Chapter 4: Genomics

As mentioned before, a genome is all the genetic material contained in an organism, including its chromosomes, genes and DNA (deoxyribonucleic acid). Four basic elements - A, T, C, and G - make up our genes. The diversity of living organisms comes from countless different combinations of these four basic elements. The similarity between humans and other living things is especially strong when we look in detail at the genetic makeup of organisms such as the mouse, with which we share a common mammalian ancestor. For these species, both the number of genes and the way in which they are combined are very similar to ours. The closer the relationship between different species, the greater the similarity between their genes. In fact, the genetic makeup of a human is over 98 per cent the same as that of a pygmy chimpanzee. Almost  ten per cent of human genes are related to certain genes in creatures like flies and worms. So, we even share some of our genetic makeup with unlikely relatives.

Coloured X-ray of the skulls of a chimpanzee and a human

On the surface, humans seem very different from each other. Indeed, we are all unique - but we are also very much the same. Genetically speaking, the most that any two people differ from each other is only 0.1 per cent. The sequencing of the human genome has revealed the astonishing similarities that exist among all living beings, from humans to bacteria. We now know that every form of life is the product of the arrangement of A, T, C and G. Genes carry information for making all the proteins needed by an organism to function. These proteins determine, among other things, an organism's appearance, health, and sometimes behaviour. DNA is made up of  bases (nucleotides) that may be repeated millions of times throughout a genome (human genome: 3.2 billion pairs of bases). The arrangement of these bases is extremely important, and determines the kind of an organism, whether a plant, animal or a fungus. It is the countless possible arrangements of these four bases that account for the huge diversity of life on earth. Researchers study not only the human genome, but also the genomes of all kinds of creatures, from microbes to animals like mice and pigs. The more we learn about other genomes, the more we may discover about our own.

DNA filaments from a chromosome

Contrasting DNA sequences

DNA strand segment showing bases

Chromosome

The human genome is like a blueprint for creating humans. The genome contains all the information needed to create you, and to determine how the cells function throughout the whole life. Every one of the body cells, whether a heart cell, muscle cell, or nerve cell, contains a copy of the genome. Parents even pass on part of their genome to their children. Our genome is involved in every aspect of our behaviour and bodily processes - seeing, breathing, digesting, walking, talking, sleeping, even thinking.

Each individual human has a slightly different version of the human genome. But we differ by only less than one-hundredth of one per cent. The genome is necessary, but by itself is not enough to determine everything about us. Our surroundings, including physical, nutritional, social and cultural environments, also influence how we act or even how we look. In order to decode the human genome, researchers separate human DNA into manageable fragments and apply chemical processes in order to identify the sequence of the bases (A, T, C, G).

Anatomical drawing by Leonardo Da Vinci, 1507

The sequencing process is like "identifying the pieces and arranging them like pieces of a puzzle". Studying the human genome can help us learn more about the function of humans and other organisms. It may help us better understand why some people develop certain diseases, and help us develop more effective treatments.

The size of a genome differs from one organism to the next. It seems likely that a human would have much more DNA than a fly, because humans are so much larger and more complex. However, the complexity of each genome is not necessarily related to its size.

The Human Genome Project is involved in determining the exact order of the DNA bases of the entire human genome. The human genome contains more than 3.2 billion base pairs and ~21,000 genes. If our strands of DNA were stretched out in a line, the 46 chromosomes making up the human genome would extend more than six feet [close to two meters]. If the length of the 100 trillion cells could be stretched out, it would be over 113 billion miles [182 billion kilometers]. That is enough material to reach to the sun and back 610 times. The largest known genome belongs to a microscopic amoeba, Amoeba Dubia, which is closely followed in size by the lungfish and the Easter lily. Which goes to show that size isn't everything.