Biology-DNA and inheritance

• Base pairs
• DNA molecule


  • The shape is a 'double helix'
  • Similar to a twisted ladder
• DNA structure


  1. Two long chains of alternating sugar and phosphate

  2. Connected by bases

  3. Bases form the 'rungs' of the ladder structure
• Types of bases


  • A (adenine)
  • T (thymine)
  • C (cytosine)
  • G (guanine)
• Complementary base pairing


  • A bonds with T
  • C bonds with G
• Order of bases


  Forms a code for making proteins
• Three bases


  Codes for one amino acid
• Triplet codes


  • AAT
  • CAG
• Triplet code


  Identifies a particular amino acid
• Triplet codes in the cytoplasm


  1. Used to identify amino acids

  2. Amino acids link together to form proteins
• Genetic profiling


  Uses the section of DNA that is individually unique
• Only identical twins share the same DNA
• Producing a genetic profile


  1. Taking a sample of DNA

  2. Extracting the DNA from the sample

  3. Cutting the DNA into short pieces

  4. Passing an electric current through the DNA

  5. Separating the DNA into bands
• Genetic profiles


  Can be compared to show the similarity between samples
• Uses of genetic profiles


  • Criminal cases
  • Paternity cases
  • Comparisons between species when they are being classified
• Gene


  A section of DNA
• Inherited feature


  Determined by single genes, such as eye colour
• Allele


  A form of a gene
• Alleles for eye colour


  • Blue
  • Brown
• Genes and alleles


  • Found in pairs
  • A pair of alleles controls a feature
  • One allele is inherited from your mother, the other from your father
• Homozygous condition


  The two alleles are the same
• Heterozygous condition


  The two alleles are different
• Genotype


  The genetic make-up of an individual
• Phenotype


  How the genotype shows itself, usually how a living thing appears
• Dominant allele


  Will always show itself, even if there is only one dominant allele present
• Recessive allele


  Hidden if the dominant allele is present
• Gamete


  A sex cell, in animals the gametes are sperm and egg cells
• Chromosome


  A linear arrangement of genes
• Benefits of genetic profiling


  • Identifying the presence of a certain gene that may be linked to a particular disease
  • Allowing preventative treatments or surgery that stops the disease or condition from developing
• Ethical issues of genetic profiling


  • Concerns about DNA being stolen or accessible to others
  • Stored DNA data getting into the hands of insurance, loan companies or employers who could analyse your DNA for the likelihood of disease and refuse you insurance or employment
• Possible genotypes


  • BB-homozygous dominant-brown eyes
  • Bb-heterozygous - brown eyes
  • bb-homozygous recessive - blue eyes
• Punnett square diagram


  Shows how two brown eyed parents can produce a blue-eyed child
• Chromosomes in human body cells


  • 23 pairs
  • Sex chromosomes are one pair of these chromosomes
  • Carry genes that determine sex of offspring
• Sex chromosomes at fertilization


  Separate and combine randomly