In Augment’s notes, a marked term shows its definition when you hover or tap it, and each page ends with the terms it introduces.
333 terms from Continuity and change, each defined in a sentence or two, with the part of the syllabus where you first meet it. 117 of them are HL only, and marked.
The aminoacyl site of a ribosome, where an incoming tRNA carrying an amino acid binds by codon–anticodon pairing.
The release of hydrolytic enzymes from the acrosome of a sperm when it binds to the zona pellucida, which digest a path through the zona pellucida to the egg.
Establishing a forest, usually by planting trees, on land that has not been forested in recent times.
The proportion of incoming solar radiation reflected by a surface; snow and ice have a high albedo, while open ocean, forest and bare soil have a low albedo.
A rapid increase in the population of algae or cyanobacteria in a body of water, usually caused by an increased supply of nutrients such as nitrate and phosphate.
The proportion of all the copies of a gene in a population's gene pool that are a particular allele, expressed as a decimal between 0 and 1.
Splicing of different combinations of exons from the same pre-mRNA, so that one gene can code for several different polypeptides.
The phase of mitosis in which sister chromatids separate at the centromere and are pulled to opposite poles of the cell.
The part of the stamen that produces pollen grains containing the male gametes.
A sequence of three bases on tRNA that is complementary to a codon on mRNA and pairs with it by hydrogen bonds during translation.
A hormone made in the hypothalamus and secreted by the pituitary gland when the blood is too concentrated; it causes aquaporins to be inserted into collecting duct cells so more water is reabsorbed.
A predator at the top of a food chain that is not preyed upon by any other species as an adult.
Succession prevented from reaching the climax community by a continuing factor, often a human activity such as grazing, burning or drainage, so the community is held at an earlier stage (a plagioclimax).
Reproduction by a single parent, without the fusion of gametes, producing offspring that are genetically identical to the parent and to each other.
A gene mutation in which one base in the DNA sequence is replaced by a different base.
A tumour that grows slowly, stays in one place and does not invade neighbouring tissue or spread; it is not cancerous.
The build-up of a substance, such as a pollutant, in the tissues of an individual organism over its lifetime, because it is absorbed faster than it is broken down or excreted.
The mass of dissolved oxygen used by aerobic microorganisms to decompose the organic matter in a water sample, usually over five days at 20 °C in the dark; a high value indicates organic pollution.
The increase in the concentration of a persistent pollutant in the tissues of organisms at successively higher trophic levels of a food chain.
A pair of homologous chromosomes held together during prophase I and metaphase I of meiosis; it consists of four chromatids.
A hollow ball of cells formed about five days after fertilisation, with an outer layer (trophoblast), an inner cell mass and a fluid-filled cavity; the stage that implants in the endometrium.
The cup-shaped start of a nephron that surrounds the glomerulus; its inner wall of podocytes allows filtrate to pass into the tubule during ultrafiltration.
A graph showing the distribution of a continuous variable by its minimum, lower quartile, median, upper quartile and maximum, with outliers plotted separately.
Fat tissue whose cells contain many mitochondria with thermogenin, specialised for producing heat by uncoupled respiration; abundant in newborn babies and present in the neck of many adults.
A form of asexual reproduction, as in yeast, in which a small outgrowth of the parent cell receives a nucleus after mitosis and is separated by unequal cytokinesis.
A disease in which cells divide uncontrollably, forming malignant tumours that can invade tissues and spread; it results from mutations in genes that control cell division.
The total amount of greenhouse gases, expressed as the equivalent mass of carbon dioxide, released directly and indirectly by an activity, product, organisation or person.
The capture of carbon dioxide from the atmosphere and its long-term storage, for example in the biomass and soil of forests or in peat.
An agent that causes cancer; most carcinogens are mutagens that change genes controlling cell division.
The female part of a flower, made up of the stigma, style and ovary containing one or more ovules.
An individual who is heterozygous for a recessive allele that causes a disease, and so can pass the allele on without showing the disease.
The sequence of events between one cell division and the next, consisting of interphase (G1, S and G2), mitosis and cytokinesis.
The process by which a parent cell (mother cell) divides to form two daughter cells.
A membrane-bound structure formed at the equator of a dividing plant cell by the fusion of vesicles from the Golgi apparatus; it develops into the new plasma membranes and cell wall.
An increase in the number of cells by repeated cycles of cell growth and division by mitosis, used for growth, cell replacement and tissue repair.
A point in the cell cycle, such as the end of G1 or G2, at which the cell continues only if conditions are right, for example when DNA replication is complete.
A point where non-sister chromatids of a bivalent have crossed and exchanged sections of DNA during crossing over in prophase I.
One of the two identical DNA molecules that make up a chromosome after DNA replication; sister chromatids are held together at the centromere until anaphase.
The groove that forms around the equator of a dividing animal cell as a contractile ring of actin and myosin pulls the plasma membrane inwards during cytokinesis.
