Genetics

• Chromosomes


  Thin strands of DNA sub-divided into functional genes
• Chromosomes

  • Located in pairs
  • Humans have 46 chromosomes (23 pairs)
  • Gametes don't have pairs
• Nucleus


  Where chromosomes are located
• Genome


  The entire genetic material of an organism
• Alleles


  Different forms of the same gene
• DNA


  Large and complex molecules that carry genetic code
• DNA bases


  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• DNA base pairing

  • C-G are complementary
  • T-A are complementary
• Phenotype


  Physical characteristics
• Genotype


  Genetic makeup represented by paired alleles
• Alleles


  • Versions of the same gene
• Dominant allele


  Always expressed, even if only one copy is present
• Recessive allele


  Only expressed if there are two copies present
• Homozygous alleles


  Both alleles are the same for a characteristic
• Heterozygous alleles


  Both alleles are different for the same characteristic
• DNA and chromosomes exist in cells
• Formation of Chromosomes 


  1. DNA copies itself

  2. DNA coils and condenses to form chromosomes
• Each chromosome is made from a single molecule of DNA
• A section of DNA contains a gene that codes for a particular protein
• Females have XX Chromosomes
• Males have XY
• Punnet squares

  help calculate the probability of an offspring inheriting different traits.
• Mendels Pea Plant Experiment

  1. Crossed a tall pea plant with a dwarf pea plant - offspring were tall
  2. crossed two two offspring- produced 3 tall and one dwarf
• Human genome project

  • Maps 3.3 billion comp base pairs in one set of 46 chromosomes
  • 99% of base pairs in different people are the same
  • helps show risk of different people developing diseases
  • can identify which medicines work best as alles affect how medicines work
• Meiosis

  Produces 4 haploid daughter cells, or, gametes which become diploid during fertilisation
• Protein Synthesis


  1. Transcription

  2. Translation
• DNA


  The code for proteins
• Transcription


  DNA code is copied into mRNA
• Translation


  mRNA code is used to direct the synthesis of proteins
• mRNA moves from the nucleus to the ribosome
• Ribosomes use the mRNA code to direct the synthesis of proteins
• Transfer RNA (tRNA) brings amino acids to the ribosome in the correct order to build the protein
• Protein synthesis involves the assembly of amino acids into a polypeptide chain
• The DNA code remains in the nucleus, while mRNA carries a copy of the code to the ribosome
• Extracting DNA from fruit

  A practical to demonstrate that cells contain DNA
• Extracting DNA from fruit

  1. Mash strawberries

  2. Put in beaker with detergent and salt solution

  3. Mix well

  4. Filter mixture

  5. Add ice-cold alcohol

  6. DNA precipitates as stringy white solid
• Detergent

  • Breaks down cell membranes to release DNA
• Salt

  • Makes the DNA stick together
• Cold alcohol

  • DNA is not soluble in, causing it to precipitate out
• Fruit

  • Strawberries