Genetics, Biodiversity, and Classification

• Adaptation: A feature of an organism that increases its chance of survival in its environment. An adaptation may be anatomical physiological or behavioural.
• Allele: A version of a gene.
• Anticodon: A sequence of three nucleotide bases at one end of a tRNA molecule that is specific to an mRNA codon.
• Arithmetic mean: The average of a set of numbers calculated by dividing the sum of the values by the number of values.
• Artificial classification: A type of classification that divides organisms into groups based on analogous characteristics such as leaf shape number of legs and type of wing.
• Binomial system: A universal system of naming organisms that consists of two parts: the generic name and the specific name e.g. Homo sapiens
• Biodiversity: The variety of genes species and habitats within a particular area.
• Chromatid: One strand of a replicated chromosome.
• Chromosome: A structure consisting of a long coiled molecule of DNA and its associated proteins by which genetic information is passed from generation to generation.
• Chromosome mutation: A change to the number or structure of chromosomes that can occur spontaneously.
• Classification: The organisation of organisms into groups. There are two types of classification: artificial and phylogenetic.
• Codon: A sequence of three bases on mRNA that codes for a specific amino acid.
• Conservation: The maintenance of ecosystems and biodiversity by humans in order to preserve the Earth’s resources.
• Courtship: The behaviour by which members of a species select reproductive partners. It enables organisms to recognise their own species identify a mate with a capacity to breed form a pair bond synchronise mating and become able to breed themselves.
• Crossing over: The process in meiosis 1 in which homologous chromosomes pair up their chromatids wrap around one another and their alleles are exchanged at equivalent portions of chromatids. This creates genetic variation.
• Degenerate: A feature of the genetic code; more than one triplet can code for a particular amino acid.
• Deletion: A form of gene mutation in which one or more nucleotide bases are removed from a DNA sequence. This may change all amino acids in a sequence rendering the protein non-functional.
• Directional selection: A type of selection that favours individuals that differ in one direction (fall to the left or the right) from the population mean. This changes the traits of the population.
• Ecosystem diversity: A measure of the range of different habitats in a particular area.
• Eukaryotic DNA: Linear molecules of DNA which together with histones form chromosomes. DNA in the mitochondria and chloroplasts of eukaryotic cells is circular and does not have associated proteins.
• Exon: A sequence of DNA that codes for an amino acid sequence.
• Fertilisation: The random fusion of haploid gametes during fertilisation to produce a diploid zygote. Genetic information is mixed 


  creating genetic variation.
• Gene: A length of DNA on a chromosome that codes for the production of one or more polypeptide chains and functional RNA.
• Gene mutation: A change to at least one nucleotide base in DNA or the arrangement of bases. Gene mutations can occur spontaneously during DNA replication.
• Generic name: Denotes the organism’s genus. The first letter is written in upper case 


  e.g. Homo.
• Genetic code: The rules by which triplets in a DNA base sequence code for the sequence of amino acids in a polypeptide chain. The genetic code is degenerate universal and non-overlapping.
• Genome: The entire set of genes in a cell.
• Histones: Proteins that 


  together with DNA form chromosomes in the nuclei of eukaryotic cells.
• Homologous chromosomes: A chromosome pair 


  one paternal and one maternal with the same gene loci.
• Independent segregation: The random separation of homologous chromosomes in meiosis 1 that produces genetic variation.
• Index of diversity (d): Describes the relationship between the number of different species and the abundance of individuals in each of these species within a community. It is calculated using the formula:
• Intron: A non-coding sequence of DNA.
• Meiosis: A type of cell division that produces four genetically different daughter cells (gametes) with a haploid number of chromosomes. It involves two divisions.
• Messenger RNA (mRNA): A type of RNA that carries genetic information from the nucleus to the ribosomes for protein synthesis. It is a single helix consisting of thousands of mononucleotides.
• Mitosis: A form of cell division that produces two genetically identical diploid daughter cells. Mutagenic agent: An agent that increases the rate of gene mutations above normal level.
• Natural selection: The process by which the frequency of ‘advantageous’ alleles gradually increases in a population’s gene pool over time.
• Non-coding sequence: A sequence of DNA that does not code for an amino acid sequence e.g. repeating base sequences and introns. Non-coding sequences make up significant portions of eukaryotic nuclear DNA.
• Non-overlapping: A feature of the genetic code; each base in a sequence is read once and is only part of one triplet.
• Phylogenetic classification: A type of classification that divides organisms into groups based on evolutionary relationships and homologous characteristics. It uses a hierarchy in which smaller groups are contained within larger groups with no group overlap.
• Phylogeny: The evolutionary relationships between individuals or groups of organisms. Prokaryotic DNA: Circular pieces of DNA that do not have associated proteins.