Genetics is a discipline of biology, the word "genetics" comes from the Ancient Greek word for origin. It is the science of heredity. This includes the study of genes, and the inheritance of variation and traits of living organisms.
In the laboratory, genetics can be studied 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.
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.
A model of a DNA molecule
Living things are made of millions of tiny self-contained components called cells. Inside of each cell are long and complex molecules called DNA. DNA stores information that tells the cells how to create that living thing. Parts of this information, the parts that control 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 control how 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 foetus 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. 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.
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- Weiling F. Weiling, F (1991). "Historical study: Johann Gregor Mendel 1822-1884". American Journal of Medical Genetics 40 (1): 1–25; discussion 26. doi:10.1002/ajmg.1320400103. PMID 1887835.
!Note - Genes rhymes with Jeans