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Oscar Hertwig

Oscar Hertwig was a German zoologist, anatomist and professor, who also wrote about the theory of evolution over 55 years after Charles Darwins The Origin of Species. Oscar Hertwig was a leader in the field of embryology. He discovered fertilizat ...

Histone

Histones are proteins found in eukaryotic cell nuclei, which package the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, the active component of chromosomes. Histones act as spools around which DN ...

Immobilized enzyme

An immobilized enzyme is an enzyme that is attached to an inert, insoluble material. This can provide a higher resistance to changes in condition such as pH or temperature.

Intron

An intron is a non-coding sequence in a gene. It is any nucleotide sequence within a gene that is removed by RNA splicing to get the final RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding ...

Lymphocyte

Lymphocytes are a type of white blood cell. They help an organism to fight infections. They occur in the immune system of all vertebrates. All lymphoctes have a large, blob-like nucleus. Lymphocytes can be divided into three main types: B cells. ...

Mutation

In biology, a mutation is a change in the genetic material. This means changes to the DNA or to the chromosomes which carry the DNA. These changes are heritable unless they have lethal effects. Mutations can happen for several reasons. It can hap ...

Nuclear membrane

The nuclear membrane is the membrane inside a cell around the nucleus. It has the genetic material and the nucleolus inside it. The membrane forms a double layer. It is connected to another group of membranes in the cell, the endoplasmic reticulu ...

Nucleolus

A nucleolus is the part of a eukaryotic cell where ribosomes are made. Seen under a microscope, the nucleolus is a dark spot inside the cells nucleus. It is made up of dense RNA and proteins. Prokaryotic cells also have ribosomes, but they dont m ...

Osmoregulation

Osmoregulation is the maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations. Kidneys play a very large role in human osmoregulation by regulating the amount of water reabsorbed from ...

Prokaryote

Prokaryotes are some of the simplest living things. They are unicellular organisms and they include two major divisions of simple living beings: bacteria, and archaea. They generally do not have a cell nucleus, nuclear membrane or cell organelles ...

RNA

RNA is an acronym for ribonucleic acid, a nucleic acid. Many different kinds are now known. RNA is physically different from DNA: DNA contains two intercoiled strands, but RNA only contains one single strand. RNA also contains different bases fro ...

Wilhelm Roux

Wilhelm Roux was a German zoologist, anatomist and pioneer of experimental embryology. For ten years he worked in Breslau now Wroclaw, becoming director of his own Institute of Embryology in 1879. He was professor at Innsbruck, Austria from 1889– ...

Sex determination

Sex determination is a process of development by which the sex of an individual is settled. Sex is a method of reproduction which is widespread among living things. It requires two individuals of the same species. Usually, the sexes are separate. ...

Signal recognition particle

The signal recognition particle is a common molecule found in cytoplasm. It is a ribonucleoprotein. It recognizes and targets specific proteins to the endoplasmic reticulum of eukaryotes and the plasma membrane of prokaryotes. When the SRP-riboso ...

Signal transduction

A signal transduction in biology is a cellular mechanism. It converts a stimulus into a response in the cell. There are two stages in this process: A second messenger transmits the signal into the cell, and a change takes place in the cell. A sig ...

Alfred Sturtevant

Alfred Henry Sturtevant was an American geneticist. Sturtevant made the first genetic map of a chromosome in 1913. In his career he worked on the fruit-fly Drosophila melanogaster with Thomas Hunt Morgan. Morgan was both a help and a hindrance to ...

Symbiosis

Symbiosis means living together. It describes close and long-term relationships between different species. The term was used by Anton de Bary in 1879, as "the living together of unlike organisms". A symbiont is an organism living in a relationshi ...

Syncytium

Syncytium is a living tissue where there are no complete cell walls or cell membranes. Syncytia have cytoplasm and many nuclei, but are not divided into separate cells.

Toll-like receptor

Toll-like receptors are proteins which act in the innate immune system and the digestive system. They are membrane-spanning, that is, they reach from the outside of the cell to the inside. TLRs recognize molecules which come from microbes. Once m ...

Transcription (genetics)

Transcription is when RNA is made from DNA. The DNA sequence is copied by a special enzyme called RNA polymerase to make a matching RNA strand. "All living things, with their myriad variations, use an almost identical microscopic machine to read ...

Transfection

Transfection is the process of deliberately introducing DNA or RNA into cells. The word is formed from transformation and infection. The term is used for: Transformation of cells or embryos with single or double-stranded RNA. This causes the buil ...

Translation (genetics)

Translation is the second part of protein biosynthesis. It is part of the process of gene expression. Before translation comes: RNA splicing by spliceosomes which remove introns, and. Formulation of the messenger RNA from exons. Transcription, wh ...

Edouard van Beneden

Edouard Joseph Marie Van Beneden, cytologist and marine biologist. He was professor of zoology at the University of Liege. He contributed to cytology and genetics by his work on the roundworm Ascaris. In this work he discovered how chromosomes co ...

August Weismann

August Friedrich Leopold Weismann was a German evolutionary biologist. Weismann is much admired today. Ernst Mayr thought he was "one of the great biologists of all time", and ranked him "the second most notable evolutionary theorist of the 19th ...

