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• Mutation


  Change in the sequence of nucleotides in DNA molecules
• Types of mutations


  • Insertion/deletion
  • Point mutation/substitution
  • Nonsense
  • Missense
  • Silent
• Insertion/deletion mutation


  • One or more nucleotide pairs are inserted or deleted from the sequence
  • Alters the sequence of nucleotides after the insertion/deletion point known as a frameshift
• Point mutation/substitution


  • One base pair is replaced by another
• Nonsense mutation


  • Translation is stopped early thus giving rise to a truncated polypeptide due to premature introduction of a stop codon
• Missense mutation


  • Codon change which results in the production of a different amino acid, thus resulting in altered tertiary structure of the protein
• Silent mutation


  • Codon change which does not affect the amino acid sequence produced
• Mutations can either have neutral effects, be beneficial, or be harmful
• Whether a mutation proves to be beneficial or detrimental to an organism will depend on the environment of the organism
• Controlling gene expression


  1. Transcriptional

  2. Post-transcriptional

  3. Post-translational
• Lac operon


  A length of DNA composed of structural genes and control sites which controls the expression of beta-galactosidase responsible for hydrolysis of lactose in E.coli
• Lac operon


  1. Promoter region

  2. Operator region

  3. Structural genes
• Glucose concentration is high and lactose concentration is low


  Transcription of structural genes is inhibited
• Glucose concentration is low and lactose concentration is high


  Lactose binds to the repressor, RNA polymerase can bind to the promotor region, transcription of structural genes takes place
• Transcription factors


  Have the ability to switch genes on and off through interaction with the promoter sequence of DNA to either initiate or inhibit transcription
• Post-transcriptional control


  Editing of the primary mRNA transcript, removing non-coding regions (introns) to create a mature transcript consisting only of protein-producing regions (exons)
• Post-translational control


  Proteins such as adrenaline can be activated with the help of cyclic AMP
• Homeobox genes


  Involved in controlling the development of body plan of organisms, code for transcription factors that bind to DNA to regulate transcription by switching genes on and off when they are required at particular stages of development
• Apoptosis


  A form of programmed cell death which can act as a mechanism to control the development of body plans, an ordered, controlled series of biochemical events leading to cell death
• Apoptosis is the opposite of necrosis, which is cell death resulting from damage and release of hydrolytic enzymes
• Apoptosis is a means of controlling the number of cells and ensuring that it remains constant to prevent cancer
• Discontinuous variation


  Variation which can be assigned to a particular category, e.g. shoe size or blood type
• Continuous variation


  Variation where the differences between phenotypes are quantitative, e.g. height or weight
• Variation can be influenced by both environmental factors and genetic factors
• Meiosis


  A form of cell division that gives rise to genetic variation, produces haploid gametes
• Meiosis


  1. Crossing over of chromatids

  2. Independent assortment of chromosomes

  
• Allele


  Alternative form of a gene
• Locus


  The specific position of a gene on a chromosome, the two alleles of a gene are found at the same loci on the chromosome pairs
• Phenotype


  Observable characteristics of an organism which are as a result of genotype and environment
• Genotype


  The alleles present within cells of an organism, for a particular trait or characteristic
• Dominant


  Only a single allele is required for the characteristic to be expressed, that allele is always expressed in the phenotype
• Recessive


  The characteristic is only expressed if there is no dominant allele present
• Homozygous


  Two identical alleles
• Heterozygous


  Two different alleles
• Codominance


  Both alleles contribute to the phenotype
• Linkage


  Genes for different characteristics are located at different loci on the same chromosome and so are inherited together
• Monogenic inheritance


  A phenotype or trait is controlled by a single gene
• Dihybrid cross


  Inheritance of two genes
• Sex linkage


  Expression of an allele dependent on the gender of the individual as the gene is located on a sex chromosome
• Autosomal linkage


  Genes which are located on the same chromosome (which is not a sex chromosome) and tend to be expressed together in the offspring