meiosis

• Meiosis

  The process by which gametes (sperm and egg cells) are produced, with half the normal number of chromosomes
• Chromosomes in gametes


  • Single, not paired
• Meiosis


  1. Chromosomes are copied

  2. Cell divides into two

  3. Both cells divide one more time forming gametes
• Fertilization


  The joining of a male gamete (sperm) and a female gamete (egg) to form a new cell with the full number of chromosomes
• After fertilization, the new cell has 23 chromosome pairs
• After fertilization


  1. New cell divides by mitosis

  2. Produces a clump of identical cells (embryo)

  3. Cells differentiate to form different cell types
• Chromosome number

  Humans have 46 chromosomes in body cells, sperm and egg cells have 23 chromosomes
• Meiosis(Chromosomes)

  Reduction division, starting cell has 46 chromosomes, ending cells have 23 chromosomes
• Meiosis

  • Only takes place in sex organs
  • Produces haploid gametes (not diploid cells)
• Fertilization


  Gametes fuse to produce a diploid zygote
• Gametes produced by meiosis are genetically different
• Homologous chromosomes


  Chromosome pairs where one chromosome comes from each parent
• Homologous chromosomes have the same genes but can have different alleles
• Crossing over in meiosis is a major source of genetic variation
• Meiosis produces four genetically different haploid gametes from one diploid cell
• Meiosis


  A process that contributes to genetic variety, makes sperm and egg cells (gametes)
• Chromosome number


  Humans have 46 chromosomes in most body cells, but sperm and egg cells have 23 chromosomes each
• Meiosis


  Reduction division, starting cell has 46 chromosomes, ending cells have 23 chromosomes
• Interphase


  Cell grows, replicates DNA, carries out processes, happens before meiosis starts
• Homologous chromosomes


  Approximately the same size, contain the same types of genes in the same locations
• Crossing over


  Chromosomes in homologous pairs exchange genetic information, creates recombinant chromosomes
• Crossing over in meiosis

  1. Homologous chromosomes come together
  2. Chromatids wrap around each other
  3. Parts of chromatids can break off and exchange
  4. Results in recombinant chromosomes