The shells of individuals within the bivalve mollusk species Donax variabilis show diverse coloration and  patterning in their phenotypes.
Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes for color, and the pictures show the resultant phenotypes. This shows how multiple genotypes (BB and Bb) may yield the same phenotype (purple petals).
ABO blood groups determined through a Punnett square and displaying phenotypes and genotypes
Biston betularia morpha typica, the standard light-colored peppered moth
B.betularia morpha carbonaria, the melanic form, illustrating discontinuous variation

Set of observable characteristics or traits of an organism.

- Phenotype

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Richard Dawkins

British evolutionary biologist and author.

Dawkins in 2010
The Great Hall, Oundle School
At the University of Texas at Austin, March 2008
Lecturing on his book The God Delusion, 24 June 2006
Wearing a scarlet 'A' lapel pin, at the 34th annual conference of American Atheists (2008)
With Ariane Sherine at the Atheist Bus Campaign launch in London
Speaking at Kepler's Books, Menlo Park, California, 29 October 2006
Jayce Lewis with Richard Dawkins in Dawkins' home while working on Million (Part 2)
Receiving the Deschner Prize in Frankfurt, 12 October 2007, from Karlheinz Deschner
Dawkins accepting the Services to Humanism award at the British Humanist Association Annual Conference in 2012

With his book The Extended Phenotype (1982), he introduced into evolutionary biology the influential concept that the phenotypic effects of a gene are not necessarily limited to an organism's body, but can stretch far into the environment.

Wild type

Unlike culinary bananas, wild-type bananas have numerous large, hard seeds.

The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature.


Passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents.

Heredity of phenotypic traits: a father and son with prominent ears and crowns
DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.
Aristotle's model of inheritance. The heat/cold part is largely symmetrical, though influenced on the father's side by other factors; but the form part is not.
Table showing how the genes exchange according to segregation or independent assortment during meiosis and how this translates into Mendel's laws
An example pedigree chart of an autosomal dominant disorder.
An example pedigree chart of an autosomal recessive disorder.
An example pedigree chart of a sex-linked disorder (the gene is on the X chromosome)
Hereditary defects in enzymes are generally inherited in an autosomal fashion because there are more non-X chromosomes than X-chromosomes, and a recessive fashion because the enzymes from the unaffected genes are generally sufficient to prevent symptoms in carriers.
On the other hand, hereditary defects in structural proteins (such as osteogenesis imperfecta, Marfan's syndrome and many Ehlers–Danlos syndromes) are generally autosomal dominant, because it is enough that some components are defective to make the whole structure dysfunctional. This is a dominant-negative process, wherein a mutated gene product adversely affects the non-mutated gene product within the same cell.

The complete set of observable traits of the structure and behavior of an organism is called its phenotype.

Natural selection

Modern biology began in the nineteenth century with Charles Darwin's work on evolution by natural selection.
Aristotle considered whether different forms could have appeared, only the useful ones surviving.
Part of Thomas Malthus's table of population growth in England 1780–1810, from his Essay on the Principle of Population, 6th edition, 1826
Charles Darwin noted that pigeon fanciers had created many kinds of pigeon, such as Tumblers (1, 12), Fantails (13), and Pouters (14) by selective breeding.
Evolutionary developmental biology relates the evolution of form to the precise pattern of gene activity, here gap genes in the fruit fly, during embryonic development.
During the industrial revolution, pollution killed many lichens, leaving tree trunks dark. A dark (melanic) morph of the peppered moth largely replaced the formerly usual light morph (both shown here). Since the moths are subject to predation by birds hunting by sight, the colour change offers better camouflage against the changed background, suggesting natural selection at work.
1: directional selection: a single extreme phenotype favoured. 2, stabilizing selection: intermediate favoured over extremes. 3: disruptive selection: extremes favoured over intermediate. X-axis: phenotypic trait Y-axis: number of organisms Group A: original population Group B: after selection
Different types of selection act at each life cycle stage of a sexually reproducing organism.
The peacock's elaborate plumage is mentioned by Darwin as an example of sexual selection, and is a classic example of Fisherian runaway, driven to its conspicuous size and coloration through mate choice by females over many generations.
Selection in action: resistance to antibiotics grows though the survival of individuals less affected by the antibiotic. Their offspring inherit the resistance.

Natural selection is the differential survival and reproduction of individuals due to differences in phenotype.

Genetic diversity

Total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species.

A graphical representation of the typical human karyotype.
Varieties of maize in the office of the Russian plant geneticist Nikolai Vavilov
Photomontage of planktonic organisms.
A Tanzanian cheetah.

Genotypic and phenotypic diversity have been found in all species at the protein, DNA, and organismal levels; in nature, this diversity is nonrandom, heavily structured, and correlated with environmental variation and stress.


Change in the heritable characteristics of biological populations over successive generations.

Alfred Russel Wallace
Thomas Robert Malthus
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.
Duplication of part of a chromosome
This diagram illustrates the twofold cost of sex. If each individual were to contribute to the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) Asexual reproduction population doubles in size each generation.
Mutation followed by natural selection results in a population with darker colouration.
Simulation of genetic drift of 20 unlinked alleles in populations of 10 (top) and 100 (bottom). Drift to fixation is more rapid in the smaller population.
Homologous bones in the limbs of tetrapods. The bones of these animals have the same basic structure, but have been adapted for specific uses.
A baleen whale skeleton. Letters a and b label flipper bones, which were adapted from front leg bones, while c indicates vestigial leg bones, both suggesting an adaptation from land to sea.
Common garter snake (Thamnophis sirtalis sirtalis) has evolved resistance to the defensive substance tetrodotoxin in its amphibian prey.
The four geographic modes of speciation
Geographical isolation of finches on the Galápagos Islands produced over a dozen new species.
Tyrannosaurus rex. Non-avian dinosaurs died out in the Cretaceous–Paleogene extinction event at the end of the Cretaceous period.
The hominoids are descendants of a common ancestor.
As evolution became widely accepted in the 1870s, caricatures of Charles Darwin with an ape or monkey body symbolised evolution.

