DNA

• DNA is the genetic material found in the chromosomes in the nuclei of cells
• Chromosome


  A string of genes
• Gene


  A short piece of DNA that codes for a specific protein
• DNA


  • A long, coiled molecule formed from two strands
  • The two strands are twisted in a double helix
  • The strands are joined by pairs of bases
  • There are four different bases in DNA: A, C, T, G
  • Bases form complementary pairs: A always pairs with T, C always pairs with G
• Nucleotide


  The monomers that DNA is made of
• DNA can be extracted from fruit by grinding the fruit with sand, using a pestle and mortar, to separate the cells, adding a detergent to break open the membranes, and adding ice-cold alcohol so that the DNA precipitates out
• You do not need to know the names of the bases, you just need to know their letters are A, C, T and G
• The sequence of bases on one strand of DNA is CGAT
• The sequence of bases on the complementary strand is GCTA
• DNA structure


  1. Phosphate

  2. Base

  3. Deoxyribose sugar
• When gametes fuse at fertilisation, they form a diploid zygote. Each zygote inherits different alleles (genetic variants) of their genes from their parents
• Allele


  Different forms of the same gene
• Homozygous


  Having two copies of the same allele
• Heterozygous


  Having two different alleles of the same gene
• The gene for coat colour in rabbits has different alleles. The allele for brown colour (B) is dominant over the allele for black colour (b)
• Genotype


  The alleles an individual has
• Phenotype


  The characteristics that are produced, including what the individual looks like
• Green seed pod (G) is dominant to yellow seed pod (g)
• Monohybrid inheritance


  1. Parent genotypes

  2. Parent gametes

  3. Possible offspring genotypes

  4. Possible offspring phenotypes
• Cystic fibrosis (CF) is a genetic condition caused by a recessive allele
• Identical twins share the same genes so they are genetically identical. However, there may be small differences between identical twins, for example, in their body mass, due to environmental variables
• The Human Genome Project is a collaboration between scientists to decode the human genome (the order of bases in DNA)
• The Human Genome Project was completed quickly because so many scientists worked on it at the same time
• The results of the Human Genome Project are being used to develop new medicines and treatments for diseases
• Advantages of the Human Genome Project


  • Alerting people that they are at particular risk of certain diseases
  • Distinguishing between different forms of diseases
  • Allowing doctors to tailor treatments for some diseases to the individual
• Disadvantages of the Human Genome Project

  • People who are at risk of certain diseases may have to pay more to obtain life insurance
  • It may not be helpful to tell someone they are at risk of a condition for which there is currently no cure
• Humans all share the same genes, but think carefully about alleles and base sequences
• The Human Genome Project means that soon we might be able to tell a child that they are at increased risk of high blood pressure in early middle age