A long-term change in the average weather patterns of a region or of the whole Earth, including temperature, rainfall and extreme events; current climate change is caused mainly by human greenhouse gas emissions.
The relatively stable community that forms at the end of succession, in balance with the climate and soil of the area, and which persists until a major disturbance occurs.
The strand of DNA that is not transcribed; it has the same base sequence as the mRNA, with thymine in place of uracil. Also called the sense strand.
A pattern of inheritance in which both alleles are expressed in a heterozygote, giving a dual phenotype, for example both A and B antigens in blood group AB.
A sequence of three bases on mRNA that codes for one amino acid or acts as a start or stop signal.
The tube that receives filtrate from many nephrons and carries it through the medulla, where water is reabsorbed by osmosis to an extent controlled by ADH.
A variable that is associated with both the factor being studied and the outcome, so that it can create a misleading correlation between them.
A base or amino acid sequence that is identical or similar across a species or a group of species.
The persistence of biological structures, information and conditions over time, for example through DNA replication, inheritance, homeostasis and the stability of ecosystems.
The loss of colour in corals caused by expulsion of their symbiotic zooxanthellae, usually in response to high water temperature; prolonged bleaching leads to starvation and death of the coral.
The structure that develops from the follicle after ovulation and secretes progesterone (and oestradiol), maintaining the endometrium.
The release of enzymes from cortical granules of the egg after a sperm fuses with it, which harden the zona pellucida so that no other sperm can pass through.
The shrinkage of an animal cell, such as a red blood cell, in a hypertonic solution as it loses water by osmosis, giving it a shrivelled outline with spiky projections.
A gene-editing system in which a guide RNA directs the nuclease Cas9 to a complementary DNA sequence, where Cas9 cuts both strands so the gene can be disrupted or changed.
The transfer of pollen from the anther of one plant to the stigma of a different plant of the same species.
The exchange of sections of DNA between non-sister chromatids of a pair of homologous chromosomes during prophase I of meiosis.
A pattern of succession in which a community passes through a series of stages and then returns to an earlier stage, repeating the cycle instead of progressing to a single stable climax.
One of a family of regulatory proteins whose concentrations rise and fall during the cell cycle; a cyclin activates a cyclin-dependent kinase, allowing the cell to pass a checkpoint.
An enzyme that is active only when bound to a cyclin; it phosphorylates target proteins that trigger the next stage of the cell cycle.
The division of the cytoplasm of a parent cell between the two daughter cells, after nuclear division.
The feature of the genetic code that most amino acids are coded by more than one codon.
A gene mutation in which one or more nucleotides are removed from the base sequence of DNA.
A genetic cross that follows the inheritance of two different genes at the same time.
Describes a nucleus or cell that has two sets of chromosomes, so that each chromosome has a homologous partner (2n).
Natural selection in which individuals at one extreme of the range of a trait have the highest fitness, so the mean value of the trait in the population shifts in that direction over generations.
Natural selection in which individuals at both extremes of the range of a trait have higher fitness than intermediates, so the distribution may split into two groups.
A mixture of DNA fragments of known lengths run in one lane of a gel, used as a scale to estimate the sizes of unknown fragments.
An enzyme that joins DNA fragments, such as Okazaki fragments, by forming a phosphodiester bond between the 3′ end of one and the 5′ end of the next.
The addition of methyl groups to cytosine bases in DNA; methylation of a promoter represses transcription of the gene that follows it.
An enzyme that links free nucleotides into a new DNA strand complementary to a template strand, forming covalent phosphodiester bonds between them.
A prokaryotic enzyme that removes RNA primers from new DNA strands and replaces them with DNA nucleotides.
The main replicating enzyme in prokaryotes: it extends primers by adding nucleotides to the 3′ end of the new strand (5′ to 3′) and proofreads it.
An enzyme that builds short RNA primers complementary to the template, giving DNA polymerase III a 3′ end to extend.
Analysis of an individual’s DNA, usually the lengths of several short tandem repeat loci, to give a pattern of fragments that is almost unique to that individual.
The production of exact copies of a DNA molecule, with base sequences identical to the original, using each existing strand as a template.
An allele that has the same effect on the phenotype whether it is present in the homozygous or the heterozygous state.
A condition caused by trisomy 21, three copies of chromosome 21, usually resulting from non-disjunction during meiosis.
A state in which movement or change continues in opposite directions at equal rates, so that there is no net change; for example water entering and leaving a cell in an isotonic solution.
The exit site of a ribosome, where a tRNA that has given up its polypeptide is held briefly before it leaves.
The sequence of changes in the species composition of a community over time, in which one group of species replaces another, often ending in a relatively stable climax community.
The capacity of an ecosystem to persist over time, keeping its structure and functioning despite disturbances, either by resisting change or by returning to its previous state.
The inner lining of the uterus, rich in blood vessels, which thickens during each menstrual cycle ready for the implantation of an embryo.
The increase in the greenhouse effect caused by human activities that raise atmospheric concentrations of greenhouse gases such as carbon dioxide and methane, resulting in global warming.
