From Egg to Embryo From Egg to Embryo – This photograph shows the After the egg [shown in orange] is released from the ovary, it travels into the fallopian tube. It stays there until a single sperm [shown in blue] fertilizes it. This unit will explain the process of meiosis in the production of eggs and sperm; summary color is blue and vocabulary words are underlined.

 Meiosis is the process by which the number of chromosomes is reduced by half forming gametes EX sperm or eggs.  Two cell divisions  Meiosis animation Meiosis animation ontent/uploads/2008/06/meiosisimagecreditnih.jpg

 Meiosis creates haploid cells; remember, you get half your DNA from each of your parents.  Haploid, n = a cell with only 1 copy of each chromosome; EX sex cells are haploid.  Mitosis creates IDENTICAL diploid cells.  Diploid, 2n = a cell with 2 of each chromosome; EX somatic [body] cells like skin cells or heart cells are diploid. "Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, Science in Context. Web. 3 Dec

How do the sketches to the right visually represent a diploid versus a haploid cell? Which is made by mitosis versus which is made by meiosis? Turn and talk to your neighbor. ploidDiploid.png

 The stages of meiosis I are identical to the stages of cell cycle and mitosis; there are only slight differences during prophase.  After going through the steps of Meiosis I 1. Interphase 1 2. Prophase 1 [+ crossing over] 3. Metaphase 1 4. Anaphase 1 5. Telophase 1 + Cytokinesis  Forms 2 diploid daughter cells.  …the cell divides again! [AKA Meiosis II] "Meiosis." Biology. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010.Science in Context. Web. 3 Dec

 AKA homologs are paired Xsomes with genes of the same trait in the same order; within each pair, one chromosome comes from each parent.  Homologous chromosomes are only found in a diploid cell. "Result of Crossing Over." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, Science in Context. Web. 3 Dec

This a karyotype, a tool that geneticists use to look for mutations. It groups the homologous chromosomes in pairs; the longest pair is #1, the shortest pair is #22. ges/karyotype.jpg

 During Prophase I, the homologous chromosomes mix genetic material [known as crossing over].  This is used to create new combinations of genes – when the cell is split in two, the genetic material is now different than the parent cell due to crossing over.  Allows for more variety within organisms.  Crossing Over Animation Crossing Over Animation mg/picture/242/crossing_over.jpg

How do the sketches to the right visually represent crossing over. Turn and talk to your neighbor.

 After meiosis I the cell divides again!  This stage is different yet again, because Xsomes are NOT copied during Meiosis II.  The stages are identical (interphase, prophase, metaphase, etc), but cells formed have half (haploid) of the number of Xsomes in the parent cells.  Forms unique 4 haploid daughter cells.  Meiosis Animation Meiosis Animation osis.gif/250px-Meiosis.gif

"Mitosis and meiosis." World of Anatomy and Physiology. Gale, Science in Context. Web. 4 Dec Name & Period at the Top What are the similarities and differences between the processes of mitosis and meiosis? List your answer in bullet points on your sticky note.

 Use the play dough and the chalk to show meiosis at your tables.  Our organism only has 2 chromosomes; use two colors [do not completely mix them].  Show the following:  Meiosis 1 Stages  Crossing over  Meiosis 2 Stages + Cytokinesis  Label the following:  Diploid cell  Haploid cell

How many chromosomes are at the beginning of the diagram versus at the end? Based on that information, how many would go in each haploid daughter cell? Turn and talk to your neighbor.

 During meiosis, if homologous chromosomes fail to separate correctly during anaphase (nondisjunction) then gametes have either extra Xsomes or they are missing chromosomes.  These mutations are passed on during fertilization [see image to the right].  Offspring with more than the usual # of Xsomes are called polyploids. ▪ Rare in animals, sometimes causes death. ▪ Common in plants; polypoids are often healthier.

One of the most common examples of polyploidy in humans is Trisomy 21 [extra copy of chromosome 21]. These individuals have Down syndrome. own_syndrome.jpg /glee/images/9/98/Becky_Jackson.png

How do the sketches to the right visually compare normal meiosis versus nondisjunction. Turn and talk to your neighbor. "Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, Science in Context. Web. 3 Dec