Biology

• Allele


  A version of a gene
• Blood group


  Classification of blood type as A, B, AB or O based on surface antigens on red blood cells and the presence of certain antibodies in the plasma. Blood group is controlled by three alleles, A, B and O.
• Chromosome


  A long, coiled molecule of DNA that carries genetic information in the form of genes.
• Codominance


  When both alleles for a gene in a heterozygous organism equally contribute to the phenotype.
• Colour blindness


  An X-linked recessive condition characterised by the inability to distinguish between colours. It is more common among males because they only inherit one X chromosome.
• Diploid cell


  A cell that contains a pair of each chromosome type e.g. human diploid cell has 23 pairs of chromosomes.
• Diploid nucleus


  A nucleus that contains two copies of each chromosome (i.e. a full set of chromosomes).
• Dominant


  Describes an allele that is always expressed. Represented by a capital letter.
• Gametes


  Sex cells (sperm and egg cells) with half the usual number of chromosomes.
• Gene


  A length of DNA on a chromosome that codes for the production of a specific protein.
• Gene expression


  All specialised cells contain the same set of genes, but only the genes required to code for certain proteins are switched on in any given cell.
• Genetic code


  The rules by which the sequence of bases in a gene codes for the sequence of amino acids in a specific protein.
• Genotype


  An organism's genetic composition. Describes all alleles.
• Haploid nucleus


  A nucleus that contains a single copy of each chromosome (i.e. half the number of chromosomes)
• Heterozygous


  When someone has two different alleles of a gene e.g. Ff.
• Homozygous


  When someone has two identical alleles of a gene e.g. FF or ff.
• Inheritance


  The transmission of genetic information from one generation to the next
• Meiosis


  A form of nuclear division that produces four genetically different daughter cells (gametes). It involves two divisions. Chromosome number is halved, resulting in haploid cells
• Mitosis


  A form of nuclear division that produces two genetically identical daughter cells from one parent cell. The copies of chromosomes are separated, maintaining the diploid chromosome number. Mitosis is importance in the growth, repair and replacement of cells, as well as asexual reproduction
• Monohybrid inheritance


  The inheritance of a single gene
• mRNA


  A polymer of nucleotides that carries genetic information from the nucleus to the ribosomes during protein synthesis
• Pedigree diagram


  A chart used to show the inheritance of a given characteristic in a family
• Phenotype


  An organism's observable characteristics due to interactions of the genotype and the environment
• Punnett square


  A grid used to predict the potential outcomes of a genetic cross
• Pure breeding


  A type of breeding in which all of the offspring carry the same phenotype as the parents. This occurs when two identical homozygous individuals are crossed
• Recessive


  Describes an allele that is only expressed in the absence of a dominant allele. Represented by a small letter
• Ribosomes


  Sub-cellular structures that are the site of protein synthesis
• Sex chromosomes


  A pair of chromosomes responsible for the determination of gender. XY in males, XX in females
• Sex-linked characteristic


  A characteristic that is coded for by an allele found on a sex chromosome
• Stem cells


  Cells that are unspecialised and capable of dividing by mitosis to produce a range of different cell types
• Test cross


  An individual with a dominant phenotype is crossed with a homozygous recessive individual. The ratio of offspring indicates the genotype of the dominant individual
• Variation


  The differences between individuals due to genes the onvironment
• Mitochondria are responsible for producing energy through aerobic respiration.
• The nucleus contains the genetic material (DNA) that controls all cellular activities.
• Inheritance


  The transmission of genetic information from parents to offspring
• Chromosome


  A thread-like structure of DNA that carries genetic information in the form of genes
• Gene


  A length of DNA that codes for a particular protein
• Allele


  One of a number of different versions of a gene
• Genotype


  The genetic makeup of an organism, consisting of all the alleles present
• Phenotype


  The observable features of an organism as a result of the expression of particular alleles of the gene