This is followed by three observable facts about living organisms: (1) traits vary among individuals with respect to their morphology, physiology and behaviour (phenotypic variation), (2) different traits confer different rates of survival and reproduction (differential fitness) and (3) traits can be passed from generation to generation (heritability of fitness).

Polymorphism (biology)

The white morph of the monarch in Hawaii is partly a result of apostatic selection.

In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species.

Gene expression

The process of transcription is carried out by RNA polymerase (RNAP), which uses DNA (black) as a template and produces RNA (blue).
Illustration of exons and introns in pre-mRNA and the formation of mature mRNA by splicing. The UTRs (in green) are non-coding parts of exons at the ends of the mRNA.
During the translation, tRNA charged with amino acid enters the ribosome and aligns with the correct mRNA triplet. Ribosome then adds amino acid to growing protein chain.
Protein before (left) and after (right) folding
The patchy colours of a tortoiseshell cat are the result of different levels of expression of pigmentation genes in different areas of the skin.
When lactose is present in a prokaryote, it acts as an inducer and inactivates the repressor so that the genes for lactose metabolism can be transcribed.
The lambda repressor transcription factor (green) binds as a dimer to major groove of DNA target (red and blue) and disables initiation of transcription. From.
In eukaryotes, DNA is organized in form of nucleosomes. Note how the DNA (blue and green) is tightly wrapped around the protein core made of histone octamer (ribbon coils), restricting access to the DNA. From.
Regulation of transcription in mammals. An active enhancer regulatory region is enabled to interact with the promoter region of its target gene by formation of a chromosome loop. This can initiate messenger RNA (mRNA) synthesis by RNA polymerase II (RNAP II) bound to the promoter at the transcription start site of the gene. The loop is stabilized by one architectural protein anchored to the enhancer and one anchored to the promoter and these proteins are joined to form a dimer (red zigzags). Specific regulatory transcription factors bind to DNA sequence motifs on the enhancer. General transcription factors bind to the promoter. When a transcription factor is activated by a signal (here indicated as phosphorylation shown by a small red star on a transcription factor on the enhancer) the enhancer is activated and can now activate its target promoter. The active enhancer is transcribed on each strand of DNA in opposite directions by bound RNAP IIs. Mediator (a complex consisting of about 26 proteins in an interacting structure) communicates regulatory signals from the enhancer DNA-bound transcription factors to the promoter.
DNA methylation is the addition of a methyl group to the DNA that happens at cytosine. The image shows a cytosine single ring base and a methyl group added on to the 5 carbon. In mammals, DNA methylation occurs almost exclusively at a cytosine that is followed by a guanine.
The identified areas of the human brain are involved in memory formation.
Neomycin is an example of a small molecule that reduces expression of all protein genes inevitably leading to cell death; it thus acts as an antibiotic.
The RNA expression profile of the GLUT4 Transporter (one of the main glucose transporters found in the human body)
In situ-hybridization of Drosophila embryos at different developmental stages for the mRNA responsible for the expression of hunchback. High intensity of blue color marks places with high hunchback mRNA quantity.
The three-dimensional structure of green fluorescent protein. The residues in the centre of the "barrel" are responsible for production of green light after exposing to higher energetic blue light. From.
Tet-ON inducible shRNA system

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect.

Phenotypic screening

A coal miner completes a screening survey for coalworker's pneumoconiosis.

Phenotypic screening is a type of screening used in biological research and drug discovery to identify substances such as small molecules, peptides, or RNAi that alter the phenotype of a cell or an organism in a desired manner.


Basic unit of heredity and a sequence of nucleotides in DNA that encodes the synthesis of a gene product, either RNA or protein.

Gregor Mendel
Fluorescent microscopy image of a human female karyotype, showing 23 pairs of chromosomes. The DNA is stained red, with regions rich in housekeeping genes further stained in green. The largest chromosomes are around 10 times the size of the smallest.
Schematic of a single-stranded RNA molecule illustrating a series of three-base codons. Each three-nucleotide codon corresponds to an amino acid when translated to protein
Protein coding genes are transcribed to an mRNA intermediate, then translated to a functional protein. RNA-coding genes are transcribed to a functional non-coding RNA.
Inheritance of a gene that has two different alleles (blue and white). The gene is located on an autosomal chromosome. The white allele is recessive to the blue allele. The probability of each outcome in the children's generation is one quarter, or 25 percent.
A sequence alignment, produced by ClustalO, of mammalian histone proteins
Evolutionary fate of duplicate genes.
Depiction of numbers of genes for representative plants (green), vertebrates (blue), invertebrates (orange), fungi (yellow), bacteria (purple), and viruses (grey). An inset on the right shows the smaller genomes expanded 100-fold area-wise.
Gene functions in the minimal genome of the synthetic organism, Syn 3.
Comparison of conventional plant breeding with transgenic and cisgenic genetic modification.

These alleles encode slightly different versions of a protein, which cause different phenotypical traits.