Meiosis Honors Biology Spring 2013

Warm-Up With a neighbor, discuss the following: What is meiosis? How does it differ from mitosis?

Essential Questions What is meiosis and why is it necessary? What are the stages of meiosis? How does meiosis compare to mitosis?

Haploid vs. Diploid Diploid cells 1. Body cells 2. Contains homologous chromosomes 3. 2N B. Haploid cells 1. Sex cells 2. contains one member of each pair 3. 1N

Meiosis Meiosis process which reduces by half the number of chromosomes in a diploid cell meiosis occurs in sex organs of individual

Overview of Meiosis A. Meiosis - formation of sex cells 1. Meiosis is cell division that results in a gamete containing half the number of chromosomes of its parent. 2. Meiosis includes 2 steps that each closely resemble corresponding steps in mitosis.

Phases of Meiosis meiosis I Prophase I Metaphase I Anaphase I Telophase I &? Cytokinesis PMAT I Meiosis II Prophase II Metaphase II Anaphase II Telophase II &? Cytokinesis PMAT II

Meiosis 1 Meiosis I - reduction division 1. Interphase I 2. Prophase I 3. Metaphase I 4. Anaphase I 5. Telophase I

Meiosis 1: Prophase 1 chromatin condenses to form chromosomes homologous chromosomes attach to form tetrads

Meiosis 1: Prophase 1 when tetrads form, crossing over can occur crossing over is the exchange of part of homologous chromatids

Meiosis 1: Metaphase 1 tetrads line up on equator spindle fibers attach to centromeres

Meiosis 1: Anaphase 1 homologous chromosomes separate spindle fibers pull them to opposite poles

Meiosis 1: Telophase and Cytokinesis telophase I nuclear membrane reforms cytokinesis cytoplasm splits

Meiosis 1: Results results two haploid (n) daughter cells = ½ the number of chromosomes as parent cell

Meiosis II Meiosis II - separation of chromatids 1. Interphase II 2. Prophase II 3. Metaphase II 4. Anaphase II 5. Telophase II

Meiosis II: Prophase II chromosomes already formed

Meiosis II: Metaphase II chromosomes line up along equator

Meiosis II: Anaphase II sister chromatids separate move to opposite ends

Meiosis II: Telophase and Cytokinesis telophase II nuclear envelope reforms cytokinesis cytoplasm splits

Meiosis II: Results 4 haploid (n) daughter cells all genetically different

Ploidy parent cell? dipliod (2n) after meiosis I? haploid (n) (monopliod) after meiosis II? hapliod (n)

Purpose of Meiosis: Diversity Meiosis and sexual reproduction significantly contribute to genetic variation among offspring.

Purpose of Meiosis: Gametes role of meiosis is to produce gametes meiosis in males spermatogenesis produces 4 sperm cells meiosis in females oogenesis produces 1 ovum (egg cell) and 3 polar bodies

Where Does Meiosis Occur?

Mitosis vs. Meiosis where does is occur? number of cell divisions? meiosis – sex organs; mitosis – somatic cells number of cell divisions? meiosis – 2; mitosis – 1 number of cells produced? meiosis – 4; mitosis – 2 ploidy of daughter cells? meiosis – hapliod (n); mitosis – dipliod (2n) # of chromosomes compared to parent cell? meiosis – ½ # chromosomes; mitosis – same

Mitosis vs. Meiosis