Biology (DNA and inheritance)

• DNA


  Deoxyribonucleic acid, a double-stranded polymer of nucleotides that form a double helix
• DNA


  • T-A (thymine always pairs with adenine)
  • C-G (cytosine always pairs with guanine)
  • Base pairing rule
• Triplet code = 1 amino acid
• Genetic profiling


  1. Sample of cells collected

  2. DNA extracted from cells

  3. DNA sample cut into fragments using enzymes

  4. Fragments separate into bands creating a genetic profile
• Genetic engineering


  The modification of the genome of an organism by insertion of a desired gene from another organism
• Genetic engineering


  • Benefits: Increased crop yields, Used in medicine, Produce scarce resources, Produce oils for biofuels
  • Risks: Unknown long-term effects, Negative environmental impacts, Expensive, Could become pests, Ethical issues
• Monohybrid inheritance = the inheritance of a single gene 


  1. H-dominant

  2. h-recessive
• Sex determination in humans

  • Males have X+Y chromosomes
  • Females have X+X chromosomes
  • Meiosis produces gametes with half the number of chromosomes
  • Sex depends on what sperm fertilises the egg
• Protein synthesis


  1. The gene is copied as mRNA

  2. The mRNA copy of the gene goes into the cytoplasm

  3. The mRNA code is read by a ribosome which links the correct amino acids to make a protein
• selfing = an artificial method of self-pollinating plants
• F2 generation = 2nd generation in a genetic cross
• F1 generation = 1st generation in genetic cross, the offspring produced when 2 organisms inbreed
• phenotype = how the genotype shows its self eg blue eyes
• genotype = an organisms genetic composition (alleles) BB
• heterozygous = having two different alleles of a gene eg Gg
• homozygous = having 2 identical alleles of a gene eg gg
• recessive = an allele that is only expressed in the absence of a dominant allele
• dominant = an allele that is always expressed
• gamete = reproductive cells that contain a single copy of each chromosome
• allele = a variety of a gene
• gene = length of a DNA that codes for a particular protein