A genome is a data book or registry which records the past and future of living organisms.
Genome Sequencing provides the most comprehensive collection of an individual's genetic variation. We all have the same 30,000 genes in every DNA strand but we all have some spelling mistakes in some of the genes compared to one another. DNA resembles a long, twisty ladder formed by two strands of genetic material that connect to create what’s called a “double helix.” Each rung of the ladder joins together a pair of molecules called nucleotides: adenine (A), thymine (T), cytosine (C) and guanine (G). A always teams up with T, and C always pairs with G. Slight variations in the order of these pairs are what make a person unique. Some variations cause disease, and some don’t.
Genome sequencing is figuring out the order of DNA nucleotides, or bases, in a genome—the order of As, Cs, Gs, and Ts that make up an organism's DNA. The human genome is made up of over 3 billion of these genetic letters. If we put it in another way, a genome sequence is simply a very long string of letters in a puzzling language. When you read a sentence, the meaning is not just in the sequence of the letters. It is also in the words those letters make and in the grammar of the language. Similarly, the human genome is more than just its sequence. Imagine the genome as a book written without capitalization or punctuation, without breaks between words, sentences, or paragraphs, and with strings of nonsense letters scattered between and even within sentences. A passage from such a book in Science might look like this:
Actually the hidden words in the above sentences are;
Even in a familiar language it is difficult to pick out the meaning of the passage: The flowers are beautiful. And the genome is "written" in a far less familiar language, multiplying the difficulties involved in reading it.