A non-coding DNA sequence, often far from the gene, that binds activator proteins and increases the rate of transcription of a gene.
The development of patterns of differentiation in the cells of a multicellular organism, as the organism develops from a single unspecialised cell.
The passing on of patterns of gene expression to daughter cells or offspring by epigenetic tags, without any change in the base sequence of DNA.
A chemical group, such as a methyl group on cytosine or a methyl or acetyl group on a histone, that alters gene expression without changing the base sequence of DNA.
The study of heritable changes in gene expression that do not involve changes to the base sequence of DNA.
A line drawn through a plotted mean on a graph, extending above and below it, that shows the variability or uncertainty of the data, usually ±1 standard error or ±1 standard deviation.
The enrichment of a body of water with mineral nutrients, especially nitrate and phosphate, causing excessive growth of algae and other producers and leading to depletion of dissolved oxygen.
A section of a eukaryotic gene that remains in the mature mRNA after splicing and is usually translated.
The first generation of offspring produced by crossing two parents (the P generation).
The second generation of offspring, produced by crossing F1 individuals with each other or by self-pollination of the F1.
The fusion of a male gamete with a female gamete to form a diploid zygote.
The fluid formed in Bowman's capsule by ultrafiltration, containing water, glucose, amino acids, ions and urea at about plasma concentrations but no blood cells or plasma proteins.
The survival and reproductive potential of a genotype, measured by the number of offspring individuals with that genotype contribute to the next generation, relative to others.
Describes a plant cell whose contents no longer press against the cell wall because it has lost water, so that it has no turgor pressure; flaccid tissue is soft and limp.
A fluid-filled sac in the ovary containing a developing oocyte surrounded by follicle cells, which secrete oestradiol.
A hormone (FSH) secreted by the anterior pituitary that stimulates the development of follicles in the ovary and their secretion of oestradiol.
An insertion or deletion of a number of nucleotides that is not a multiple of three, which changes the reading frame so every codon after the mutation is altered.
The first growth phase of interphase, in which the cell grows, synthesises proteins and increases its number of organelles before DNA replication.
The second growth phase of interphase, after DNA replication, in which the cell grows further and prepares for mitosis.
A technique that separates DNA fragments (or proteins) by size by moving them through a gel in an electric field; smaller DNA fragments move further towards the positive electrode.
The deliberate alteration of the base sequence of DNA at a specific, chosen position in the genome, for example with CRISPR–Cas9.
The process by which the information in a gene is used to make a functional product, such as a polypeptide or RNA; it begins with transcription.
A technique for investigating the function of a gene by changing it so that it is inoperative, then observing the effect on the organism.
The tendency of alleles of genes on the same chromosome to be inherited together, so that they do not assort independently.
A change to the base sequence of a gene, by substitution, insertion or deletion of one or more nucleotides.
All the alleles of all the genes in an interbreeding population.
A mating between two chosen parents, used to study the inheritance of characteristics or to produce offspring with a desired combination of alleles.
Random change in allele frequencies in a population from one generation to the next, caused by chance differences in which individuals survive and reproduce; its effects are greatest in small populations.
Differences in the alleles and base sequences carried by individuals of a population or species; mutation is its original source.
The expression of only one allele of a gene, depending on whether it was inherited from the mother or the father, because epigenetic tags from one parent are not removed in the gametes.
The combination of alleles of a gene (or genes) that an organism has inherited.
A cell that gives rise to gametes, or a gamete itself; mutations in germ cells can be inherited by offspring.
The development of a seed into a seedling, starting with the uptake of water and ending when the young plant can photosynthesise.
A knot of capillaries inside Bowman's capsule, supplied by a wide afferent arteriole and drained by a narrower efferent arteriole, where blood plasma is filtered under high pressure.
A hormone secreted by the alpha cells of the islets of Langerhans when blood glucose concentration falls; it stimulates liver cells to break down glycogen to glucose and release it into the blood.
The synthesis of glycogen from glucose, carried out in liver and muscle cells and stimulated by insulin.
The hydrolysis of glycogen to glucose, carried out in liver cells when stimulated by glucagon (and in muscle cells for their own use).
The warming of the Earth's surface and lower atmosphere because greenhouse gases absorb long-wave infrared radiation emitted by the surface and re-emit some of it back towards the surface.
A gas in the atmosphere, such as water vapour, carbon dioxide, methane or nitrous oxide, that absorbs and re-emits long-wave infrared radiation, contributing to the greenhouse effect.
An RNA molecule with about 20 bases complementary to a target DNA sequence, which binds to Cas9 and directs it to cut at that sequence.
A sex-linked genetic disease in which blood clots slowly or not at all, caused by a recessive allele of an X-linked gene for a clotting factor (factor VIII or IX).
Describes a nucleus or cell that has one set of chromosomes (n), with one chromosome of each type.
The equations and , where and are the frequencies of two alleles, used to calculate allele and genotype frequencies in a population in genetic equilibrium.
