AQA A-Level Biology I Unit 4 Genetic Information I Primrose Kitten

GENE

A section of DNA that contains the coded information [i.e. a sequence of organic bases] to make a polypeptide or functional RNA.

LOCUS

The position and location of a particular gene [section of DNA].

DEGENERATE CODE

The genetic code where amino acids are each coded for by more than one triplet of bases except for methionine and tryptophan.

NON-OVERLAPPING

Reference to the genetic code. Each base in a sequence is read only once.

UNIVERSAL

With a few minor exceptions, each triplet of bases codes for the same amino acid in all organisms.

EXON

A coding sequence of bases.

INTRON

Non coding sequences of bases made up of multiple repeats of base sequences.

CHROMOSOME

A thread like structure made from a long single helix of DNA combined with proteins called histones. The DNA - histone complex is coiled and the coils fold to form loops. The loops coil and pack together to form a chromosome. Chromosomes carry genetic information.

CHROMATID

One of two strands held together by a centromere in a chromosome, once DNA has replicated during the S phase of interphase. They become visible at prophase and metaphaseof mitosis or meiosis.

HISTONES

A class of basic proteins, with an unusually large proportion of the basic amino acids, arginine and lysine. Histones are associated with DNA in the chromosomes of eukaryotic cells.

HOMOLOGOUS PAIR

Chromosomes which contain identical sets of gene loci. One chromosome in the pair has originated from the paternal sperm and the other from the maternal ovum/egg. Homologous chromosomes carry the same genes but not necessarily the same alleles of the genes.

DIPLOID

A cell that contains two copies of each chromosome.

HAPLOID

A single set of unpaired chromosomes in each nucleus. A cell that only contains one copy of each chromosome.

ALLELE

A variant of a gene that is found at the same locus on the chromosome and codes for the same polypeptide as another allele for the same gene. The polypeptides coded by different alleles may differ by one or more amino acids.

DEOXYRIBONUCLEIC ACID [DNA]

A nucleic acid found in the nuclei of eukaryotic cells and in mitochondria and chloroplasts. Made from two polynucleotide chains held together by hydrogen bonds between complementary base pairs, so forming a double helix. Each nucleotide consists of a phosphate group, a pentose sugar, deoxyribose and one of four organic bases [adenine, guanine, thymine and cytosine]. DNA provides the long term storage of genetic information; the sequence of bases code for the assembly of amino acids to make polypeptides.

RIBONUCLEIC ACID [RNA]

A nucleic acid found in the nucleolus of eukaryotic cells and in the cytoplasm as ribosomes or attached to rough endosplasmic reticulum. Made from a single polynucleotide chain. Each nucleotide consists of a phosphate group, a pentose sugar ribose and one of four organic bases [adenine, guanine, uracil and cytosine]. RNA has a role in transcription and translation of DNA during protein synthesis.

CODON

A triplet of bases found on mRNA, that codes for a single amino acid.

ANTICODON

A triplet of complementary bases to the mRNA codon, carried on tRNA.

GENOME

The complete set of genes in a cell, including those in mitochondria and/or chloroplasts

PROTEOME

The full range of proteinsproduced by a specific cell type under a certain set of conditions.

TRANSCRIPTION

The process of copying exactly the sequence of bases which code for a polypeptide in a section of DNA , into mRNA.

TRANSLATION

The process by which the base sequence in mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked together to form a polypeptide.

PRE-mRNA

Produced during transcription in eukaryotic cells. Pre mRNA contains sections called exons which code for proteins and non coding sections called introns.

SPLICING

The process which removes the intron non coding base sequences from pre-mRNA and the functional coding exons are joined together in the nucleus.

RNA POLYMERASE

An enzyme which joins RNA nucleotides together to form pre-mRNA, during transcription

MESSENGER RNA [mRNA]

A single polynucleotide chain, smaller than DNA but larger than tRNA. Helical in shape. Manufactured in the nucleus during transcription but found throughout the cell.

TRANSFER RNA [tRNA]

A single small polynucleotide chain folded into a clover shaped molecule, with one end extending beyond the other to enable attachment to an amino acid. The opposite end ontains an anticodon loop with three bases forming an anticodon.

MUTATION

A change in the genetic material in a cell. It may be a chromosome change or a change in the DNA nucleotide sequence of a gene.

GENE MUTATION

Any change to one or more nucleotide bases, or a change in the sequence of bases in DNA. Gene mutations can occur during substitution of one base with another; insertion or deletion of one or more base pairs, causing a frame shift.

CHROMOSOME MUTATION

Changes in the structure or number of chromosomes in a cell.

SILENT MUTATION

A substituiton of a base results in a different triplet to the original one but it codes for the same amino acid. This is because the genetic code is degenerate.

NON DISJUNCTION

A process which occurs during anaphase 1 of meiosis. Individual homologous pairs of chromosomes fail to separate and usually results in a gamete having either one more or one less chromosome.

HYBRIDISATION

The combination of genes of different varieties or species of organisms, to produce a hybrid.

POLYPLOIDY

Having three or more complete sets of chromosomes. Polyploidy is common in plants but rare in animals. This is mainly because polyploid individuals are sterile when crossed with diploids. A polyploid suddenly arising in a diploid population can only reproduce asexually or by self-fertilisation.

GAMETE

Another name for a sex cell. A reproductive cell which carries only one copy of each chromosome. Female gametes are called the ova or eggs; the male gametes are called sperm.

CHIASMA

[plueral chiasmata]. The point of contact during crossover of non-sister chromatids of homologous chromosomes during prophase 1 of meiosis. The process can result in the exchange of alleles and is much more frequent during meiosis than mitosis.

