Meiosis Notes

Now…let’s review chromosomes!

Steps of Meiosis:• Meiosis is made of two parts: Meiosis I and Meiosis

II• First: BEFORE meiosis occurs, there is the “IN

BETWEEN PHASE”• Before Meiosis = INTERPHASE• First Part: Meiosis I!• Prophase I (CROSSING OVER OCCURS HERE!)

• Metaphase I• Anaphase I (HOMOLOGOUS CHROMOSOMES ARE SEPARATED)

• Telophase I• Cytokinesis

Steps of Meiosis:• Second Part: Meiosis II!

• Prophase II • Metaphase II• Anaphase II (SISTER CHROMATIDS ARE SEPARATED)

• Telophase II• Cytokinesis

Prophase 1

• Chromosomes become visible and the nuclear membrane breaks apart

• Crossing over occurs!

• Creates new gene combinations!

Metaphase 1 vs. 2

• Metaphase 1- homologous chromosomes pair up in the middle

• Metaphase 2- single chromosomes line up in the middle

Anaphase 1 vs. 2

• Anaphase 1- homologous chromosomes separate and move apart

• Anaphase 2- Chromatids separate and move apart

Telophase 1 vs. 2

• Telophase 1- Single cell splits into 2 cells, goes right into Prophase 2

• Telophase 2- Two cells each split, creating 4 haploid cells

Meiosis: A Second

Look

• Meiosis results in 4 genetically different haploid daughter cells

One major point!

*These cells are sperm and eggs!

Fertilization

n n+ = 2n

Haploid Egg cell

23 chromosomes

Haploid Sperm cell

23 chromosomes

DiploidZygote

46 chromosomes

Questions:What are some similarities between MITOSIS

and MEIOSIS?What are some differences between MITOSIS

and MEIOSIS?Why do organisms need to go through

mitosis?Why do organisms need to go through

meiosis?Which organisms undergo mitosis?Which organisms undergo meiosis?

Prove You Know It!1.What is the name of the

process that creates gametes?2.What is the difference

between a HAPLOID cell and a DIPLOID cell?

3.What are the two main parts of meiosis?