Module 6 Genetics, evolution and ecosystems

• Mutation


  A change in the DNA that could result in a non-functioning protein

  
• Gene


  A section of DNA that contains a code for making a polypeptide and functional RNA
• Gene mutation


  A change in the base sequence of DNA
• Mutagenic agents


  Agents that can interfere with DNA replication and increase mutation rate
• Mutagenic agents


  • High energy radiation (UV light)
  • Ionising radiation (gamma rays and X-rays)
  • Chemicals (carcinogens such as mustard gas and cigarette smoke)
• Types of gene mutation


  • Insertion - One extra base is added to the DNA sequence
  • Deletion - One base is deleted in the DNA sequence
  • Substitution - One base is swapped in the DNA sequence
• Frameshift mutation


  A change in all the codons after the point of mutation, each base shifts left or right one position

  
• Transcription factors


  Proteins that move from the cytoplasm into the nucleus to turn on/off specific genes
• Oestrogen


  A steroid hormone that can initiate transcription
• How oestrogen initiates transcription


  1. Oestrogen binds to a receptor site on the transcriptional factor

  2. It causes it to change shape slightly

  3. This change in shape makes it complementary and able to bind to the DNA to initiate transcription

  
• Operon


  A group of simultaneously controlled genes that are either all expressed or not
• Lac operon


  A sequence of three genes (LacZ, LacY, LacA) that collectively aid with lactose digestion in E.Coli
• LacI gene


  A regulatory gene found near the Lac operon that codes for a repressor protein that inhibits transcription when there is no lactose present
• Cyclic AMP (cAMP)


  Increases the rate of transcription of the Lac operon
• How cAMP increases Lac operon transcription


  1. CRP can only bind and increase the transcription rate once bound to cAMP

  2. In order for sufficient enzymes to be produced by LacZ, LacY and LacA, the cAMP receptor protein (CRP) must bind
• Epigenetics


  The heritable change in gene function without changing the DNA base sequence, caused by changes in the environment

  
• Epigenome


  A single layer of chemical tags on the DNA that impacts the shape of the DNA-histone complex and determines whether the DNA is tightly wound (won't be expressed) or unwound (will be expressed)
• Methylation of DNA


  Increased methylation of DNA inhibits transcription by preventing transcriptional factors from binding and attracting proteins that condense the DNA-histone complex
• Acetylation of histones


  Decreased acetylation of histone proteins inhibits transcription by making the histones more positive, so the DNA and histone proteins are strongly associated and it is harder for transcription factors to bind
• Pre-mRNA


  A newly synthesised strand of mRNA before modification, where introns are removed and protective caps are added

  
• Homeobox genes


  Sequences of genes which create proteins that regulate the expression of other genes involved in the formation of the body in the early stages of development as an embryo
• Hox genes


  A type of homeobox gene found in animals that are responsible for the correct body development and positioning of body parts
• Apoptosis


  Programmed cell death
• Tumour suppressor genes


  Genes that produce proteins to slow down cell division and cause cell death if DNA copying errors are detected
• Genotype


  The genetic constitution of an organism (the alleles an organism has for a gene)
• Phenotype


  The expression of the genes and their interaction with the environment
• Homozygous


  A pair of homologous chromosomes carrying the same alleles for a single gene
• Heterozygous


  A pair of homologous chromosomes carrying two different alleles for a single gene
• Recessive allele


  An allele only expressed if no dominant allele is present
• Dominant allele


  An allele that will always be expressed in the phenotype
• Codominant


  Both alleles are equally dominant and expressed in the phenotype
• Multiple alleles


  More than two alleles for a single gene, for example human blood groups
• Sex linkage


  A gene whose locus is on the X chromosome, for example colour blindness
• Autosomal linkage


  Genes that are located on the same chromosome (not the sex-chromosomes)
• Epistasis


  When one gene modifies or masks the expression of a different gene at a different locus
• Inheritance coding systems


  • Monohybrid inheritance
  • Dihybrid inheritance
• What should you include in a genetic cross?


  1. Parents' genotypes

  2. Gametes

  3. Offspring genotype

  4. Offspring phenotypes

  5. Probability of the offspring having the condition/feature

  
• Chi-squared statistic


  Can be used to see if the ratio you expected was significantly different to the ratio you observed
• Hardy-Weinberg principle


  A mathematical model used to predict the allele frequencies within a population, assuming no change in the allele frequency between generations
• Hardy-Weinberg components of the equation


  • p = frequency of the dominant allele
  • q = frequency of the recessive allele
  • p2 = frequency of the homozygous dominant genotype
  • 2pq = frequency of the heterozygous genotype
  • q2 = frequency of the homozygous recessive genotype