INDEPENDENT SEGREGATION

Pairs of homologous chromosomes line up at random on the spindle apparatus during metaphase 1 of meiosis. The combination of chromosomes of maternal and paternal origin that go into the two daughter cells is a matter of chance.

INDEPENDENT ASSORTMENT

The alleles of two or more different genes get shuffled into gametes independently of one another i.e the allele a gamete inherits from one gene does not influence the allele received from a second gene [unless they are found close to each other on the same chromosome ]

GENETIC DIVERSITY

The total number of different alleles in a group of individuals of the same species that live in the same place and can interbreed.

ALLELE FREQUENCY

The number of times an allele occurs within the gene pool.

GENE POOL

All the alleles of all the genes of all the individuals of the same species that occupy a particular space, at a particular time.

DIRECTIONAL SELECTION

A type of selection that favours one extreme of the range of phenotypes so the population changes over time

STABILISING SELECTION

Type of selection that operates against the extremes of the range of phenotypes. This preserves the characteristics of a population so the population remains the same over time.

POLYGENES

Genes which individually have a very small effect on phenotype differences but collectively influence phenotypic characteristics that vary about a mean. Characteristics controlled by polygenes are more influenced by environmental effects than those detemined by a single gene.

SPECIES

A group of organisms of common ancestry that interbreed to produce fertile offspring.

BINOMIAL SYSTEM

A system of naming species in which each species has two names: a generic name and a specific epithet e.g. Homo sapiens

TAXON

A group of organisms at any rank in the hierarchical classification scheme devised by Linnaeus e.g. any named species, genus, family order, class, phylum or kingdom.

PHYLOGENY

The evolutionary relationships between organisms. The evolutionary history of a particular taxon.

ARTIFICIAL CLASSIFICATION

Divides organisms according to differences that are useful at the time i.e. analogous characteristics such as colour, size, number of legs. For example wings of butterflies and birds are both used for flight but they have different evolutionary origins.

TAXONOMY

The study and practice of naming and classifying species and groups of species within the hierarchical classifcation scheme.

DOMAIN

The highest taxonomic rank above the rank of kingdom introduced by Carl Woese in 1990, giving greater weight to molecular biology. There are three domains: Bacteria; Archaea and Eukarya.

ARCHAEA

A group of single celled prokaryotes that were originally classified as bacteria. They are different from bacteria as a) histone proteins are associated with DNA b) membranes contain fatty acid chains attached to glycerol by ether linkages c) they have no murein in their cell walls d) introns are present in some genes e) contain several types of RNA polymerase.

EUKARYA

A domain divided into four kingdoms: Protoctista; Fungi; Plantae and Animalia. Their cells possess membrane bound organelles; they have larger 80s ribosomes; membranes containing fatty acid chains attached to glycerol by ester linkages.

BIODIVERSITY

The number of different ecosystems and habitats in an area, the number of species within those ecosystems and the genetic variation within each species.

SPECIES DIVERSITY

The number of different species and the number of individuals of each species within one community.

ECOSYSTEM DIVERSITY

The range of different habitats from a small local habitat to the whole of the Earth.

SPECIES RICHNESS

The number of different species found in a particular area at a given time.

SPECIES EVENNESS

The number of different species and their abundance found in a particular area at a given time.

BIOMASS

The mass of biological material measured as wet mass or, more often dry mass to overcome fluctuations in water content.

COMMUNITY

An ecological term for a group of populations of two or more species which occupy the same geographical area at the same time.

ECOSYSTEM

An ecological term for the interaction of the all the living [biotic] and non-living [abiotic] factors in a specific environment.

INTERCROPPING

A multiple cropping practice where two or more different species of plants are grown in close proximity e.g. one crop is grown between the rows of another crop, often to increase yields; pest control; suppress weeds.

INTERSPECIFIC VARIATION

Differences that occur between members of different species.

INTRASPECIFIC VARIATION

Differenced that occur between members of the same species.

MEAN

Arithmetic mean. The sum of the sampled values divided by the number of items.

MEDIAN

This is the central or middle value of a set of values. This requires arranging the values in ascending order,

MODE

This is the single value of a sample that occurs most often.

STANDARD DEVIATION

Used in statistics to measure the spread of the sample values from the mean. It is a better measure of spread than the range because standard deviation is less affected by extreme values.

POOTER

Equipment used to suck up small invertebrate animals into a glass or plastic tube, when investigating local biodiversity.

SWEEP NET

Large net which is often used to catch flying insects or insects which live in long grass.

PITFALL TRAPS

Cans or jars buried in the ground, filled with paper or cardboard to provide shelter and covered with a lid or stone to keep out the rain. These are used to collect ground dwilling insects, which are often nocturnal.

TULLGREN FUNNEL

A piece of equipment which is used to extract small invertebrates especially arthropods from soil or leaf litter.

BEATING TRAY

A large white sheet is placed on the ground or supported by struts and held below a tree. The tree is shaken to dislodge the animals. Very small animals can be collected from the beating tray with a pooter.

HABITAT

A place where a species lives, expressed in one or few words e.g. pond, lake, river, coral reef, grassland; sand dune; deciduous woodland; heathland.

NICHE

The role of a species in an ecosystem. A niche includes a description of all a species' interactions with the different factors in its environment [i.e. its' address and its profession'.]

TRIPLET CODE

A sequence of three nitrogenous bases read along the DNA strand that code for amino acids.

TRANSCRIPTION

The process of copying the triplet code from a DNA template into a single strand of mRNA.