Post on 28-Dec-2015
Meiosis
4.2.1: State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei.
Called reduction division because the daughter cells have only half of the number of chromosomes as the parent cell
Purpose: To produce gametes to facilitate sexual reproduction
Result: Four haploid cells OVERVIEW: http://highered.mcgraw-hill.com/sites/
0072495855/student_view0/chapter28/animation__stages_of_meiosis.html
Meiosis
Spilt into 2 parts: Meiosis I
Prophase Metaphase Anaphase Telophase
Meiosis II Prophase Metaphase Anaphase Telophase
Important definitions
Haploid-a cell having half the number of chromosomes than a somatic cell
Somatic cell- normal body cell gamete- sex cell (sperm or egg cell) Chiasmata-the site at which crossing
over takes place. The process of crossing over
Meiosis I Interphase
Cell growth and DNA replication (review--before meiosis I) Prophase I
Chromosomes condense Homologous chromosomes pair up and crossing over
occurs (the point of cross over is known as the chiasmata) Nuclear membrane disintegrates and the centrioles travel
to the poles of the cell
Metaphase I Microtubules form a spindle and the spindle
fibers attach to the centromeres of the chromosomes
Pairs of homologous chromosomes align along the metaphase plate
Anaphase ISpindle fibers shorten and pull paired
chromosomes in opposite directions Paired homologous chromosomes
separate and pulled to opposite poles (sides) so that each pole contains one chromosome of each pair.
Telophase I A nuclear membrane forms around the
chromosomes at each pole and chromosomes uncoil Spindle fibers disintegrate The cell undergoes cytokinesis to form two daughter
cells (two haploid cells) At the end of telophase I the cells may enter a short
interphase period or proceed directly to meiosis II DNA is not replicated
Meiosis II
Mostly the same!!! Except this time it involves half the number of chromosomes as Meiosis I
Prophase II No crossing over (chiasma)
Metaphase II SAME
Anaphase II Separation of sister chromatids, instead of homologous chromosomes
Telophase II SAME
RESULT: FOUR HAPLOID DAUGHTER CELLS.
http://www.phschool.com/science/biology_place/biocoach/meiosis/mei2ani.html
Chiasmata New combinations of genes within
chromosomes are possible through this process
Can occur between any non-sister chromatids During prophase I, chromatids are close
together, so parts of each chromatid overlap, break at the chiasmata and reattach to the other chromatid
Sister chromatids a, b, c and d (b and c end up as new combinations called recombinants
Meiosis
10.1.3 Explain how meioisis results in an effectively infinite genetic variety in gametes through crossing over in prophase I and random orientation in metaphase I
The number of chiasmata, or points of crossing over, can differ…..infinite variety!!
Mendel’s Law of Independent Assortment
10.1.4 States that any one of a pair of
characteristics may combine with either of another pair.
So, two characteristics must be on different chromosomes
Since any combination of chromosomes is possible in metaphase I, any one pair of characteristics may combine with either of another pair
Mitosis V. Meiosis
Takes place within somatic (body) cells
Results in 2 daughter cells
Mother cell can be haploid of diploid
Is preceded by a S-phase No homologous pairing of
chromosomes Genotype of daughter
cells are identical to mother cells
•Takes place within gametes (sex cells)•Results in 4 haploid gametes•Mother cell is diploid•Only meiosis I preceded by a S phase•During prophase I, homologous chromosomes pair up•Meiotic products differ in their genotype from the mother cell
WORKS CITEDWorks Cited
"Chromosomes Crossing Over." Sciencelearn. University of Waikato, 8 June 2011. Web. 14 Feb. 2012. <http://www.sciencelearn.org.nz/Contexts/Uniquely-Me/Sci-Media/Images/Chromosomes-crossing-over>.
Farabee, M.J. "CELL DIVISION: Meiosis..." Estrella Mountain Community College. 18 May 2010. Web. 10 Feb. 2012. <http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookmeiosis.html>. Griffiths, Anthony J. F. An Introduction to Genetic Analysis. New York: W.H. Freeman, 2000. Print.
Hill, McGraw. "Stages of Meiosis." Highered.mcgraw-hill.com. McGraw Hill. Web. 10 Feb. 2012. <http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of %20Meiosis>.
"IB Biology Notes - Meiosis." IB Guides - Free International Baccalaureate Study Guides, Notes, Videos and Powerpoints. Web. 10 Feb. 2012. <http://www.ibguides.com/biology/notes/meiosis>.
Khara, Kanika. "Difference Between Mitosis and Meiosis." Buzzle Web Portal: Intelligent Life on the Web.
Buzzle. Web. 14 Feb. 2012. http://www.buzzle.com/articles/difference-between-mitosis-and-meiosis.html. Kyrk, John. "Meiosis = Double Cell Division." Communicating at an Unknown Rate. 2012. Web. 14 Feb. 2012. <http://www.johnkyrk.com/meiosis.html>.
Peeters, Weem Minka., Christopher Talbot, and Anthony Mayrhofer. Biology. Melton: Ibid, 2007. Print. "Phases of Meiosis | Biology." Khan Academy. Web. 10 Feb. 2012.
<http://www.khanacademy.org/video/phases-of-meiosis?topic=biology>.