3 - Genetics

• A disadvantage of sexual reproduction is that

  • It requires gametes to fuse which takes longer and can't reproduce in isolated environments.
• An advantage of sexual reproduction is that

  • It produces genetically diverse offspring, allowing natural selection and the offspring can survive environmental changes
• An advantage of asexual reproduction is that

  • It produces many offspring meaning niches can be filled quickly
• A disadvantage of asexual reproduction is that

  • It produces genetically identical offspring and they are vulnerable to environmental changes
• Meiosis occurs in the gonads (testes and ovaries)
• In DNA extraction

  • Add protease enzymes to remove the proteins DNA is wound around so it's more visible.
  • Add ethanol to make the DNA precipitate out of the solution
• Why is protein synthesis required?

  • Bases have to be read by ribosomes outside of the nucleus To produce a protein from DNA
  • DNA can't leave nucleus as its too big
  • mRNA produced is only one gene long and smaller than DNA.
  • Has Uracil instead of Thymine
• Process of transcription:

  • DNA is unzipped
  • RNA polymerase binds to DNA strand.
  • It produces a mRNA strand complementary to the base sequence on the template strand. (With U instead of T)
  • The completed mRNA exits through a pore in the nucleus and heads to a ribosome.
• Process of translation:

  
  

  • mRNA attaches to ribosome
  • Each codon (3 bases) on mRNA complementary base pairs to an anticodon on the tRNA molecule
  • tRNA molecules have a specific amino acid attached.
  • This process repeats with the next codons.
  • A peptide bond forms between the amino acids, which continues until a stop codon is reached.
  • This amino acid chain is called a polypeptide
  • The polypeptide folds into a specific shape forming a protein
• A genetic mutation is any change in the sequence of bases

  A base is inserted into the code

  ● As they are read in threes, this changes the way it is read.

  ● It may change all the amino acids coded for after this insertion.

  A base is deleted from the code

  ● Like insertions they change the way it is read.

  ● It may change all the amino acids coded for after this deletion.

  A base is substituted

  ● This will only change one amino acid in the sequence or it may not change the amino acid (as the new triplet may code for the same amino acid)
• A mutation in the non coding region could mean RNA polymerase doesn't bind, meaning no transcription and the structure of the protein formed is affected.
• Codominance is when neither allele is dominant and both are expressed in the phenotype.

  IA and IB are codominant, while IO is recessive.

  Genotype IBIO is blood group B

  Genotype IAIB is blood group AB
• With X linked characteristics, a male cannot be a carrier but either have the disease or not.
• Advantages of human genome project:

  • Identification of new genes
  • Identification of new drug targets, for more effective treatments
  • Personalised medicines produced
  • Understand evolution
• Disadvantages of Human Genome Project:

  • Stress that something may occur - pressure to terminate pregnancies
  • Embryo can't consent to be tested
  • Designer babies with chosen characteristics (e.g eye colour)