The state of a population in which allele and genotype frequencies stay constant between generations, as the Hardy–Weinberg equation predicts, because there is no selection, mutation, migration or non-random mating and the population is very large.
An enzyme that unwinds the DNA double helix and separates the two strands by breaking the hydrogen bonds between complementary bases.
An organism, or a flower, that has both male and female reproductive organs and so produces both male and female gametes.
Having two different alleles of a gene, for example Rr.
A base or amino acid sequence that has remained identical or very similar over long periods of evolution, in distantly related species.
The addition or removal of chemical groups, such as methyl or acetyl groups, on amino acids in histone proteins, which changes how tightly DNA is packed and so affects transcription.
The maintenance of the internal environment of an organism within preset limits, despite fluctuations in the external environment.
Having two identical alleles of a gene, for example RR or rr.
Treatment with oestrogen, often combined with a progestogen, to replace the hormones that the ovaries stop secreting at the menopause.
A glycoprotein hormone secreted by the embryo (trophoblast) and later the placenta, which maintains the corpus luteum in early pregnancy; its presence in urine is the basis of pregnancy tests.
Describes a solution with a higher concentration of solutes than another solution, such as the cytoplasm of a cell; water moves by osmosis into it from the less concentrated solution.
Describes a solution with a lower concentration of solutes than another solution, such as the cytoplasm of a cell; water moves by osmosis out of it into the more concentrated solution.
A cylinder of ice drilled from an ice sheet or glacier, containing trapped bubbles of ancient air and other evidence from which past atmospheric gas concentrations and temperatures are measured.
The embedding of the blastocyst in the endometrium of the uterus, about 6–7 days after fertilisation.
Fertilisation of eggs by sperm outside the body, in a laboratory dish, after which one or more embryos are transferred to the uterus.
Reproduction between closely related individuals, or self-fertilisation, which increases homozygosity and decreases genetic diversity and vigour.
The point at which the plasma membrane of a plant cell is just beginning to pull away from the cell wall as the cell loses water; turgor pressure has fallen to zero.
A pattern of inheritance in which a heterozygote has a phenotype intermediate between those of the two homozygotes, for example pink flowers from red and white parents.
The random and independent distribution of the alleles of different genes into gametes, caused by the random orientation of pairs of homologous chromosomes in meiosis I.
A gene mutation in which one or more nucleotides are added to the base sequence of DNA.
Reduced sensitivity of target cells, such as liver, muscle and adipose cells, to insulin, so they take up less glucose; the physiological change underlying type 2 diabetes.
The part of the cell cycle between divisions, in which the cell grows, synthesises proteins, replicates its DNA and carries out its normal functions.
The difference between the upper quartile and the lower quartile, which measures the spread of the middle 50% of the data.
A non-coding sequence within a eukaryotic gene that is transcribed but removed from the pre-mRNA by splicing before translation.
Groups of endocrine cells in the pancreas; their beta cells secrete insulin and their alpha cells secrete glucagon in response to changes in blood glucose concentration.
Describes a solution with the same concentration of solutes as another solution, such as the cytoplasm of a cell, so that there is no net movement of water between them by osmosis.
A species that has a disproportionately large effect on the structure of its ecological community relative to its abundance; its removal causes major changes and risks ecosystem collapse.
One of a pair of organs that excrete metabolic waste such as urea and regulate the osmotic concentration of the blood by forming urine in about a million nephrons each.
A protein structure at the centromere of each chromatid to which spindle microtubules attach during nuclear division.
The new DNA strand built discontinuously, away from the replication fork, as a series of Okazaki fragments that are later joined.
Sea ice that is attached to the coast, the sea floor in shallow water or an ice shelf, so that it does not drift with winds and currents.
The loss of soluble mineral ions, such as nitrate, from soil as water drains through it, carrying them below the reach of plant roots and into groundwater and rivers.
The new DNA strand built continuously in the same direction as the replication fork moves, from a single RNA primer.
Carbon that has accumulated in the soil and biomass of an ecosystem over many years, decades or centuries, which can be released rapidly by fire or decomposition.
The particular position of a gene on a chromosome.
The hairpin part of the nephron in the medulla; its water-impermeable ascending limb actively transports sodium ions out, making the medulla concentrated so water can be reabsorbed from collecting ducts.
A hormone (LH) secreted by the anterior pituitary; a surge of LH triggers ovulation and the formation of the corpus luteum.
The bursting of a cell when its plasma membrane breaks, for example when an animal cell takes in water by osmosis in a hypotonic solution; in red blood cells it is called haemolysis.
A large piece of plastic debris, larger than 5 mm, such as a bag, bottle, packaging or fishing net, which can entangle or be swallowed by animals.
A cancerous tumour whose cells divide rapidly, invade neighbouring tissue and can spread to other parts of the body by metastasis.
The largest harvest that can be taken from a population year after year without reducing its size, obtained by keeping the population at about half its carrying capacity, where growth rate is greatest.
