1. 1 Meiosis

2. 2 To help you understand about DNA…. How is DNA passed from parent to offspring? There are two main ways that DNA is passed from parent to offspring:  1. Asexual reproduction – process by which a single parent reproduces by itself Mitosis is a form of asexual reproduction. In this process, the parent and offspring will be genetically identical. http://artfiles.art.com/images/-/Oxford-Scientific/Green-Hydra-Budding-Photographic-Print- C12940880.jpeg http://lifeboat.com/images/bacteria.jpg

3. 3  2. Sexual reproduction – process by which two cells from different parents unite to produce the first cell of the new offspring Meiosis is the process used to create genetically different gametes (sperm/eggs) used in sexual reproduction. In this process, the parents and offspring will be genetically unique. http://upload.wikimedia.org/wikipedia/commons/thumb/0/02/Mother_and_baby_Elephas_maximus.JPG/800px- Mother_and_baby_Elephas_maximus.JPG

4. 4 What is meiosis? Meiosis is a type of cell division that results in four genetically different haploid cells.  Diploid (2N) – a cell with ‘2 sets’ of chromosomes  Haploid (1N) – a cell with ‘1 set’ of chromosomes Meiosis is used to produce haploid gametes (sperm and eggs) in organisms that reproduce sexually. Human gametes:  In men, meiosis produces 4 equally sized sperm cells.  In women, meiosis produces 1 egg and 3 polar bodies that later disintegrate. http://www.emc.maricopa.edu/faculty/farabee/BIOBK/gametogen_2.gif

5. 5 The Phases of Meiosis The phases of meiosis are the same as the phases of mitosis, but in meiosis each phase occurs twice. Meiosis I includes Interphase I, Prophase I, Metaphase I, Anaphase I, and Telophase I, followed by Cytokinesis.  Meiosis I results in 2 haploid daughter cells. http://www.copernicusproject.ucr.edu/ssi/HighSchoolBioResources/Cell%20Division/Meiosis/Meio sis.asf

6. 6 Meiosis I In Prophase I, homologous chromosomes pair up and form a tetrad.  Homologous chromosomes – Refers to two similar chromosomes in a diploid cell. One chromosome is derived from the father gamete cell and the other from the mother  Crossing over – homologous chromosomes exchange pieces of DNA to produce genetically different gametes. This yields genetic variation which ultimately plays a role in evolution.

7. 7 A Sketch of Chromosomes Crossing Over (Prophase I) http://images.google.com/imgres?imgurl=http://www.phschool.com/science/biology_place/labbench/lab3/images/crossovr.gif&imgrefurl=http://www.phschool.com/science/biology_place/labbench/lab3/crossovr.html&h=320&w=240&sz=3&hl=en&start=11&tbnid=GqFKVxw1ZWYopM:&tbnh=118&tbnw=89&prev=/images%3 Fq%3Dcrossing%2Bover%2Bchromosomes%26gbv%3D2%26svnum%3D10%26hl%3Den%26safe%3Dactive%26sa%3DG

8. 8 Meiosis II Includes Prophase II, Metaphase II, Anaphase II, and Telophase II, followed by Cytokinesis. Each of the haploid daughter cells from Meiosis I divide again to make 4 haploid cells.

9. 9 Comparing Mitosis and Meiosis The processes of mitosis and meiosis are very similar, but with some important differences: Meiosis Includes 2 cycles of cell division (Meiosis I and Meiosis II) Occurs only in gametes (sex cells) Chromosomes cross over in Prophase I Results in four genetically different haploid cells Metaphase I: 2 duplicated chromosomes per spindle fiber Mitosis Includes only 1 cycle of cell division Occurs in body cells No crossing over of chromosomes Results in two genetically identical diploid cells Metaphase: 1 duplicated chromosome per spindle fiber