Welcome to Genetics - the study of heredity. More precisely, it is the study of how living organisms inherit characteristics or traits from their ancestors.
It has only been in the past one hundred years that we have begun to understand how information in the form of physical characteristics is transferred from parent to child.
In genetics, a feature of an organism is called a trait. Some traits are features of an organism's physical appearance, for example, a person's eye-color, height or weight. There are many other types of traits and these range from aspects of behavior to resistance to disease. Traits are often inherited, for example tall and thin people tend to have tall and thin children.
Other traits come from the interaction between inherited features and the environment. For example a child might inherit the tendency to be tall, but if there is very little food where they live and they are poorly nourished, they will still be short. The way genetics 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 family history and their lifestyle. Genetics will help to examine the dynamic between the often asked "Nature vs. Nurture" question.
Genetic information is carried by a long molecule called deoxyribonucleic acid, DNA for short. DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between the complementary bases adenine and thymine or cytosine and guanine that encodes the genetic information which is copied and inherited across generations.
Traits are carried in DNA as instructions for constructing and operating an organism. These instructions are contained in segments of DNA called genes. DNA is made of a sequence of simple units, with the order of these units spelling out instructions in the genetic code. This is similar to the orders of letters spelling out words. The organism "reads" the sequence of these units and decodes the instruction.
Not all the genes for a particular instruction are exactly the same. Different forms of one type of gene are called different alleles of that gene. As an example, one allele of a gene for hair color could carry the instruction to produce a lot of the pigment in black hair, while a different allele could give a garbled version of this instruction, so that no pigment is produced and the hair is white.
Mutations are either random or induced events that alter the sequence of a gene and can produce new or different traits. There are some exceptions to this, which will be discussed later. A new trait could be turning an allele for black hair into an allele for white hair.The appearance of new traits is important in evolution.