The middle value of a set of data arranged in order; for an even number of values, the mean of the two middle values.
Division of a diploid nucleus into four haploid nuclei by two successive divisions, producing nuclei that are genetically different from one another.
The monthly cycle of changes in the ovaries (the ovarian cycle) and the endometrium (the uterine cycle), controlled by FSH, LH, oestradiol and progesterone.
A region of undifferentiated plant cells that divide repeatedly by mitosis, producing new cells for growth.
A 1958 experiment that grew E. coli on heavy nitrogen (¹⁵N) and then light nitrogen (¹⁴N) and separated their DNA by density, showing that DNA replication is semi-conservative.
A small experimental ecosystem, enclosed in a container such as a sealed glass vessel, set up to investigate the effects of variables on a community under controlled conditions.
The phase of mitosis in which chromosomes, attached to spindle microtubules from both poles, line up on the equator of the cell.
The spread of cancer cells from a primary tumour to other parts of the body, through blood or lymph, where they form secondary tumours.
A greenhouse gas (CH₄) produced by anaerobic decomposition by methanogens, for example in ruminants, rice paddies, wetlands and landfill; per molecule it absorbs infrared radiation far more strongly than CO₂.
A piece of plastic smaller than 5 mm, either manufactured at that size or formed by the breakdown of larger plastic items.
A base substitution that changes a codon into one for a different amino acid, so one amino acid in the polypeptide is replaced.
Division of the nucleus into two genetically identical daughter nuclei, each with the same number of chromosomes as the parent nucleus.
The ratio of the number of cells in mitosis to the total number of cells in a sample of tissue, used as a measure of how fast cells are dividing.
The most frequent value, or class, in a set of data.
A species studied in depth because it is easy to keep, breed and manipulate, so that discoveries about it can be applied to other organisms.
An antibody produced by a clone of identical cells derived from a single B-lymphocyte, so all its molecules bind to the same site on one specific antigen.
A genetic cross that follows the inheritance of a single gene.
Twins that develop from a single fertilised egg that splits into two embryos, so they have identical genomes.
Messenger RNA: RNA transcribed from a gene that carries its base sequence, as codons, to the ribosomes for translation.
The existence of more than two alleles of a gene in the gene pool of a population; each individual still has only two of them.
An agent that increases the rate of mutation, such as benzo[a]pyrene, nitrosamines, mustard gas, UV light, X-rays and gamma rays.
The process by which individuals with heritable traits that make them better adapted to their environment survive and reproduce more than others, so the alleles for those traits become more common in the population over generations.
A gland at the base of a flower that secretes nectar, a sugary liquid that attracts and rewards pollinating animals.
The theory that combines Darwin's natural selection with Mendelian and population genetics, so that evolution is described as a change in allele frequencies in a population's gene pool over generations.
The functional unit of the kidney: a tubule consisting of Bowman's capsule, proximal convoluted tubule, loop of Henle and distal convoluted tubule, draining into a collecting duct.
Describes a material that cannot be broken down into simpler substances by decomposers such as bacteria and fungi, so it persists in the environment.
A DNA sequence that is not translated into a polypeptide, such as promoters, enhancers, introns, telomeres and the genes for tRNA and rRNA.
The failure of homologous chromosomes (in anaphase I) or sister chromatids (in anaphase II) to separate during meiosis, producing gametes with an extra or a missing chromosome.
A base substitution that changes a codon for an amino acid into a stop codon, so translation ends early and the polypeptide is shortened.
A sterile 0.9% w/v solution of sodium chloride in water, approximately isotonic with human blood plasma, used for intravenous fluids, washing wounds and storing tissues.
An enzyme that hydrolyses nucleic acids (DNA or RNA) by breaking the bonds between their nucleotides.
The decrease in the pH of seawater caused by absorption of atmospheric carbon dioxide, which forms carbonic acid and reduces the concentration of carbonate ions available for calcification.
A short section of DNA built discontinuously on the lagging strand during replication, each starting from its own RNA primer.
A mutated form of a proto-oncogene whose product is permanently active or overproduced, stimulating uncontrolled cell division.
The production of egg cells in the ovary; its divisions are unequal, so one cell keeps most of the cytoplasm and the others form small polar bodies.
A group of genes in a prokaryote that are transcribed together as one mRNA from a single promoter, under the control of one operator.
A specific base sequence at which DNA replication begins; prokaryotes usually have one per chromosome, eukaryotes many.
The total concentration of all solute particles (molecules and ions) in a solution, measured in osmoles or milliosmoles per litre (mOsm/L); osmolality is measured per kilogram of water.
A receptor cell in the hypothalamus that detects the osmotic concentration of the blood and causes ADH secretion to change.
The control of the osmotic concentration (water and solute content) of the blood and other body fluids; in mammals, mainly by the kidneys.
A value that lies unusually far from the rest of the data; in a box-and-whisker plot, more than 1.5 × IQR above the upper quartile or below the lower quartile.
