Meiosis

Or reduction division.

What is the Difference between

Mitosis and

Meiosis

Mitosis • Occurs in body

(somatic) cells

• 2n -> 2n• 46 to 46 (in Humans) • Diploid to Diploid • Goes through PMAT

once

Meiosis • Occurs in gonads to

make gametes (sex cells) sperm and egg

• 2n -> 1n

• 46 to 23 (in Humans)

• Diploid to Haploid

• Goes through PMAT twice

Meiosis

Independent Assortment

occurs during

anaphase 1 of Meiosis

Spermatogenesis• How a body makes sperm cells.

• Occurs in the testes

• One 46 chromosome cell becomes four

spermatids containing 23 chromosomes.

Oogenesis• Oogenesis makes oocytes. Egg=Oocyte

• Occurs in the Ovaries. (before birth)

• One cell containing 46 chromosomes becomes four cells containing 23 chromosomes. Three of the cells called Polar Bodies die.

• One Cell Survives and becomes an oocyte.

Asexual vs. Sexual Reproduction

• Asexual reproduction is the production of an offspring from one parent.– Budding (Jellyfish, Hydras, some Plants) – Binary Fission (bacteria) – Mitosis is used (no genetic difference from

parents)

• Sexual Reproduction is the production of an offspring from two parents. – Meiosis is used ( there is genetic variation

from parents)

Plants can send out runners that make new plants like this strawberry plant

Jellyfish during the

Polyp phase bud

Hydra Budding

P 156 1-6 1. List two ways that mitosis differs from meiosis. 2. During which stage of meiosis is the diploid

number of chromosomes reduced to the haploid number of chromosomes?

3. How many chromosomes do gametes normally contain?

4. Explain the role of crossing over to ensure genetic variation.

5. Describe the primary difference between spermatogenesis and oogenesis.

6. Explain why the chromosomes in haploid cells that are produced in meiosis I look different from those produced in meiosis II