Genetics

• Benefits of understanding the human genome


  • Helps search for genes linked to diseases like cancer and Alzheimer's
  • Helps understand and treat inherited disorders like cystic fibrosis
  • Helps trace human migration patterns from the past
• Sexual reproduction


  Genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent
• Sexual reproduction


  1. Father and mother produce gametes (reproductive cells)

  2. Gametes only contain half the number of chromosomes of normal cells (haploid)

  3. Gamete fusion (male and female) produces a fertilised egg (zygote) with the full set of chromosomes (diploid)

  4. Zygote undergoes cell division (mitosis) and develops into an embryo

  5. Embryo inherits characteristics from both parents
• Meiosis


  A type of cell division that produces genetically different cells, unlike mitosis
• Meiosis


  1. Cell duplicates its DNA before division

  2. Chromosomes line up in pairs in the centre of the cell (one from mother, one from father)

  3. Pairs are pulled apart, each new cell gets one copy of each chromosome (mixture of mother's and father's)

  4. Second division separates the chromosome arms (chromatids)

  5. Results in 4 haploid daughter cells (gametes), each genetically different
• Organisms that can reproduce

  • Sexually
  • Asexually
  • Both
• Asexual reproduction


  • Cells divide by mitosis, resulting in genetically identical daughter cells
• Sexual reproduction


  • Involves meiosis and production of genetically different haploid gametes, which fuse to form a diploid cell at fertilisation
• Advantages and disadvantages of asexual and sexual reproduction

  • Asexual: Rapid, efficient
  • Sexual: Introduces genetic variation
• Gametes

  Reproductive cells that contain half the normal number of chromosomes
• Gametes are formed from the stigma
• Each chromosome has an identical shape
• Half of the chromosomes in the stand cell will be inherited from the organism's father (blue) and half from its mother (red)
• Advantages of asexual reproduction

  • Produces lots of offspring very quickly
  • Only one parent is needed
  • Organisms can reproduce whenever conditions are favourable, without having to wait for a mate
• Disadvantages of asexual reproduction

  • No genetic variation between offspring in the population
  • If the environment changes and conditions become unfavourable, the whole population may be affected
• Advantages of sexual reproduction

  • Creates genetic variation within the population
  • If the environmental conditions change, it's more likely that at least some individuals in the population will have the characteristics to survive the change
  • Can lead to natural selection and evolution as species become better adapted to their new environment
• Disadvantages of sexual reproduction

  • Takes more time and energy than asexual reproduction, so organisms produce fewer offspring in their lifetime
  • Two parents are needed, which can be a problem if individuals are isolated
• DNA


  Instructions for your characteristics
• DNA strands


  • Polymers made up of lots of repeating units called nucleotides
  • Each nucleotide consists of a sugar, a phosphate group and one 'base'
  • The sugar and phosphate groups form a 'backbone' to the DNA strands
  • One of four different bases joins to each sugar: A (adenine), T (thymine), C (cytosine) and G (guanine)
  • A DNA molecule has two strands coiled together in the shape of a double helix
  • Each base links to a base on the opposite strand in the helix
  • A always pairs up with T, and C always pairs up with G (complementary base pairing)
• Chromosomes


  Long, coiled up molecules of DNA found in the nucleus of eukaryotic cells
• Genes


  Sections of DNA on a chromosome that code for a particular protein
• Genome


  All of an organism's DNA
• How to Extract DNA

  1. Mash strawberries

  2. Put in beaker with detergent and salt solution

  3. Mix well

  4. Filter mixture

  5. Add ice-cold alcohol

  6. DNA precipitates as stringy white solid
• Detergent


  Breaks down cell membranes to release DNA
• Salt


  Makes the DNA stick together
• Cold alcohol


  DNA is not soluble in, causing it to precipitate out
• You can fish out the precipitated DNA with a glass rod
• DNA


  Part of a DNA double helix
• DNA


  • Determines how all the cells in the body function
• Protein synthesis


  DNA controls the production of proteins in a cell
• Proteins


  Made up of chains of molecules called amino acids
• Protein


  Each different protein has its own particular number and order of amino acids
• Protein shape


  The amino acid chains fold up to give each protein a different, specific shape
• Enzyme


  Has active sites with a specific shape, and so only catalyse a specific reaction
• Gene


  A section of DNA that codes for a particular protein
• Genetic code


  The order of the bases in a gene decides the order of amino acids in a protein
• Base triplet


  Each amino acid is coded for by a sequence of three bases in the gene
• Protein synthesis


  The amino acids are joined together to make proteins, following the order of the bases in the gene
• Many regions of DNA are non-coding-that means that they don't code for any amino acids
• Some non-coding regions are still involved in protein synthesis