Meiosis

• Haploid: (n) refers to cells or organisms with only one set of chromosomes per cell and Diploid: (2n) refers to cells or organisms with only two sets of chromosomes per cell
• Homologous Chromosomes: Chromosome pairs that determine the same characteristics; one of each is inherited from each parent, may not be identical since the alleles (alternative forms of a gene) could differ
• Gene: A short section of DNA that codes for a specific polypeptide, it’s location on its chromosome is called Gene locus
• Crossing-over: Process by which DNA exchange occurs, where chromatid breaks during the prophase of meiosis I and rejoins to a non-sister chromatid of its homologous chromosome
• Nuclear division that occurs in the reproductive organs to produce gametes, it involves a halving of the chromosome number so daughter cells contain a haploid chromosome number compared with the parent cell (the diploid number)
• Halving of the chromosome number is important so that the diploid number can be restored during fertilisation, each parent cell divides to form 4 genetically different gametes (meiosis a source of genetic variation)
• Variation is important to the population as it is the raw material for natural selection and evolution, sources of variation in meiosis:

  1. Crossing over (prophase I)
  2. Independent assortment (metaphase I)
  3. Random fertilization (which sperm, which egg)
  4. Random mating (which people)
  5. Mutations
• Random fertilization: In sexual reproduction, the nuclei of two haploid gametes must fuse to restore the diploid number of the zygote, this fusion of gametes is completely random so adds to genetic variation within a population
• Mutations: DNA mutation may occur during DNA replication preceding mitosis and meiosis and chromosome mutations during mitosis or meiosis; the mutated gamete involved in fertilisation will be present in every body cell
• Spermatogenesis: Only have 1/2 the DNA; so they don’t divide themselves, as this would decrease the amount of genetic variation, still starts with a diploid cell

  A) Diploid

  B) 46

  C) 23

  D) 23

  E) 23

  F) 23

  G) 23

  H) 23