The part of the menstrual cycle that takes place in the ovary: development of a follicle, ovulation, and formation and breakdown of the corpus luteum.
One of the two female gonads, containing follicles in which eggs develop; it releases eggs at ovulation and secretes oestradiol and progesterone.
The production by organisms of more offspring than the environment can support, so that many die before they reproduce.
The tube that collects the egg released from the ovary and carries it to the uterus; the usual site of fertilisation. Also called the fallopian tube.
The release of an egg (secondary oocyte) from a mature follicle in the ovary, triggered by a surge in LH.
The structure inside the ovary of a flower that contains the female gamete (egg cell) and develops into a seed after fertilisation.
A hormone secreted by the posterior pituitary that stimulates contraction of the muscle of the uterus during childbirth; its secretion increases by positive feedback.
The parental generation in a series of genetic crosses: the two individuals (often pure-breeding) crossed first.
The peptidyl site of a ribosome, which holds the tRNA carrying the growing polypeptide chain.
A diagram that shows the occurrence of a characteristic in the members of a family over several generations, used to deduce its pattern of inheritance.
Ground, including soil and rock, that has remained frozen for at least two consecutive years; in the Arctic it often contains large stores of undecomposed organic matter.
A loss of synchrony between the timing of life-cycle events in interacting species, such as a consumer's breeding and the peak of its food supply, often because they respond to different cues.
The study of the timing of recurring biological events, such as flowering, budburst, bud set, migration and breeding, and of how they are influenced by variables such as photoperiod and temperature.
The observable characteristics of an organism, resulting from its genotype and the effects of the environment.
The capacity of an organism to develop traits suited to its environment by changing patterns of gene expression, without any change in its genotype.
An inherited disease caused by a recessive allele of the gene for phenylalanine hydroxylase, so phenylalanine cannot be converted to tyrosine and builds up in the blood.
The length of the period of light in each 24-hour day, which organisms use as a cue to time seasonal events such as flowering, migration and breeding.
The first organisms to colonise bare ground in primary succession; they tolerate harsh conditions and begin soil formation, for example lichens and mosses on bare rock.
The organ formed from fetal and maternal tissue in the uterus, through which substances are exchanged between the blood of the mother and the fetus without the two bloods mixing.
The shrinking of the protoplast of a plant cell away from its cell wall when the cell loses water by osmosis in a hypertonic solution.
A change to a single base in the base sequence of DNA, such as the substitution of one base for another.
A small haploid cell, with very little cytoplasm, formed by the unequal division of the cytoplasm in meiosis I and meiosis II of oogenesis; it usually degenerates.
A small structure produced in the anther of a flower, with a tough outer wall, that contains the male gametes.
A tube that grows from a pollen grain on the stigma, through the style to an ovule, and carries the male gametes to the egg cell.
The transfer of pollen from an anther to a stigma.
A chain of adenine nucleotides added to the 3′ end of eukaryotic pre-mRNA, which protects the mRNA from breakdown.
The inheritance of a characteristic that is controlled by two or more genes, each with a small additive effect, which gives continuous variation.
A technique that amplifies a chosen DNA sequence by repeated cycles of denaturation, primer annealing and extension, doubling the number of copies in each cycle.
The fertilisation of an egg by more than one sperm, which produces an embryo with too many sets of chromosomes.
Changes made to a eukaryotic pre-mRNA before translation: removal of introns and splicing of exons, and addition of a 5′ cap and a 3′ poly-A tail.
Changes made to a polypeptide after translation, such as removal of amino acids, cutting of the chain, glycosylation or forming disulfide bonds, that make it functional.
The component of water potential due to hydrostatic pressure on water; positive under pressure, as in a turgid plant cell, and negative under tension, as in xylem (symbol Ψp).
Succession that begins in an area with no soil and no previous community, such as bare rock, a new volcanic island or ground exposed by a retreating glacier.
The tumour that forms first, at the site in the body where a cancer began.
A short single strand of nucleic acid that pairs with a complementary sequence on a template and provides a 3′ end from which DNA polymerase can start building a new strand.
A steroid hormone secreted by the corpus luteum and later the placenta that maintains the endometrium and inhibits FSH and LH secretion.
A base sequence of DNA just upstream of a gene, where RNA polymerase binds, with transcription factors, to start transcription.
Checking of a new DNA strand by DNA polymerase III, which removes a nucleotide with a mismatched base from the 3′ end and replaces it with a correctly paired one.
The first phase of mitosis, in which chromosomes condense, the spindle forms and the nuclear membrane breaks down.
A large protein complex that breaks down unneeded or damaged proteins, tagged with ubiquitin, into short peptides, allowing their amino acids to be reused.
The complete set of proteins produced by a cell, tissue or organism at a particular time.
A normal gene whose product stimulates cell division, such as a growth factor receptor; a mutation can convert it into an oncogene.
The coiled part of the nephron after Bowman's capsule, lined with cells with microvilli and many mitochondria, where all glucose and amino acids and most ions and water are reabsorbed.
