gene
The word "gene" is shared by many disciplines, but in the primary sense "genes" are material things that parents pass to offspring during reproduction and through which they propagate their biological traits or characteristics.

In the primary, molecular sense, genes are segments of DNA within chromosomes. In particular, they are the subset of such DNA which cells transcribe into RNAs and translate, at least in part, into proteins.

genomics
Genomics is the study of an organism's genome and the use of the genes. It deals with the systematic use of genome information, associated with other data, to provide answers in biology, medicine, and industry.

Genomics appeared in the 1980s and took off in the 1990s with the initiation of genome projects for several species.

The related field of genetics is the study of genes and their role in inheritance.

Genomics has the potential of offering new therapeutic methods for the treatment of some diseases, as well as new diagnostic methods. Other applications are in the food and agriculture sectors.

The major tools and methods related to genomics are bioinformatics, genetic analysis, measurement of gene expression, and determination of gene function.

Comparison of genomes has resulted in some surprising biological discoveries. If a particular DNA sequence or pattern is present among many members of a clade, that sequence is said to have been conserved among the species, implying that it confers a selective advantage to the organisms. Experimental investigation of these sequences (revealed by genomic sequencing) has shown that some are transcribed into small RNA molecules, although the functions of these RNAs were not immediately apparent.

The identification of similar sequences (including many genes) in two distantly related organisms, but not in other members of one of the clades, has led to the theory that these sequences were acquired by horizontal gene transfer. This phenomenon is most prominent in thermophilic bacteria, where it seems that genes were transferred from Archaea to Eubacteria. It has also been noticed that bacterial genes exist in eukaryotic nuclear genomes and that these genes generally encode mitochondrial and plastid proteins, giving support to the endosymbiotic theory of the origin of these organelles.

The first genome to be sequenced in its entirety was that of bacteriophage FX174 (5,368 kb) in 1980.

The first free-living organism to be sequenced was that of Haemophilus influenzae (1.8Mb) in 1995, and since then genomes are being sequenced at a rapid pace. A rough draft of the human genome was completed by the Human Genome Project in early 2001 amid much fanfare.

genotype
The genotype is the specific genetic makeup (the specific genome) of an individual, usually in the form of DNA. It codes for the phenotype of that individual.

Typically, one refers to an individual's genotype with regard to a particular gene of interest and, in polyploid individuals, it refers to what combination of alleles the individual carries (see homozygous, heterozygous). Any given gene will usually cause an observable change in an organism, known as the phenotype. The terms genotype and phenotype are distinct for at least two reasons:

1. To distinguish the source of an observer's knowledge (one can know about genotype by observing DNA; one can know about phenotype by observing outward appearance of an organism).

2. Genotype and phenotype are not always directly correlated. Some genes only express a given phenotype in certain environmental conditions. Conversely, some phenotypes could be the result of multiple genotypes.

Glycolysis
Glycolysis (from Greek glyk meaning sweet and lysis meaning dissolving; also known as the Embden-Meyerhof pathway) is the initial stage of glucose metabolism and converts 1 molecule of glucose into 2 molecules of pyruvate. Glycolysis takes place within the cytosol of the cell and is completely anaerobic; that is, oxygen is not required.

Glycolysis is the only metabolic pathway common to nearly all living organisms, suggesting great antiquity; it may have originated with the first prokaryotes, 3.5 billion years ago or more.