Your body is made up of 50 trillion cells. Cells come in many different varieties, with many different functions, but inside, almost every cell is a nucleus, containing 99.9% of your genes, and mitochondria, containing a few more genes. All told, you’ve nearly 20,000 genes, your genes are small parts of a long molecule, called DNA, or deoxyribonucleic acid. If you lined up all of the DNA containing all of your genes, it would measure six feet long, but it’s coiled, so tightly that it fits in just one cell nucleus.

DNA is a double-stranded molecule composed of sugar, phosphate, and four different bases: adenine, thymine, cytosine, and guanine. These bases spell out the language known as the genetic code. The number and order of these four bases determine for example, whether you are a chimp, a cow, a banana, or a human. Most genes are recipes for making specific proteins, these recipes are passed down from parents to children, from generation to generation. When someone says “You have your father’s hair”, what they mean is “You appear to have inherited a gene or genes from your father that makes a protein that instructs your hair follicle cells to produce hair that curls like your father’s”, but they usually opt for the shorter version.

Genes tell a cell how to function and what traits to express. More specifically, gene regulators turn different genes on and off in different cells, to control cell function. The long molecules of DNA, containing your genes, are organized into pieces called chromosomes. Different species have different numbers of chromosomes. Humans usually have 46 chromosomes, two sets of 23, or simply 23 pairs of chromosomes. Chimpanzees have two sets of 24, or 24 pairs of chromosomes. Rhesus monkeys have 21 pairs of chromosomes. Cows have 30 pairs of chromosomes. Chickens have 39 pairs. Fruit flies have 4 pairs, and bananas have 11 pairs. So, what percentage of the DNA in your chromosomes do you share with other species? You share 93% of your DNA with Rhesus monkey, and 98.5% with our friend, chimpanzee. How about with other humans? 99.5%. So, what makes us different, from one another? Well, for one thing, SNPs.