module 6

• A genetic mutation is a change in the base sequence of DNA and they occur randomly during DNA replication which is within S phase of interphase
• Random mutations are more likely to occur if you're exposed to mutagenic agents
• Mutagenic agents

  • High energy radiation such as UV lights
  • Ionizing radiation such as gamma rays and x-rays
  • Chemicals which would be known as carcinogens such as mustard gas and a whole range that are in cigarette smoke
• Types of gene mutation

  • Deletion
  • Substitution
• Substitution mutation


  One of the nucleotides and therefore bases is swapped for a different base
• Deletion mutation


  One of the nucleotides and therefore bases in the sequence is removed
• A deletion mutation causes a frameshift where all the subsequent codons will code for a different amino acid
• Transcription factors


  Molecules that can bind to the DNA and either initiate or inhibit transcription
• Transcription factors are proteins that bind to DNA due to their unique 3D shape being complementary to a particular sequence of bases
• If a transcription factor binds, it enables RNA polymerase to bind and initiate transcription
• If a transcription factor doesn't bind, the gene is inactive because transcription cannot occur
• Transcription factors can inhibit RNA polymerase binding and therefore prevent transcription
• Operon


  A group of simultaneously controlled genes that are either all expressed or not, more common in prokaryotes
• The Lac operon in E. coli contains 3 genes involved in lactose digestion
• Lac repressor protein

  Inhibits transcription of the Lac operon when lactose is absent
• Cyclic AMP and its receptor protein CRP increase the rate of transcription of the Lac operon when lactose is present
• Epigenetics


  Heritable changes in gene function without changing the DNA base sequence
• Methylation


  Methyl groups bind to DNA, causing tighter coiling and preventing transcription factors from binding
• Acetylation


  Acetyl groups bind to histones, causing looser DNA packaging and allowing transcription factors to bind
• Decreased methylation or increased acetylation results in an open chromatin structure that allows transcription
• Increased methylation or decreased acetylation results in a closed chromatin structure that prevents transcription
• Pre-mRNA


  The newly synthesized mRNA before modifications
• Splicing


  The removal of introns (non-coding sequences) from pre-mRNA
• Alternative splicing can produce multiple mRNA molecules from one gene
• Post-translational modifications can add non-protein groups and fold the polypeptide into a unique 3D shape
• Homeobox genes


  Sequences of genes that regulate the expression of other genes involved in body formation
• Hox genes are a type of homeobox gene that control body segmentation and symmetry in animals
• Mitosis


  Cell division that increases cell number for growth and repair
• Apoptosis


  Programmed cell death that removes unwanted cells
• Tumor suppressor genes


  Genes that produce proteins to stop the cell cycle when more cells aren't needed
• Hox genes regulate mitosis and apoptosis in response to internal and external stimuli
• Genetic terms

  • Monohybrid
  • Codominance
  • Multiple alleles
  • Sex linkage
  • Autosomal linkage
  • Epistasis
• Monohybrid genetic diagram

  1. Determine parental genotypes

  2. Show gametes

  3. Show possible offspring genotypes and phenotypes
• If two carriers of a recessive cystic fibrosis allele reproduce, there is a 25% probability of having a child with cystic fibrosis
• The probability of having a girl with cystic fibrosis is half of the overall probability, since there is a 50% chance of having a girl or boy
• Determining probability of child with cystic fibrosis

  1. Work out parental genotypes

  2. Show gametes

  3. Determine possible genotypes and phenotypes

  4. Calculate probability of child with cystic fibrosis

  5. Calculate probability of girl with cystic fibrosis
• Codominance

  Both alleles are expressed, resulting in a blended phenotype
• Determining probability of red cows

  1. Identify parental genotypes

  2. Determine gametes

  3. Identify possible genotypes and phenotypes

  4. Calculate probability of red offspring
• Multiple alleles

  More than two alleles for a single gene
• Determining probability of blood group O offspring

  1. Identify parental genotypes

  2. Determine gametes

  3. Identify possible genotypes and phenotypes

  4. Calculate probability of blood group O offspring