Meiosis Notes Nowlets review chromosomes Steps of Meiosis

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

One major point! • Meiosis results in 4 genetically different haploid daughter cells *These cells are sperm and eggs!

Fertilization n + n = 2 n Haploid Egg cell Haploid Sperm cell Diploid Zygote 23 chromosomes 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?