Genetics

• Meiosis: sexual reproduction creating human sex cells (gametes)

  • the cell makes copies of its chromosomes
  • cell division 1 divides into two cells, cell divison 2 divides into four cells
  • four genetically different haploid daughter cells are created
• DNA: found in the chromosomes of a nucleus

  • double helix structure containing four bases (adenine, thymine, cytosine & guanine) connected to a sugar-phosphate backbone.
  • bases are complementary and bonded by weak hydrogen bonds
• DNA:

  • a gene is a section of DNA that codes for a protein
  • a genome describes all the genetic info of a single organism
• Core practical:

  • homogonise cells by mashing up fruit
  • add soap, which breaks down the nuclear and cell membrane
  • add salt, which coagulates the DNA
  • add juice (protease), that breaks down proteins in the nuclear and cell membrane
  • filter to remove insoluble material
  • add ice-cold ethanol as it precipitates the DNA
• Protein synthesis: three bases code for an amino acid, which are joined together and fold to make a protein

  • in transcription, RNA polymerase binds to non-coding DNA which produces complimentary mRNA, that leaves the nucleus
  • in translation, at the ribosomes tRNA attatches to its codon which code for amino acids, they connect to form a polypeptide
• Genetic variants: a change in the order of bases affects the structure of proteins

  • a base is inserted, deleted or substituted
  • most mutations do not alter the protein but some can have serious effects such as the substrate will not fit into the active site
• Gregor Mendel:

  • experimented with breeding pea plants and concluded that characteristics are inherited from parents and units can be dominant or recessive
• Alleles: a different version of a gene

  • dominant alleles are expressed when only one allele is needed - can be homozygous or heterozygous
  • recessive alleles can only be expressed when homozygous
  • alleles lead to differences in inherited characteristics, which we can predict using punnet squares and pedigree charts
• Offspring sex:

  • females have XX chromosomes, whereas males have XY chromosomes
  • sex chromosomes can have alleles which cause a sex-linked genetic disorder - these are found on the X chromosome (X^D)
• Blood groups:

  • A and B blood types are dominant and can be codominant
  • O blood types are recessive, and are extremely rare
• Variation: between individuals allows natural selection to occur

  • genetic variation is caused by sexual reproduction or gene mutations
  • environmental variation is caused by the environment
• Human genome project:

  • improved understanding of genes linked to disease
  • helped the treatment of inherited disorder
  • tracing human migration patterns from the past