Meiosis vs. Mitosis

Mitosis• Cell division• 46 chromo2 cells, 46 chromo. Each• Keeps chromo. # same• Found in body cells• Most common• No genetic variation

Meiosis• Cell division• 46 chromo 4 cells, 23 chromo each• Chromo. # cut in half• Found in sex/germ cells

ONLY• Least common• Most genetic variation

ANIMATION OF COMPARISON

ANIMATION 2 OF COMPARISON

I. Mitosis vs. Meiosis

II. ChromosomesKaryotypes:

• Display of chromosomes lined up in homologous pairs

• Half inherited from male Half from female

• Used for viewing #, size, shape, and banding patterns of chromosomes

Homologous Chromosomes:matching pair of chromosomes, one

inherited from each parent

Body cells/Somatic Cells= “Diploid”or 2N having two sets of chromosomes, body cells Humans 46 chromosomes

Sex cells/Sperm + Egg= “Haploid”or Nhaving one set of chromosomes, sex cells ( gametes) Ex: Humans 23 chromosomes

• Fertilization: when haploid sperm and egg meet, combining N

chromosomes with N chromosomes = 2N zygote

• Zygote: fertilized egg, 2N

____ ____ ____23 23 46

sperm egg zygote

Diploid vs. Haploid Exercises

• Drosophilia have a diploid number of 8. What is the haploid?

• Onions have a haploid number of 8. What is the 2N?

• A horse’s 2N is 64. What is the 1N?• A body cell of an alligator has 32

chromosomes. Is this the diploid or haploid number?

4

16

32

Diploid

II. Meiosis• Definition: cell division to produce egg (ovule) or

sperm (pollen)

Meiosis I & Meiosis II

Oogenesis: Production of Egg

• Female meiosis in the ovaries

• Resulting cells: 1 egg, 3 polar bodies• Haploid

Spermatogenesis:Production of Sperm

• Male meiosis in testes

• Resulting cells: 4 haploid sperm

cells

Animation spermatogenesis

Meiosis I (PMAT I & C)

• Prophase I: homologous chromosomes meet up and form tetrads. Crossing over occurs.

• What is the point of crossing over?

Meiosis II (PMAT II & C)

• What if Meiosis did not occur?