DNA and genetics
DNA is a polymer of nucleotides (sugar, phosphate, base). A gene is a short section of DNA that codes for a protein. Chromosomes are in the nucleus. Gametes are haploid; fertilisation restores the diploid number.
Meiosis produces four non-identical haploid gametes. Genetic diagrams (Punnett squares) predict offspring ratios. Dominant alleles are expressed if present; recessive alleles need two copies. Sex chromosomes: XX female, XY male.
Variation and evolution
Variation is genetic, environmental, or both. Mutations change DNA; most have no effect, some influence phenotype. Natural selection: individuals with advantageous phenotypes are more likely to survive and breed, so the allele becomes more common.
Selective breeding chooses parents with useful characteristics. Genetic engineering transfers genes, for example insulin production or GM crops. Speciation can occur when populations are isolated and natural selection acts differently.
Classification
The three-domain system groups organisms as Archaea, Bacteria and Eukarya, based on genetic evidence as well as physical features.
Taught with support from Joseph Danso, Science Lecturer in London. Book a session.