average: (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

cell: The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Mostorganisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing. (in biology) To grow as an organism from conception through adulthood, often undergoing changes in chemistry, size, mental maturity, size or sometimes even shape.

development: (in biology) The growth of an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.

DNA: (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

egg: The unfertilized reproductive cell made by females.

embryo: The early stages of a developing organism, or animal with a backbone, consisting only one or a few cells. As an adjective, the term would be embryonic and could be used to refer to the early stages or life of a system or technology.

fraternal: Of our relating to brothers, or others with whom people develop close friendships and affection. (in genetics) The term for a type of twin birth where each baby comes from a separate fertilized egg. This is in contrast to identical twins, which result from a single fertilized egg (creating two separate but nearly identical babies).

genetic: Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

genome: The complete set of genes or genetic material in a cell or an organism. The study of this genetic inheritance housed within cells is known as genomics.

Iceland: A largely arctic nation in the North Atlantic, sitting between Greenland and the western edge of Northern Europe. Its volcanic island was settled between the late 800s and 1100 by immigrants from Norway and Celtic lands (ones governed by the Scots and Irish). It is currently home to roughly a third of a million people.

mutation: (v. mutate) Some change that occurs to a gene in an organisms DNA. Some mutations occur naturally. Others can be triggered by outside factors, such as pollution, radiation, medicines or something in the diet. A gene with this change is referred to as a mutant.

replicate: (in biology) To copy something. When viruses make new copies of themselves essentially reproducing this process is called replication.

trait: A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

Link:
Some identical twins dont have the exact same DNA - Science News for Students