Genetics is the science of heredity and variation in living organisms.
[1][2] Knowledge of the inheritance of characteristics has been implicitly used since prehistoric times for improving crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the mechanisms of inheritance, only began with the work of Gregor Mendel in the mid-1800s.
[3] Although he did not know the physical basis for heredity, Mendel observed that inheritance is fundamentally a discrete process with specific traits that are inherited in an independent manner — these basic units of inheritance are now called genes.
Following the rediscovery of Gregor Johann Mendel's observations in the early 1900s, research in 1910s yielded the first physical understanding of inheritance — that genes are arranged linearly along large cellular structures called chromosomes. By the 1950s it was understood that the core of a chromosome was a long molecule called DNA and genes existed as linear sections within the molecule. A single strand of DNA is a chain of four types of nucleotides; hereditary information is contained within the sequence of these nucleotides. Solved by Watson, Wilkins, and Crick in 1953, DNA's three-dimensional structure is a double-stranded helix, with the nucleotides on each strand physically matched to each other. Each strand acts as a template for synthesis of a new partner strand, providing the physical mechanism for the inheritance of information.
The sequence of nucleotides in DNA is used to produce specific sequences of amino acids, creating proteins — a correspondence known as the "genetic code". This sequence of amino acids in a protein determines how it folds into a three-dimensional structure, this structure is in turn responsible for the protein's function. Proteins are responsible for almost all functional roles in the cell. A change to DNA sequence can change a protein's structure and behavior, and this can have dramatic consequences in the cell and on the organism as a whole.
Although genetics plays a large role in determining the appearance and behavior of organisms, it is the interaction of genetics with the environment an organism experiences that determines the ultimate outcome. For example, while genes play a role in determining a person's height, the nutrition and health that person experiences in childhood also have a large effect.
|
Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. The main role of DNA molecules is the long-term storage of information and DNA is often compared to a set of blueprints, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules.
The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.
Chemically, DNA is a long polymer of simple units called nucleotides, with a backbone made of sugars and phosphate groups joined by ester bonds. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription. Most of these RNA molecules are used to synthesize proteins, but others are used directly in structures such as ribosomes and spliceosomes.
Within cells, DNA is organized into structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms such as animals, plants, and fungi store their DNA inside the cell nucleus, while in prokaryotes such as bacteria it is found in the cell's cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA, which helps control its interactions with other proteins and thereby control which genes are transcribed
|
