Genetics

• Contents


  • 3.1B and 3.2B - Advantages and Disadvantages of Sexual and Asexual Reproduction
  • 3.3 - Role of Meiosis
  • 3.4 - The Structure of DNA
  • 3.5 and 3.6 - The Genome and Extracting DNA
  • 3.7B and 3.8B - The Stages of Protein Synthesis
  • 3.9B and 3.10B - Genetic Variants and their Effects
  • 3.11B - Mendelian Genetics
  • 3.12 - Alleles
  • 3.13 - Basic Genetics Terminology
  • 3.14 - Monohybrid Inheritance and Genetic Diagrams
  • 3.15 - Sex of Offspring
  • 3.16 - Outcomes and Pedigree Analysis
  • 3.17B - ABO Blood Group Inheritance
  • 3.18B - Sex-linked Inheritance
  • 3.19 - Multiple-Gene Inheritance and Causes of Variation
  • 3.21, 3.22 and 3.23 - Human Genome Project, Genetic Variation and Mutation affecting Phenotype
• Sexual reproduction


  Joining of male and female gametes, each containing genetic information from the mother or father
• Gametes


  • Sperm and egg cells in animals
  • Pollen and egg cells in flowering plants
• Gametes are formed by meiosis, as they are non identical
• A normal cell has 46 chromosomes, there are two sets of chromosomes (i.e. 23 pairs), one from the father and one from the mother
• Each gamete has 23 chromosomes and they fuse in fertilisation
• The genetic information from each parent is mixed, producing variation in the offspring
• Asexual reproduction


  Involves one parent with no gametes joining, happens using the process of mitosis, where two identical cells are formed from one cell
• There is no mixing of genetic information in asexual reproduction
• Asexual reproduction leads to clones, which are genetically identical to each other and the parent
• Organisms that reproduce asexually


  • Bacteria
  • Some plants
  • Some animals
• Advantages of sexual reproduction


  • Produces variation in offspring
  • Decreases the chance of the whole species becoming extinct
  • Allows selective breeding
• Advantages of asexual reproduction


  • Only one parent is needed
  • Uses less energy and is faster as organisms do not need to find a mate
• Meiosis


  The formation of four non-identical cells from one cell
• Meiosis


  1. The cell makes copies of its chromosomes

  2. The cell divides into two cells, each with half the amount of chromosomes

  3. The cell divides again producing four cells, each with a quarter the amount of chromosomes

  4. These cells are called gametes and they are all genetically different from each other
• Gametes with 23 chromosomes join at fertilisation to produce a cell with 46 chromosomes, the normal number
• This cell divides by mitosis to produce many copies, and an embryo forms
• The cells begin to take on different roles after this stage (differentiation)
• DNA


  A chemical that contains genetic material, found in the nucleus
• Nucleotides


  The small parts that DNA is made up of
• Each nucleotide is made up of one sugar molecule, one phosphate molecule and one of the four types of organic bases (A, C, G, T)
• DNA molecule


  Made up of two DNA strands which are twisted together, with each base connected to another base in the other strand (complementary base pairing)
• Genetic code


  The order of the different bases (A, G, T, T, C, A, A etc.)
• Double helix


  The structure of DNA, two strands wound around each other
• Gene


  A short section of DNA that codes for many amino acids, which are joined together to make a specific protein
• Genome


  All the genetic information (DNA) of a single organism
• Extracting DNA from fruit


  1. Gently mix together 50ml cold water, half a teaspoon of salt and 10ml washing up liquid, heat at 50C for 5-10 minutes

  2. Peel and chop kiwi, pulverise

  3. Add the solution to the kiwi

  4. Filter the solution using a sieve and kitchen paper

  5. Add 10ml of pineapple juice to the filtrate and allow to rest for a few minutes

  6. Add 2 teaspoons of cold ethanol to the solution and wait 10 minutes
• A white mass should precipitate at the top of the tube after 10 minutes, this is the DNA from the kiwi
• Bromelain


  An enzyme in pineapple juice that breaks down proteins attached to the DNA
• Ethanol


  Causes the DNA to precipitate out of the solution, making it visible
• Protein synthesis


  The process of producing a protein from DNA
• Protein synthesis


  1. DNA contains the genetic code for making a protein, but it cannot move out of the nucleus

  2. The mRNA nucleotides are joined together, creating an mRNA strand template

  3. RNA polymerase binds to non-coding DNA located in front of a gene on the DNA strand

  4. The two strands of DNA pull apart, and RNA polymerase allows mRNA nucleotides to match to their complementary base on the strand

  5. The mRNA moves out of the nucleus to the cytoplasm and onto ribosomes

  6. At the ribosomes, the bases on the mRNA are read in threes (triplets) to code for an amino acid

  7. The corresponding amino acids are brought to the ribosomes by tRNA carrier molecules

  8. These amino acids connect together to form a polypeptide

  9. When the chain is complete the protein folds to form a unique 3D structure
• Genetic variants


  Small changes in the order of bases that make up a strand of DNA
• Genotype


  The genes present in the DNA of an individual

  
• Phenotype


  The visible effects of those genes (e.g the proteins that they code for)
• A genetic variant in coding DNA will alter the sequence of amino acids, changing the final structure of the protein produced
• A genetic variant in non-coding DNA can affect the amount of RNA polymerase that can bind, changing the structure of the final protein
• Types of mutations


  • A base is inserted into the code
  • A base is deleted from the code
  • A base is substituted
• Most mutations do not alter the protein or only do so slightly
• Some mutations can have a serious effect and change the shape of the protein, so the substrate will not fit into the active site or a structural protein may lose its shape