Phenotype

• Phenotype


  The characteristics of an organism, which result from the interaction of the genes of the organism with the environment in which it lives
• Types of variation in phenotype


  • Continuous
  • Discontinuous
• Continuous variation


  Variation within a range, includes mass and height
• Discontinuous variation


  Can only take particular values, such as gender or shoe size
• Variation in genotype


  Has an effect on variation in phenotype
• Monogenic characteristics


  Influenced by one gene only, show discontinuous variation
• Polygenic inheritance


  Several genes at different loci are involved in determining a characteristic, often gives rise to continuous variation
• Characteristics influenced by both genotype and environment


  • Height
  • Lung cancer risk
• Epigenetic modifications


  Modifications to DNA which do not change the base sequence. They modify the activation of certain genes
• DNA methylation


  Process by which methyl groups are added to DNA. It modifies the function of DNA, typically acting to suppress gene transcription. The change is permanent and prevents the cell from converting back into a stem cell or a different cell type
• Histone modification


  Acetylation (addition of an acetyl (COCH3) group) activates chromatin and allows transcription. Methylation (addition of a methyl group) can cause activation or inactivation of chromatin
• Lac Operon


  1. Gene in bacteria is suppressed by repressor molecules in the absence of lactose, preventing energy expenditure in transcribing the gene for lactose digesting proteins

  2. When lactose is present, it prevents the repressor molecules from binding to the operator region of the DNA, allowing the gene to be transcribed, thus its proteins produced