Genetics is a discipline of biology.[1] It is the science of heredity. This includes the study of genes, and the inheritance of variation and traits of living organisms.[2][3][4] In the laboratory, genetics proceeds by mating carefully selected organisms, and analysing their offspring. More informally, genetics is the study of how parents pass some of their characteristics to their children. It is an important part of biology, and gives the basic rules on which evolution acts.

The fact that living things inherit traits from their parents has been known since prehistoric times, and used to improve crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the process of inheritance, only began with the work of Gregor Mendel in the mid-nineteenth century.[5] Although he did not know the physical basis for heredity, Mendel observed that organisms inherit traits via discrete units of inheritance, which are now called genes.

Living things are made of millions of tiny self-contained components called cells. Inside of each cell are long and complex molecules called DNA.[6]DNA stores information that tells the cells how to create that living thing. Parts of this information that tell how to make one small part or characteristic of the living thing red hair, or blue eyes, or a tendency to be tall are known as genes.

Every cell in the same living thing has the same DNA, but only some of it is used in each cell. For instance, some genes that tell how to make parts of the liver are switched off in the brain. What genes are used can also change over time. For instance, a lot of genes are used by a child early in pregnancy that are not used later.

A living thing has two copies of each gene, one from its mother, and one from its father.[7] There can be multiple types of each gene, which give different instructions: one version might cause a person to have blue eyes, another might cause them to have brown. These different versions are known as alleles of the gene.

Since a living thing has two copies of each gene, it can have two different alleles of it at the same time. Often, one allele will be dominant, meaning that the living thing looks and acts as if it had only that one allele. The unexpressed allele is called recessive. In other cases, you end up with something in between the two possibilities. In that case, the two alleles are called co-dominant.

Most of the characteristics that you can see in a living thing have multiple genes that influence them. And many genes have multiple effects on the body, because their function will not have the same effect in each tissue. The multiple effects of a single gene is called pleiotropism. The whole set of genes is called the genotype, and the total effect of genes on the body is called the phenotype. These are key terms in genetics.

We know that man started breeding domestic animals from early times, probably before the invention of agriculture. We do not know when heredity was first appreciated as a scientific problem. The Greeks, and most obviously Aristotle, studied living things, and proposed ideas about reproduction and heredity.[8]

Probably the most important idea before Mendel was that of Charles Darwin, whose idea of pangenesis had two parts. The first, that persistent hereditary units were passed on from one generation to another, was quite right. The second was his idea that they were replenished by 'gemmules' from the somatic (body) tissues. This was entirely wrong, and plays no part in science today.[9] Darwin was right about one thing: whatever happens in evolution must happen by means of heredity, and so an accurate science of genetics is fundamental to the theory of evolution. This 'mating' between genetics and evolution took many years to organise. It resulted in the Modern evolutionary synthesis.

The basic rules of genetics were first discovered by a monk named Gregor Mendel in around 1865. For thousands of years, people had already studied how traits are inherited from parents to their children. However, Mendel's work was different because he designed his experiments very carefully.

Read this article:
Genetics - Simple English Wikipedia, the free encyclopedia

Comments are closed.