Section 10.2

• Diploid – Normal cell with 2n number of chromosomes from either parent organism

• Haploid – only one kind of chromosome (n). These cells are gametes usually.

• Homologous chromosomes – chromosomes that determine the phenotype of an organism's cells that will have the same genes for a trait but not in the same order, necessarily.

• If sex cells had the number of chromosomes that a normal cell has, the amount of chromosomes would increase over time. This is why meiosis occurs.

• Meiosis Cycle, easy way to remember:

  • Prophase (Please) – Spindle fibers form, tetrads form, crossing over may occur

  • Metaphase (Make) – Tetrads attach to spindle fibers, move to equator

  • Anaphase (Another) – Tetrads split into double stranded chromosomes and move to opposite ends

  • Telephase (Taco) – Spindle breaks down, chromosomes uncoil, cytoplasm divides

• Meiosis II = EXACTLY THE SAME EXCEPT: It yields 4 gametes instead of two normal cells.

• 70 TRILLIAN different combinations, excluding genetic crossover.

• Genetic recombination – basically, genetic crossover

• Nondisjunction – failure of chromosomes to separate during meiosis

• Trisomy – when an gamete with an extra chromosome fuses with a normal gamete

  • Many organisms with extra chromosomes will survive

• Monosomy – when a gamete misisng a chromosome fuses with a normal gamete

  • Organisms will not survive monosomy most of the time, but Turner syndrome, where females have only one X chromosome, is one non-lethal example

• Triploid – organism has three sets of chromosomes

• Tetraploid – organisms has four sets of chromosomes

• Polyploids – organisms with more than the usual number of chromosome sets

  • Animals that are polyploidal almost always die

  • Polyploidal plants usually will survive with unique characteristics, such as enlarged size and greater health.

  • Plant breeders have learned how to cause polyploidal conditions in plants using chemicals