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Biology: Chapter 11-4 (Meiosis)
Transcript of Biology: Chapter 11-4 (Meiosis)
Homologous pairs associate
Crossing over can occur at chiasmas Metaphase I Crossing over also at prometaphase I
Bivalents (homologous pair) line up at the equator, two by two, random orientation of chromosomes
Spindle fibres attach to centromeres Anaphase I Telophase I Spindle fibres contract to pull chromosomes to opposite poles
Centromeres do not separate
One chromosome from each homologous pair moves to opposite ends of cell Cytokinesis Cleaving of the cytoplasm forms 2 diploid cells Prophase II No homologous pairs
No crossing over
Chromosomes condense again Metaphase II Chromosomes align singly & randomly
Spindle fibres attach to each centromere
Chromosomes are randomly orientated Anaphase II Telophase II New haploid nuclei form
Results in four haploid gamete cells Cytokinesis Cleaving of cells to form 4 daughter haploid cells
Haploid cells develop into gametes Interphase (Interkinesis) Organelles produced
No further DNA replication Mitosis Vs. Meiosis This is where mitosis and meiosis differ most significantly
Meiosis now undergoes a second nuclear division Crossing over/recombination: Chromosomes from your parents are randomly distributed into your gametes
Each new gamete can have all your maternal or all your paternal chromosomes or any combination of the two.
Crossing over in Prophase I
There are 2^23 possible orientations, a huge number of maternal and paternal chromosome combinations. Bibliography:
"Brent Cornell." 4.2 Meiosis. N.p., n.d. Web. 03 Mar. 2013. <http://ib.bioninja.com.au/standard-level/topic-4-genetics/42-meiosis.html>.
"TOPIC 3 The Voice of the Genome." Edexcel AS Biology. Harlow: Pearson Education, 2008. 158-59. Print.
Nature.com. Nature Publishing Group, n.d. Web. 03 Mar. 2013.
McDarby, Michael. "Introduction to Biology Molecules and Cells Chapter 7 - DNA, Genetics, and Reproduction." N.p., n.d. Web. 3 Mar. 2013.
"Cell Division, SEM Poster." Cell Division, SEM Poster. N.p., n.d. Web. 03 Mar. 2013.
Taylor, Steven. "4.2Â Meiosis." IBiology. N.p., n.d. Web. 03 Mar. 2013. <http://i-biology.net/ibdpbio/04-genetics-and-genetic-engineering/meiosis-inc-ahl/>. Chromatids break at chiasmatas
Exchange genetic information by breaking and recombining
Errors lead to mutation Non-disjunction Spindle fibres pull both chromosomes in homologous pair to one side
Results in two triseme cells, two monoseme cells Non-disjunction Spindle fibres pull both chromatids in chromosome to one side
Results in a triseme cell, a monoseme cell, and two normal cells Sister chromatids at poles
Nuclear membrane reforms
Cytoplasm begins to divide by cytokensis
Nuclei are no longer diploid
Each contain one pair of sister chromatids Spindle fibres contract and the centromeres are broken
Spindles pull sister chromatids to opposite poles
Cells remain haploid
If non-disjunction occurs, two gametes containing the wrong number of chromosomes will remain Co-Editors Synapsis: Fusion of the chromosomes MEIOSIS I MEIOSIS II Genetic Variation By Darria Inge Co-Editor #2 -Alisa Johnson Co- Editor #1- Brittaney Scruggs