Introduction To Genetics

Introduction To Genetics

A long molecule that looks like a twisted ladder. It is made of four types of simple units and the sequence of these units carries information, just as the sequence of letters carries information on a page.

Nucleotides

They form the rungs of the DNA ladder and are the repeating units in DNA. There are four types of nucleotides (A, T, G and C) and it is the sequence of these nucleotides that carries information.

Chromosome

A package for carrying DNA in the cells. They contain a single long piece of DNA that is wound up and bunched together into a compact structure. Different species of plants and animals have different numbers and sizes of chromosomes.

Gene

A segment of DNA. Genes are like sentences made of the "letters" of the nucleotide alphabet, between them genes direct the physical development and behavior of an organism. Genes are like a recipe or instruction book, providing information that an organism needs so it can build or do something - like making an eye or a leg, or repairing a wound.

Allele

The different forms of a given gene that an organism may possess. For example, in humans, one allele of the eye-color gene produces green eyes and another allele of the eye-color gene produces brown eyes.

Genome

The complete set of genes in a particular organism.

Genetic engineering

When people change an organism by adding new genes, or deleting genes from its genome.

Mutation

An event that changes the sequence of the DNA in a gene.

This article is an accessible, non-technical introduction to the subject. For the main encyclopedia article, see Genetics.

Genetics is the study of genes, and studies what genes are and how they work. Genes are how living organisms inherit features from their ancestors; for example, children usually look like their parents because they have inherited their parents' genes. Genetics tries to identify which features are inherited, and explain how these features pass from generation to generation.

In genetics, a feature of a living thing is called a "trait". Some traits are part of an organism's physical appearance; such as a person's eye-color, height or weight. Other sorts of traits are not easily seen and include blood types or resistance to diseases. The way our genes and environment interact to produce a trait can be complicated. For example, the chances of somebody dying of cancer or heart disease seems to depend on both their genes and their lifestyle.

Genes are made from a long molecule called DNA, which is copied and inherited across generations. DNA is made of simple units that line up in a particular order within this large molecule. The order of these units carries genetic information, similar to how the order of letters on a page carries information. The language used by DNA is called the genetic code, which allows the genetic machinery to read the information in the genes in triplet sets of codons. This information is the instructions for constructing and operating a living organism.

The information within a particular gene is not always exactly the same between one organism and another, so different copies of a gene do not always give exactly the same instructions. Each unique form of a single gene is called an allele. As an example, one allele for the gene for hair color could instruct the body to produce a lot of pigment, producing black hair, while a different allele of the same gene might give garbled instructions that fail to produce any pigment, giving white hair. Mutations are random changes in genes, and can create new alleles. Mutations can also produce new traits, such as when mutations to an allele for black hair produce a new allele for white hair. This appearance of new traits is important in evolution.