White blood cell

The job of white blood cells is to fight infections and cancer. They also remove poison, waste and damaged cells from the body. The number of white blood cells increases when a person is fighting infection or disease and decrease when a person is ...

Edmund Beecher Wilson

Edmund Beecher Wilson was a pioneering American zoologist and cell biologist. He wrote one of the most famous textbooks in the history of modern biology, The Cell.

Developmental biology

Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and morphogenesis. These are the processes which turn a zygote into an ...

Chimaera (genetics)

A chimaera or chimera is a single organism made of two kinds of genetically distinct cells. The two types of cells may come from separate fertilised eggs or zygotes. Chimeras that originate from distinct fertilised eggs fused together are called ...

Cleidoic egg

The cleidoic egg is the type of egg which reptiles and birds lay. Mammalian reproduction has evolved from laying cleidoic eggs to live birth. The cleidoic egg is sometimes called the amniotic egg, because it is characteristic of amniotes.

Evolutionary developmental biology

Evolutionary developmental biology interprets development in the light of evolution and modern genetics. It is called for short evo-devo. In On the Origin of Species 1859, Charles Darwin proposed evolution through natural selection, a theory cent ...

Gastrulation

Gastrulation is a phase early in the development of most animal embryos. In it the embryo is dramatically restructured by cell migration. Gastrulation varies in different phyla. It is followed by organogenesis, when individual organs develop with ...

Heterochrony

Heterochrony is any change in the timing of development in an animal or plant. It is a key concept in developmental biology and evolution, introduced by Ernst Haeckel in 1875. It applies to the time a trait appears in the growth of an organism, o ...

Hox gene

Hox genes are a group of related genes that determine the basic structure and orientation of animals. Hox is short for homeobox. Hox genes are critical for the proper placement of segment structures of animals during early embryonic development. ...

Identical twins

Identical twins start out as genetically identical: they have the same alleles. They are formed by a fertilised egg dividing into two separate individuals. They are always of the same sex, and are monozygotic or MZ twins. This contrasts with frat ...

Neoteny

Neoteny is a type of heterochrony where bodily development is slowed, but sexual development goes on at the same rate. This results in a sexually mature juvenile or larval form. A classic example is the Axolotl. It has often been suggested that t ...

Phenotype

The phenotype of an organism is the whole set of characters of that organism. It does not mean just what you can see on the surface. Rather, it means anything which can be made visible by suitable means. For example, blood groups are definitely a ...

Polyphenism

Polyphenism is a kind of polymorphism where different forms of an animal are caused a single genotype. The animal inherits the capability, but the environment determines which form develops. This contrasts with genetic polymorphism, where each mo ...

Precocial

Precocial in biology is a developmental strategy. It refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. It applies mainly to mammals and birds. The opposite developmental strategy is called ...

Recapitulation theory

The theory of recapitulation is often known as ontogeny recapitulates phylogeny. Etienne Serres first proposed this idea in 1824–26. In 1886 Ernst Haekel suggested that the embryonic development of an organism its ontogeny followed the same path ...

Regeneration

Regeneration means that an organism regrows a lost part, so that the original function is restored. It is a term in developmental biology. The ability to regenerate differs in different groups. Whereas newts, for example, can regenerate severed l ...

Stem cell

Stem cells are cells of the body which can divide and become differentiated. When an organism grows, stem cells specialize, and take specific functions. For instance, mature tissues like skin, muscle, blood, bone, liver, nerves, all have differen ...

Ecology

Ecology is the branch of biology that studies the biota, the environment, and their interactions. It comes from the Greek oikos = house, logos = study. Ecology is the study of ecosystems. Ecosystems describe the web or network of relations among ...

2007 Universal Forum of Cultures

The Universal Forum of Cultures Monterrey 2007 is an international civil-society event that will take place in the city of Monterrey, Mexico. It begins in September and ends in December. The Forum, as it is called often, is a global event which t ...

Adaptation

Adaptation is the evolutionary process where an organism becomes better suited to its habitat. This process takes place over many generations. It is one of the basic phenomena of biology. When people speak about adaptation, they often mean a feat ...

Animal colour

Animal colour is produced by light reflecting from an animals surface. The ways animals produce colours include pigments, chromatophores and other structures, and bioluminescence. Since sight is usually so important to animals, and is so often us ...

Anoxic event

An anoxic event is an event in which parts of the ocean have become low in oxygen below the surface levels, or when all the oxygen has gone. They may be called oceanic anoxic events or deep ocean anoxic events. Major anoxic events have happened, ...

Apex predator

Apex predators are predators with no natural predators of their own. They are at the top of their food chain. Apex predators have big effects on the animals and plants lower down the food chain. If they become extinct in an area, many changes hap ...

Aquifer

An aquifer is an underground layer where the material contains water. That can be less solid material like sand, gravel, clay or silt, but it can be rock as well, as long as the rock allows water to get in. From such layers or groundwater can be ...

Arctic ecology

Arctic ecology is the science that studies the ecology of the arctic. The arctic is all land and water north of the Arctic Circle. This area is very cold and has little rain. In the winter there is almost no sunlight. The growing season, when far ...

Biodiversity

The term biological diversity was used first by wildlife scientist and conservationist Raymond F. Dasmann in 1968, where he advocated conservation. It was widely adopted only in the 1980s. The term biodiversity first appeared in a publication in ...

Encyclopedic dictionary

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