Meiosis • Meiosis – germ cell go through 2 nuclear divisions that results in 4 daughter cells with half the number of chromosomes as the parent cell. – Explains how gametes are produced • daughter cells are not genetically alike. – may have different combination of genes • Sexually reproducing organisms are capable of combining chromosomes from 2 parents to produce offspring. • The chromosomes that combine during sexual reproduction are contained in reproductive cells called gametes. • • Control of the Cell Cycle http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__control_of_the_cell_cycle.html • • Activity: 25 point extra creditGo to the onion root tip activity and complete the percentages activity. http://www.biology.arizona.edu/Cell_bio/activities/cell_cycle/cell_cycle.html • • Mitosis Rap http://www.nclark.net/MitosisRap.mp3 • Mitosis Animation and Tutorial http://www.biology.arizona.edu/Cell_bio/tutorials/cell_cycle/cells3.html • http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html http://www.sumanasinc.com/webcontent/animations/content/mitosis.html • • • • Meiosis http://www.youtube.com/watch?v=D1_-mQS_FZ0 http://highered.mcgrawhill.com/sites/0072943696/student_view0/chapter19/animation__how_meiosis_works.html http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html# Mitosis vs Meiosis http://www.johnkyrk.com/meiosis.html http://www.pbs.org/wgbh/nova/baby/divide.html# http://www.pbs.org/wgbh/nova/baby/divi_flash.html • • http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__comparison_of_meiosis_and_mitosis__quiz_1_.ht ml Meiosis • like mitosis, meiosis follows Interphase and ends with cytokenisis • The 1st meiotic division results in two cells with ½ the number of chromosomes as the parent cell. • The 2nd meiotic division is like mitosis; the number of chromosomes does not get reduced. Results in 4 daughter cells with half the # of chromosomes as the parent cell Prophase I • each chromosomes consist of two sister chromatids connected at the centromere • Homologous pairs of chromosomes come together, this event is called synapsis • Each pair of homologous chromosomes is called a tetrad. (4 chromatids that make up a homologous pair) • Crossing over – exchange of genes between non- sister chromatids of a homologous pair • results in genetic recombination by producing a new mixture of genetic material. Metaphase I • Homologous pairs (tetrads) align in the middle of the cell. Anaphase I • homologous pairs separate and move to opposite ends of the cell. – Each chromosome consist of 2 chromatids Telophase I • Spindle fibers break down • 2 new nuclei form – One around each set of chromosomes – ½ the number of chromosomes as the original (parent) cells – End of Meiosis I Meiosis II Prophase II • Spindle fibers form Metaphase II • chromosomes line up at the equator Anaphase II • sister chromatids separate at the centromere and move to opposite poles ttp://highered.mcgrawhill.com/sites/0072943696/student_view0/c hapter19/animation__how_meiosis_works.h tml Telophase II • 4 new nuclei appear; one around each set of chromosomes • followed by cytokenesis • end up with 4 cells that are all haploid with only 1 chromatid for each chromosome • Review • http://www.biology.arizona.edu/cell_bio/tut orials/meiosis/problems.html Meiosis - Males Meiosis in Females • Meiosis II • prophase II: spindle fibers attach to the duplicated chromosomes and begin moving them to the spindle equator. • metaphase II: chromosomes align at the cell equator with one chromatid facing one pole and the other chromatid facing the opposite pole. • anaphase II: the chromatids separate and are now called chromosomes. The chromosomes migrate toward the two poles. • telophase II: the chromosomes arrive at the opposite poles, and the cytoplasm divides. The two meiotic divisions result in four haploid cells.