Terminology

• Alleles


  Different forms of a gene which occur at the same locus on homologous chromosomes
• Genotype


  Genetic composition of an organism
• Phenotype


  The physical appearance of an organism based on the genotype, e.g. tall, short
• Dominant allele


  An allele that is expressed (shown) in the phenotype when found in the heterozygous (T) and homozygous (TT) condition
• Recessive allele


  An allele that is masked (not shown) in the phenotype when found in the heterozygous (Tt) condition; only expressed in the homozygous (tt) condition
• Heterozygous


  Two different alleles for a particular characteristic, e.g. Tt
• Homozygous


  Two identical alleles for a particular characteristic, e.g. TT or tt
• Monohybrid cross


  One characteristic or trait is shown in the genetic cross
• Dihybrid cross


  Two different characteristics shown in genetic cross
• Complete dominance


  The dominant allele masks the expression of the recessive allele in the heterozygous condition
• Incomplete dominance


  The offspring has an intermediate phenotype between the two parental phenotypes
• Genetic cross


  Cross between two phenotypically different parents produces offspring different from the parents
• Red-flowered plant x white-flowered plant with incomplete dominance


  • Offspring will have pink flowers - intermediate colour
• Co-dominance


  Both alleles are expressed equally in the phenotype
• Blood group alleles


  • A
  • B
  • i
• An individual can only have two alleles at the same locus
• Sex-linked characteristics


  • Traits carried in the sex chromosomes, e.g. haemophilia and colour blindness
• Haemophilia and colour blindness are caused by recessive alleles
• Homologous pair of chromosomes


  A set of one maternal and one paternal chromosome that pair up with each other inside a cell during meiosis, of the same size and shape, and carry the same or similar alleles
• Karyotype


  The number, shape and arrangement of the chromosomes in the nucleus of a somatic cell
• Genetic modification


  Manipulation of the genetic material of an organism to get desired changes
• Insertion of the human Insulin gene into the plasmid of bacteria


  • Bacteria produce human Insulin
• Cloning


  Process by which genetically identical organisms are formed using biotechnology
• Dolly the sheep was cloned using a diploid cell from one parent, therefore it had the identical genetic material of that parent
• Human genome


  Mapping of the exact position of all the genes in all the chromosomes of a human
• Example: haemophilia is the last gene on the X chromosome; gene number 3 on chromosome 4 is responsible for a particular characteristic
• Hereditary 


  passing of hereditary characteristics from parent to offspring.
• Filial generation (F1)


  Offspring of parent organisms
• Locus


  The exact position of a gene on a chromosome
• Genetic engineering 


  Techniques used to change the genetic material of a cell or living organism - a form of biotechnology
• Gene


  A segment of DNA in a chromosome that contains the code for a particular characteristic