A term devised by August Weismann (1834-1914) for a kind of protoplasm in the nuclei of the reproductive or germ cells and tissues of the body, which constituted the hereditary material. It is thus analogous to DNA. He distinguished the germ cells from the soma or somatic cells, which make no contribution to germ plasm during …
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Geocentric perspective
Also called the ‘absolute’ frame of reference, this is one of three frames of reference languages provide to specify how something (the ‘figure’) is located with respect to something else (the ‘ground’) on the horizontal plane. In the geocentric frame of reference, the speaker uses fixed external bearings, as in “the fork is to the …
Geology
The scientific study of the composition and structure of the earth’s crust, its history, and the processes that shape it. As such, it considers the physical forces that act on the Earth, the chemistry of its constituent materials, and the biology of its past inhabitants as revealed by fossils. The word ‘geology’ was first used by …
Genre theory
Genres are text types such as romantic novels, scientific reports and so on. The theory argues that they are structured in specific ways in order to achieve specific purposes. The central importance of genre in the construction of meaning and the consequent need to control it leads to the view that it should be explicitly …
Genomics
Appearing in the 1980s, its main aim is to unravel the full DNA sequences and to provide genome mapping of a variety of species, including humans. One of its main tools in this regard is bioinformatics. It consists of two branches: structural genomics that attempts to determine the three-dimensional structures of proteins, and functional genomics dedicated …
Genotype and phenotype
A distinction first made by Wilhelm L. Johannsen (1857-1927) in 1909. Genotype is the genetic constitution of a cell or individual. When if refers to the whole organism, the term is sometimes exchanged with genome. Phenotype is the organism’s characters (structural and functional) determined by the combined influences of its genetic constitution and environment. Phenome is sometimes …
Genome
The total genetic material of any organism [i.e., in humans, the 23 pairs of chromosomes that make up the genome, together with the genes they house, and a lot of DNA that does not contribute to genes (i.e., non-coding DNA)]. More specifically, it is the entire genetic complement of a prokaryote species and the haploid …
Genetic determinism
The doctrine that our genes determine who we are at every level of organization, or that both structure and function are inherited rather than acquired through learning. According to Richard C. Lewontin, there are three varieties: ‘genetic fixity’ (i.e., parental genes determine the characters of their children), ‘innate capacity’ (i.e., in an impoverished environment all …
Genetic drift (or random walk)
Also known as the Sewell Wright effect, it involves chance fluctuations of gene frequencies in small isolated breeding populations, possibly leading to rapid evolutionary change (i.e., speciation). What is being claimed is that neutral alleles underlie most of the genetic diversity in natural populations and that they are fixated or eliminated by genetic drift. Another …
Genetic assimilation
A concept introduced by Waddington in 1953, and having many similarities with the Baldwin effect, in order to account for how a Lamarckian form of inheritance might be mimicked during biological evolution. It expresses the idea that a novel phenotype (also called a phenocopy) induced by particular environmental circumstances becomes genetically fixed in a population …