Your Genome is Like a Book
Your genome refers to all of your DNA, creating a book of information that is unique to you.
This book is written in a special
language—a code—consisting of letters and words that together tell your genetic story.
The information is organized into 23 chapters, or chromosome pairs.
The letters that make up the words in your book are called bases, with the genetic alphabet consisting of only four letters:
A, C, T, and G. There are three billion bases or letters in a human genome. These form
genetic "words" or "sentences". The words or sentences
represent your genes—the basic units of human heredity. Genes allow traits to be
passed on to subsequent generations, such as eye color, hair type, or height. There
are approximately 20,000–25,000 distinct genes in humans, distributed unevenly across
the chromosomes.
About 99.9% of these genetic words are shared, or common, among all people. This
makes sense as we all share similar biology (for example, two arms, two eyes, ten
toes). Despite these vast similarities, differences exist from person to person,
to the extent that no two people are identical (identical twins being the exception).
It is these "differences" that make you, well, you.
How do we read your genome?
DNA sequencing allows us to read the three billion letters, determine their order,
and detect changes at almost every position. When these letters change, it alters
the words and sometimes the story. Genotyping scans the genome sequence around specific
points (typically a few hundred thousand) to detect significant changes in the letters.
These natural "variations" can be associated with a trait, or in some cases correlate
to disease risk, drug metabolism response, or other aspects of heredity.
