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The genome

The is the entire genetic material of an organism. It is found in the nucleus of a cell, and is composed of a chemical called . The study of the structure and function of the genome is called .

DNA is a - a large and complex molecule. The that make it are called . DNA is made up of two strands forming a twisted ladder structure called a . The nucleotides are arranged along the DNA to form a code. This determines the characteristics of a living .

Genomes of different organisms

Genetic material for is in their . such as bacteria do not have nuclei. Their genetic material is in the cytoplasm and includes small loops of DNA called .

Genes and chromosomes

Many nucleotides form each gene. A gene is a small section of genetic code in the DNA of a chromosome. Each gene codes for a particular sequence of in order to make a specific protein. It is a unit of , and may be copied and passed on to the next generation.

This diagram shows the relationship between the cell, its nucleus, chromosomes in the nucleus, and genes.

Diagram showing a chromosome and its DNA

Scientists now know that genes only make up a small part of an organism's DNA. Most DNA - 98.5 per cent in humans - does not code for proteins. Instead, it seems to be important in controlling . This means it controls when genes are 'read' to make proteins.

The genes and non-coding DNA are mixed together in the . These are long threads of DNA, which carry the genetic code. An organism's genetic code is made up of many genes.