, or 300 micrometers.

WOW! Each nucleus has a full copy of my genome, and 2,500 nuclei fit on a period? My genome must be tiny!

Let's take a look inside a nucleus to see how "small" your genome actually is!

1

2

Your genome is broken into 23 chromosomes. In most cells there are two copies of each chromosome.

Each chromosome is made up of a tightly packed single strand of DNA. There can be thousands of genes on a single chromosome.

To put it another way, the DNA from one cell stretched out end-to-end would be as long as 6,667 periods lined up side by side!!!

If we take all of the DNA in a single nucleus, untangle it and stretch it out end-to-end, the entire human genome is about 2 meters (6.5 feet) long!!!

In this analogy, like a book, a genome is made up of letters. The letters in a genome are called bases. A human genome has over 6 billion bases!

If the genome book has 2,300 letters on each page, the human book would be 2,608,695 pages long!!!

That is a long book.

Let's go back to the genome-as-a-book analogy to get an idea of how long your genome is.

I don't get it

What is a gene made of?

I got it!

How big is a genome?

What is a gene? (an analogy)

Okay, you could ask for help from somebody with more experience. Click the above link to start over. You could also go back to the main menu and try a different activity.

Great! Try one of the suggested pages above as your next activity.

How big is a genome?

Not quite.

Okay, you could try one more time, read everything carefully, see if a second time helps. Or go back to the main menu to try a different activity. Come back here later.

About the site: I developed geneticsalive.com as a companion website to cellsalive.com. Everything a cell does is a direct result of the genetics of that cell, whether it is a single-cell organism or part of a much larger organism. Thus, understanding the cells requires an understanding of the basis of all of their behaviors. About the author: I am a microbiologist studying microbial pathogenesis and the host immune response. My studies have included work in many pathogens including Rabies and Influenza viruses, Mycobacterium tuberculosis, Francisella tularensis, and Salmonella enterica. I currently live just outside of Philadelphia, PA, where I work as a postdoctoral fellow researching antigen processing and presentation during rabies infection. My email is always open for suggestions, corrections, or any other comments. Please feel free to contact me: geneticsalive@gmail.com