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'''Genetics''' (from Ancient [[Greek]] γενετικός genetikos, “genitive” and that from γένεσις genesis, “[[origin]]”[1][2][3]), a [[discipline]] of [[biology]], is the [[science]] of [[heredity]] and variation in living [[organisms]].[4][5] The [[fact]] that living [[things]] inherit traits from their [[parents]] has been used since prehistoric times to improve crop plants and [[animals]] through [http://en.wikipedia.org/wiki/Selective_breeding selective breeding]. However, the modern science of genetics, which seeks to [[understand]] the [[process]] of inheritance, only began with the work of [http://en.wikipedia.org/wiki/Gregor_Mendel Gregor Mendel] in the mid-nineteenth century.[6] Although he did not know the physical basis for [http://en.wikipedia.org/wiki/Heredity heredity], Mendel observed that organisms inherit traits via discrete units of inheritance, which are now called genes.

Genes correspond to regions within [[DNA]], a molecule composed of a chain of four different types of [http://en.wikipedia.org/wiki/Nucleotides nucleotides]—the sequence of these nucleotides is the genetic [[information]] organisms inherit. DNA naturally occurs in a double stranded form, with nucleotides on each strand complementary to each other. Each strand can act as a template for creating a new partner strand—this is the [[physical]] [[method]] for making copies of genes that can be inherited.

The sequence of nucleotides in a gene is [[translated]] by [[cells]] to produce a chain of [http://en.wikipedia.org/wiki/Amino_acid amino acids], creating [http://en.wikipedia.org/wiki/Protein proteins]—the order of amino acids in a protein corresponds to the order of nucleotides in the gene. This [[relationship]] between nucleotide sequence and amino acid sequence is known as the genetic code. The amino acids in a protein determine how it folds into a three-[[dimensional]] shape; this [[structure]] is, in turn, responsible for the protein's [[function]]. Proteins carry out almost all the functions needed for cells to live. A [[change]] to the DNA in a gene can change a protein's amino acids, changing its shape and function: this can have a [[dramatic]] effect in the [[cell]] and on the [[organism]] as a whole.

Although genetics plays a large role in the [[appearance]] and [[behavior]] of organisms, it is the combination of genetics with what an organism [[experiences]] that determines the [[ultimate]] outcome. For example, while genes play a role in determining an organism's size, the [http://en.wikipedia.org/wiki/Nutrition nutrition] and other conditions it experiences after inception also have a large effect.[http://en.wikipedia.org/wiki/Genetics]

[[Category: Biology]]