group 14-18

• Group 14 elements


  All have 4 valence electrons, tend to form 4 covalent bonds (share 4 electrons with other non-metals)
• Group 14 elements


  • Wide range of properties and uses, includes 1 non-metal (carbon), 2 metalloids (silicon, germanium) and 2 metals (tin, lead)
• Covalent bonding


  Occurs when an atom shares its valence electrons
• Group 14 elements have the largest number of covalent bonds an element can form, aside from a few complex exceptions</b>
•  Specialising in the field of genetics and molecular biology
• The halogens are typically coloured and toxic.

   

  The halogens all bond covalently to form diatomic molecules. This means two of the same atoms share electrons.

  •Fluorine is found as F2, an extremely toxic yellow gas.•Chlorine is found as Cl2, a highly toxic green gas.•Bromine is found as Br2, a toxic red-brown liquid.•Iodine is found as I2, a mildly toxic purple solid.

  The halogens are toxic because they can react with most of the chemical compounds in your body. This is also why the most reactive halogens are the most toxic.
• Mutation


  A change in the DNA sequence of an organism
• Mutations


  • Can result from errors in DNA replication during cell division
  • Can result from exposure to mutagens
  • Can result from viral infection
• Germline mutations


  Occur in eggs and sperm and can be passed on to offspring
• Somatic mutations


  Occur in body cells and are not passed on
• How mutations get passed

  1. Meiosis shuffles genetic material creating new combinations of genes, increasing chances of passing mutations to next generation

  2. Inherited mutations occur in germ cells (sperm and egg) and are passed on to offspring

  3. Mutated gene can be seen in offspring's phenotype through single dominant or two recessive mutated copies

  4. If mutation occurs in a germ cell, it can be included in the sperm or egg and passed on during fertilization
• Point mutation


  A genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence
• Types of point mutation

  • Nonsense mutation - stops protein from being made
  • Missense mutation - changes an amino acid
  • Silent mutation - has no phenotypic effect
• Chromosomal mutation


  Changes in the structure or number of entire chromosomes
• Types of chromosomal mutation

  • Deletion - loss of chromosome segment
  • Duplication - repetition of chromosome segment
  • Inversion - reversal of chromosome segment
  • Translocation - rearrangement of segments between non-homologous chromosomes
• Genomic mutation


  Change in the nucleotide sequence of a short region of a genome
• Types of genomic mutation

  • Aneuploidy - abnormal number of chromosomes, e.g. Trisomy 21 causing Down syndrome
  • Polyploidy - more than two sets of chromosomes (common in plants, rare in animals)
• Down syndrome


  Typical example of syndrome resulting from having one extra chromosome 21 (trisomy 21)
• How Down syndrome is caused

  1. When egg or sperm with extra chromosome 21 joins with regular egg or sperm, resulting zygote has 3 copies of chromosome 21

  2. Sometimes a chromosome doesn't split right during egg or sperm formation, and an extra one ends up in the cell
• Inheritance pattern of Down syndrome

  • Mostly not inherited from parents but caused by random error in cell division during formation of reproductive cells
  • In about 1-2% of cases, can be inherited if one parent carries a specific chromosomal rearrangement involving chromosome 21