MEIOSISKatie Hughes, David Suarez, Abi Lawrence, Taylor Edwards and

Katelynn Granger

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

http://www.johnkyrk.com/meiosis.html

10.1.2 Outline the formation of chiasmata in the process of crossing over

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

http://www.sumanasinc.com/

webcontent/animations/

content/independentassortment.

html

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>.