The period of development during which the reproductive organs mature and secondary sexual characteristics appear, caused by rising secretion of GnRH, LH, FSH and the steroid sex hormones.
A table that shows all the possible combinations of gametes from two parents, used to predict the genotypes and phenotypes of their offspring and their expected ratios.
The independent and random alignment of each bivalent on the equator in metaphase I, which gives 2ⁿ possible combinations of chromosomes in the gametes.
An experiment in which participants are assigned at random to a treatment group or a control (placebo) group, so that differences in outcome can be attributed to the treatment.
A change in the geographical distribution of a species, for example towards the poles or to higher altitudes, as the area with suitable conditions moves because of climate change.
An allele that affects the phenotype only in the homozygous state, when no dominant allele is present.
A gamete or offspring with a new combination of alleles, not present in either of the combinations inherited by its parent, produced by independent assortment or by crossing over.
Re-establishing forest on land from which it was recently cleared, either by planting trees or by allowing natural regeneration from seeds and roots.
The Y-shaped region where the DNA double helix is being unwound and separated by helicase, so that both strands can act as templates.
A protein that binds to a specific base sequence in DNA, such as an operator or silencer, and prevents or reduces the transcription of genes.
Ecological restoration that re-establishes natural processes in an ecosystem, for example by reintroducing apex predators and keystone species, reconnecting habitats and reducing human impact, so the ecosystem becomes self-sustaining.
The enzyme that unwinds DNA, separates the strands and links RNA nucleotides into a strand complementary to the template strand during transcription.
Ribosomal RNA: RNA that, with proteins, forms the two subunits of ribosomes and catalyses the formation of peptide bonds.
The synthesis phase of interphase, in which DNA is replicated so that each chromosome comes to consist of two sister chromatids.
A base substitution that changes a codon into another codon for the same amino acid, so the polypeptide is unchanged; also called a silent mutation.
Ice that forms when seawater freezes, including drifting pack ice and landfast ice; it is a habitat for breeding, resting and feeding in polar regions.
Succession that occurs where an existing community has been disturbed or removed but the soil remains, for example after a fire or on abandoned farmland.
A tumour formed in another part of the body by cancer cells that have spread from a primary tumour.
A structure that develops from a fertilised ovule, containing an embryo plant and a food store inside a protective seed coat (testa).
The spread of seeds away from the parent plant by wind, water, animals or explosive release, which reduces competition and allows colonisation of new areas.
The separation of the two alleles of a gene into different gametes, caused by the separation of homologous chromosomes in meiosis I.
A factor in the environment, biotic or abiotic, that affects the survival or reproduction of individuals differently according to their traits, and so causes natural selection.
The reabsorption of useful substances, such as glucose, amino acids, ions and water, from the filtrate back into the blood, mainly in the proximal convoluted tubule, while waste remains in the filtrate.
A genetic mechanism that prevents fertilisation by pollen from the same plant (or a plant with the same S-allele), so male and female gametes come from different plants.
The transfer of pollen from an anther to a stigma of the same flower or of another flower on the same plant.
Replication in which each new DNA molecule consists of one strand from the original molecule and one newly built strand.
The value of a regulated variable that homeostasis maintains, such as a core body temperature of about 37 °C; the variable fluctuates within a narrow range around it.
The pattern of inheritance of a gene carried on a sex chromosome (usually the X chromosome), which differs between males and females.
Reproduction in which two gametes, usually from two different parents, fuse to form a zygote, producing offspring with new combinations of alleles.
Selection for physical or behavioural traits that increase an individual's success in attracting or competing for mates, so that the alleles for those traits become more common.
Rapid, involuntary contraction and relaxation of skeletal muscles, stimulated by the hypothalamus when the body is cold; the respiration supplying ATP for contraction releases heat.
A region of DNA in which a short base sequence (typically 2–6 bases) is repeated many times in a row; the number of repeats varies between individuals.
An inherited disease caused by a base substitution in the β-globin gene that replaces glutamic acid with valine, so haemoglobin forms fibres and red blood cells become sickle-shaped.
A base sequence in DNA that reduces the transcription of a gene when a repressor protein binds to it.
The removal of soil, especially fertile topsoil, by wind or water faster than new soil forms, often after the vegetation that protects it has been cleared.
The component of water potential due to dissolved solutes; zero for pure water and more negative as solute concentration increases (symbol Ψs).
Any body cell other than a germ cell; mutations in somatic cells are not passed to offspring but can cause cancer.
The production of sperm in the seminiferous tubules of the testes by mitosis, cell growth, two divisions of meiosis and differentiation.
An array of microtubules that forms during nuclear division, attaches to chromosomes at their centromeres and moves chromosomes or chromatids to opposite poles.
The removal of introns from pre-mRNA and the joining of exons to form mature mRNA.
Natural selection in which individuals with intermediate values of a trait have the highest fitness and both extremes are selected against, so variation decreases while the mean stays the same.
The male part of a flower, made of an anther held on a stalk called the filament.
