Genes are nucleotides or polynucleotides within the DNA. These bits of protein hold the information your cells need to determine what shape you will take as you develop throughout your life. Information encoded on them is crucial to construct and regulate proteins and help them form the coherent structures that differentiate, for example, humans from amoebas.
Genes are the segments of DNA where RNA forms to translate into proteins. It is also a common term for the hereditary cause of traits or conditions, like the "obesity gene" or the "eyecolor gene." An "allele" refers to how your gene is expressed, as in the allele for the eye color of an individual being blue.
Variations within a single gene occasionally, but rarely, determine fully the genetic predisposition for a specific allele. In common study subjects like Drosophila melanogaster, single genes do often frequently control an entire allele. In more complex organisms, like humans or elephants, multiple genetic variations within gene networks are more likely to be linked to the expression of an allele. The characteristics resulting from the simple or complex interaction of a gene or group of genes is called a "phenotype," which translates roughly into "the look of a thing."
The word "gene" is from the Greek genos, which means "origin." The usage of the word can vary slightly between subdisciplines in biology and genetics, as it may refer to the physical nucleotides that make up a DNA segment or to the hereditary concept behind an individual gene, like the gene for blue eyes.
Genes are found in all creatures in base pairs. Simple organisms like mycoplasma genitalium has only 500580,000 pairs; a more complex organism like a human has about 2.3 billion base pairs encoding approximately 25,000 genes.
Web Resources On Genes
Genes and Development
Genetic Science Learning Center
Book Resources On Genes
Genes VIII by Benjamin Lewin
Molecular Biology of the Gene by James D. Watson et al