Topic 6: inheritance, variation and evolution

• Protein synthesis


  The process of making proteins
• Protein synthesis


  1. Transcription

  2. Translation
• Transcription


  The process of taking a single gene of DNA and copying it into a structure called mRNA
• Translation


  The process of taking the mRNA strand and using it to produce a protein
• Inside almost every cell is a nucleus that contains all the genetic material of that cell in the form of DNA
• DNA contains thousands of genes which are each small sections of the DNA that have a specific sequence of bases and so are able to code for a specific sequence of amino acids which when combined will form a particular protein
• DNA is so big it can't leave the nucleus itself
• mRNA


  A copy of a single gene, a messenger RNA
• mRNA


  • It is much shorter than DNA because it's only a single gene long
  • It is a single strand rather than a double strand like DNA
  • Instead of containing the base thymine it contains uracil
• Transcription


  1. RNA polymerase binds to the DNA just before the gene starts

  2. The two strands of DNA separate apart so all their bases are exposed

  3. RNA polymerase reads the DNA bases one by one and uses them to make an mRNA strand

  4. The mRNA bases are complementary to the DNA bases

  5. RNA polymerase detaches from the DNA once it has finished making the mRNA strand
• Template strand


  The DNA strand that the RNA polymerase moved along to make the mRNA
• Codon


  A group of three bases that codes for a specific amino acid
• Cells use 20 different amino acids and each one has a different three base codon
• Translation


  1. mRNA and ribosome bind together

  2. Ribosome adds one amino acid at a time to build the protein chain

  3. tRNA molecules bring the correct amino acids to the ribosome based on the mRNA codons

  4. Ribosome moves along the mRNA, joining the amino acids together

  5. Once the full chain is built, it detaches from the ribosome and folds up to form the final protein
• tRNA


  Transfer RNA, molecules that bring the amino acids to the ribosome based on the mRNA codons
• Anticodon


  The three base sequence on tRNA that is complementary to the codon on mRNA
• Genetic diagram


  Diagram that shows the different combinations of alleles that can be inherited from two parents
• Allele


  • Uppercase letter represents dominant allele
  • Lowercase letter represents recessive allele
• Homozygous


  Having two identical alleles for a particular trait
• Heterozygous


  Having two different alleles for a particular trait
• Phenotype


  The observable physical or biochemical characteristics of an organism
• Genotype


  The genetic makeup of an organism
• Drawing a genetic diagram

  1. Find parents' phenotype and genotype

  2. Find gametes' genotypes

  3. Find offspring's genotypes

  4. Find offspring's phenotypes
• Genetic diagram example


  • Normal mouse (AA) x Muscular mouse (aa)
  • Offspring genotypes: Aa, Aa, Aa, Aa
  • Offspring phenotypes: All normal
• Normally many different genes interact to determine a trait, and the environment can also play a big part
• Family tree


  Also called a family pedigree
• Cystic fibrosis


  A recessive inherited disorder
• Recessive allele


  Represented by lowercase 'f'
• Dominant allele


  Represented by uppercase 'F'
• Homozygous recessive genotype


  Two lowercase 'f' alleles
• Homozygous dominant genotype


  Two uppercase 'F' alleles
• Heterozygous genotype


  One uppercase 'F' and one lowercase 'f' allele
• Family pedigree symbols


  • Circles represent females
  • Squares represent males
  • Unshaded shapes = no condition
  • Shaded shapes = have condition
  • Half-shaded shapes = carrier
• Determining genotype from family pedigree

  1. Homozygous recessive = disease

  2. Heterozygous = carrier

  3. Homozygous dominant = unaffected
• Generations in family pedigree

  • Top row = parents
  • Second row = children
  • Bottom row = grandchildren
• Horizontal lines between individuals


  Indicates they are a couple
• Sam, Ryan, and Jack are unrelated individuals from different families, but are shown as they are partners of members of the main family
• Jenny is an unaffected female, so has the homozygous dominant genotype 'FF'
• Paul is a male carrier, so has the heterozygous genotype 'Ff'
• Anna and Lucy are carriers, with the heterozygous genotype 'Ff'