genetics

• 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, with two sets of 23 chromosomes (one from each parent)
• Fertilisation


  The genetic information from each parent is mixed, producing variation in the offspring
• Asexual reproduction


  One parent with no gametes joining, using the process of mitosis to form two identical cells
• There is no mixing of genetic information in asexual reproduction, leading to clones
• 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
• 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 with 23 chromosomes join at fertilisation to produce a cell with 46 chromosomes, the normal number
• DNA


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


  The small parts that make up DNA
• Complementary base pairing


  A bases only connect to T bases, and C bases only connect to G bases
• Genetic code


  The order of the different bases in DNA
• Double helix


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


  A short section of DNA that codes for a specific protein
• Genome


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

  1. Gently mix water, salt and washing up liquid

  2. Pulverise kiwi fruit

  3. Add solution to kiwi

  4. Filter and add pineapple juice

  5. Add ethanol to precipitate DNA
• Bromelain


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

  The process of producing a protein from DNA
• Protein synthesis


  1. DNA contains genetic code for protein

  2. mRNA is created as a template

  3. mRNA moves to ribosomes

  4. Amino acids are brought to ribosomes by tRNA

  5. Amino acids connect to form polypeptide

  6. Polypeptide folds into final protein
• Genetic variants


  Small changes in the order of bases that make up DNA
• 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 is inserted
  • Base is deleted
  • Base is substituted
• Most mutations do not alter the protein or only do so slightly, but some can have a serious effect and change the shape of the protein
• Gregor Mendel


  Trained in mathematics and natural history, worked in monastery gardens and observed characteristics passed on to next generation in plants
• Mendel carried out breeding experiments on pea plants and published his work in 1866, concluding that offspring inherit 'hereditary units' from each parent, with one unit received from each parent, and units can be dominant or recessive
• 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