The standard error of the mean: an estimate of how far a sample mean is likely to be from the true mean, equal to the standard deviation divided by the square root of the number of measurements.
The codon AUG, which signals the start of translation and codes for methionine.
The sticky tip of the carpel that receives pollen during pollination.
One of the three codons UAA, UAG and UGA, which code for no amino acid and signal the end of translation.
The repeated coiling of DNA and its histones into more and more compact structures, which condenses chromosomes before nuclear division.
The development of many follicles at the same time, caused by artificially high doses of FSH, so that several eggs can be collected in one cycle.
Removing organisms from a natural population at a rate no greater than the rate at which the population replaces them by reproduction and growth, so that harvesting can continue indefinitely.
The secretion of a watery salt solution by sweat glands onto the skin surface; evaporation of the water removes heat from the skin and cools the body.
A heat-stable DNA polymerase from the thermophilic bacterium Thermus aquaticus, used in PCR because it is not denatured at about 95 °C.
The last phase of mitosis, in which chromosomes reach the poles and uncoil and a nuclear membrane forms around each group.
The strand of DNA that is transcribed; the mRNA made from it has a complementary base sequence. Also called the antisense strand.
A cross between an individual of unknown genotype (or a heterozygote) and a homozygous recessive individual, so that the offspring phenotypes show the alleles in the gametes of the first individual.
One of the two male gonads, held in the scrotum, which produces sperm in its seminiferous tubules and secretes testosterone.
An organism that lives and grows best at high temperatures, typically above 45 °C, such as Thermus aquaticus in hot springs.
A sensory receptor that detects temperature; peripheral thermoreceptors in the skin and central thermoreceptors in the hypothalamus send information to the hypothalamus.
The maintenance of body temperature within narrow limits by negative feedback, balancing heat gained from metabolism and the surroundings with heat lost to the surroundings.
Two adjacent thymines on the same DNA strand joined by covalent bonds after absorbing UV radiation; the dimer distorts the helix and can cause errors in replication.
An iodine-containing hormone secreted by the thyroid gland, under control of the hypothalamus and pituitary gland, that raises the metabolic rate of body cells and so increases heat production.
A critical threshold at which a small additional change pushes an ecosystem into a different state, which is often self-sustaining and difficult or impossible to reverse.
The synthesis of RNA using a DNA strand as a template, carried out by RNA polymerase.
A protein that binds to a specific DNA sequence, such as a promoter, and helps or prevents the binding of RNA polymerase, controlling transcription of a gene.
The complete set of RNA molecules transcribed from the genome in a cell at a particular time.
The synthesis of a polypeptide on a ribosome, with an amino acid sequence determined by the codons of mRNA.
Transfer RNA: a folded RNA molecule with an anticodon at one end and a specific amino acid attached at its 3′ end, which it brings to the ribosome.
An abnormal mass of tissue formed by uncontrolled cell division.
A gene whose product restrains the cell cycle, repairs DNA or triggers the death of damaged cells; mutations that inactivate it allow uncontrolled division.
The pressure exerted by the contents of a plant cell against its cell wall, which builds up as water enters by osmosis; the wall pushes back with an equal pressure.
A form of diabetes in which the beta cells of the islets of Langerhans are destroyed by the body's own immune system, so little or no insulin is secreted.
A form of diabetes in which target cells become less sensitive to insulin (insulin resistance), so blood glucose is not lowered effectively even though insulin is secreted.
A small protein that is attached in chains to proteins that are to be destroyed, marking them for breakdown by proteasomes.
The filtration of blood plasma under high pressure in the glomerulus into Bowman's capsule, which removes water and small solutes but retains blood cells and plasma proteins.
Cell respiration in which the energy released is given out as heat instead of being used to make ATP, because protons flow back across the inner mitochondrial membrane through thermogenin instead of ATP synthase.
The feature of the genetic code that the same codons code for the same amino acids in almost all organisms.
The rising of cold, dense, nutrient-rich water from the deep ocean to the surface, often driven by winds pushing surface water away from a coast; it supports high primary production.
The main nitrogenous waste product of mammals, made in the liver from the excess amino groups of amino acids and excreted by the kidneys in urine.
The part of the menstrual cycle that takes place in the uterus: shedding of the endometrium at menstruation, then its repair and thickening.
The muscular organ of the female reproductive system in which an embryo implants and the fetus develops; also called the womb.
The narrowing of arterioles when the smooth muscle in their walls contracts, reducing blood flow through the capillaries they supply; in the skin it reduces heat loss.
The widening of arterioles when the smooth muscle in their walls relaxes, increasing blood flow through the capillaries they supply; in the skin it increases heat loss.
The potential energy of water per unit volume, relative to pure water at atmospheric pressure and 20 °C, which is given the value zero; symbol Ψ, usually measured in kPa.
A modified guanine nucleotide added to the 5′ end of eukaryotic pre-mRNA; it protects the mRNA from breakdown and is where ribosomes attach.