Bio Topic 3 (Paper 1)

• Sexual reproduction


  Involves the 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
  • Formed by meiosis, as they are non identical
• Normal cell


  Has 46 chromosomes, two sets of 23 chromosomes (one from each parent)
• Gametes


  Have 23 chromosomes, fuse in fertilisation
• Genetic information


  Mixed in sexual reproduction, producing variation in offspring
• Asexual reproduction

  Involves one parent with no gametes joining, happens using mitosis to form two identical cells
• Examples of organisms that reproduce asexually

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

  • Produces variation in offspring
  • Decreases chance of 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, used to produce haploid gametes
• Meiosis


  1. Cell makes copies of chromosomes

  2. Cell divides into two cells with half the chromosomes

  3. Cell divides again producing four genetically different cells with a quarter the chromosomes
• Gametes


  Cells with 23 chromosomes that join at fertilisation to produce a cell with 46 chromosomes
• DNA


  A chemical found in the nucleus that contains genetic material, made up of nucleotides with one sugar, one phosphate and one of four organic bases (A, C, G, T)
• DNA molecule


  Made up of two DNA strands twisted together, with complementary base pairing (A-T, C-G)
• Genetic code


  The order of the different bases in DNA
• DNA


  A polymer made up of two strands in a double helix structure
• Gene


  A short section of DNA that codes for many amino acids to make a specific protein
• Genome


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

  Mix water, salt and washing up liquid, heat, add kiwi, filter, add pineapple juice, add ethanol
• Bromelain


  Enzyme in pineapple juice that breaks down proteins attached to DNA
• Ethanol


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


  DNA contains genetic code, mRNA is made as a template, mRNA moves to ribosomes, amino acids are brought by tRNA and linked to form a polypeptide, polypeptide folds into final protein
• Genetic variants


  Small changes in the order of bases in DNA that can affect the structure of proteins
• Genotype


  The genes present in the DNA of an individual
• Phenotype


  The visible effects of the genes (e.g. the proteins they code for)
• Types of mutations


  • Base insertion
  • Base deletion
  • Base substitution
• Mutations


  Can change the type/sequence of amino acids, affecting the way the protein folds and functions
• Most mutations do not alter the protein or only do so slightly, but some can have a serious effect
• Gregor Mendel

  Trained in mathematics and natural history, worked in monastery gardens and observed characteristics passed on in plants, published work in 1866 on hereditary units
• Mendel's work was not recognised until after his death as genes and chromosomes were not yet discovered
• Gregor Mendel


  • Trained in mathematics and natural history in Vienna
  • Worked in the monastery gardens and observed the characteristics passed on to the next generation in plants
  • Carried out breeding experiments on pea plants
  • Used smooth peas, wrinkled peas, green peas and yellow peas and observed the offspring to see which characteristics they had inherited
  • Came to conclusions about hereditary units and how they are inherited
• Mendel was not recognised till after his death as genes and chromosomes were not yet discovered, so people could not understand
• Gamete


  An organism's reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23)
• Chromosome


  A structure found in the nucleus which is made up of a long strand of DNA
• Gene


  A short section of DNA that codes for a protein, and therefore contribute to a characteristic
• Alleles


  The different forms of the gene - humans have two alleles for each gene as they inherit one from each parent
• Dominant allele


  Only one (out of the two alleles) is needed for it to be expressed and the corresponding phenotype to be observed
• Recessive allele


  Two copies are needed for it to be expressed and for the corresponding the phenotype to be observed
• Homozygous

  When both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles)
• Heterozygous

  When one of the inherited alleles is dominant and the other is recessive