b6 inheritance

• What does DNA stand for?

  Deoxyribonucleic acid
• What is DNA?

  A set of chemical instructions that puts an organism together and makes it work
• What is a gene?

  A section of DNA that codes for amino acids to make specific proteins
• What are chromosomes?

  Long strands of DNA that are condensed and held in the nucleus
• Chromosomes usually come in pairs
• Structure of DNA

  • Polymer in the shape of a double helix
  • Made of repeating units called NUCLEOTIDES
  • Each nucleotide has a sugar molecule, phosphate molecule and a base
• What are the 4 bases in a DNA molecule?

  • A
  • T
  • C
  • G
• What bases pair up in complimentary base pairing?


  A and T, C and G
• What is the structure of double helix?

  Sugar and phosphate form a backbone and bases pair up in the middle - COMPLIMENTARY BASE PAIRING
• How many bases code for 1 amino acid?

  3
• 3 bases that code for an amino acid are called a codon
• A certain sequence of amino acids codes for a protein
• What are non-coding DNA?

  Parts of DNA that don't code for proteins, some switch genes on or off
• What is the genome of an organism?

  The entire genetic material of that organism
• What is the human genome project?

  A mission to study the whole human genome
• Benefits of sequencing the human genome

  • Genes that link to diseases can be searched, eg BRAC2 breast cancer gene
  • Enables understanding and treatment of inherited disorders
  • Human migratory patterns can be traced from the past
• Process of proteinsynthesis

  1. DNA unravels from its double helix form to be copied by mRNA
  2. Strand of mRNA is formed which is a copy of DNA code
  3. mRNA moves from the nucleus to the surface of the ribosome
  4. tRNA brings the correct amino acid based on the mRNA code
  5. One end of tRNA recognises mRNA codon, other end brings correct amino acid
  6. The sequence of amino acids results in a polypeptide protein
  7. Protein folds to form a unique shape to do its job correctly
• What is mRNA?

  Messenger RNA that is a copy of DNA from the nucleus
• What is tRNA?

  Transfer RNA which brings the correct amino acid to the mRNA codon
• Uses of proteins

  • Turn into enzymes - catalyst that speeds up reactions in the body
  • Turn into hormones - carries messages around body
  • Turn into structural proteins
• What is a mutation?


  A change in DNA bases
• Mutations

  • Occur randomly and continuously
  • Some are inherited
  • Most don't effect proteins
  • Some have serious effects and change the shape of the enzyme - no longer catalyses substance
  • Mutations in non-coding DNA alter gene expression
• Types of DNA mutation

  • Substitution
  • Deletion
  • Insertion
• Substitution mutation

  • A random base is changed to another base in a DNA sequence
  • Affects amino acid added so affects the protein made
  • NO KNOCK ON EFFECT - doesn't alter the number of bases
• Deletion mutation

  • Random base is deleted from DNA sequence
  • Changes in amino acids coded for
  • CAN HAVE A KNOCK ON EFFECT - changes the number of bases in sequence so alters amino acids further along too
• Insertion mutation

  • New base is inserted into DNA base sequence where it shouldn't be
  • Changes amino acid sequence so protein is changed
  • CAN HAVE KNOCK ON EFFECT - changes number of bases in a DNA sequence so changes amino acids further along
• Mitosis

  1. Cell grows, increases number of subcellular structures
  2. DNA duplicates
  3. Copied DNA forms X-shaped chromosomes
  4. Chromosomes line up at centre of the cell and cell fibres pull apart
  5. Arms of chromosomes go to opposite ends of cell
  6. Membranes form and act as new nucleus
  7. Cytoplasm and cell membranes divide
  8. Forms 2 identical daughter cells
• Meiosis

  1. DNA duplicates and number of subcellular structures increases
  2. Chromosomes line up at the centre of the cell and are pulls apart by cell fibres
  3. Nucleus divides, cell membrane splits
  4. Second division with the same process
  5. Produces 4 daughter cells - HAPLOID
  6. Produces gametes - sex cells (sperm,egg)
• Where does meiosis occur?

  Testes and ovaries
• Each gamete is genetically DIFFERENT to the original cell - chromosomes are shuffled during meiosis
• Similarities of mitosis and meiosis

  • Both begin with diploid cells
  • Both undergo DNA replication before division
  • Both have division of cytoplasm
• Differences between mitosis and meiosis

  • Mitosis ends with diploid cells (46 chromosomes)
  • Meiosis ends with haploid cells (23 chromosomes)
  • Mitosis makes normal cells
  • Meiosis makes gametes
  • Mitosis has 1 round of division
  • Meiosis has 2 round of division
• Asexual reproduction

  • Cells divide into 2 IDENTICAL CELLS for growth and to replace tissues in the body
  • No variation - no mixing of genetic information
  • Makes clones
  • Only involves 1 parent - cells divide by mitosis
  • Occurs in small animals, plants, fungi, bacteria
• Sexual reproduction

  • Involves 2 parents - male and female sex cells (gametes)
  • Cells fuse together and make a zygote
  • Gametes formed by meiosis
  • Variation - offspring get genetic information from both parents so they aren't identical to them
  • Risky - relies on 2 sex cells meeting and using
• Why are gametes formed by meiosis?

  They only have half of the chromosomes (23) a normal cell would

  So gametes join to have the correct number (46)
• What are the gametes in plants?

  Egg and pollen
• What are the gametes in animals?

  Egg and sperm cells
• What are gametes?

  Sex cells
• Sexual reproduction shows more variation than asexual
• Variation is important for long term survival of a species