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Meiosis. Formation of Sex Cells. Meiosis. A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Diploid – 2 sets of chromosomes Haploid – 1 set of chromosomes

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meiosis

Meiosis

Formation of Sex Cells

meiosis1
Meiosis
  • A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
  • Diploid – 2 sets of chromosomes
  • Haploid – 1 set of chromosomes
  • Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent
meiosis stages
Meiosis Stages
  • Meiosis usually involves 2 distinct stages
    • Meiosis I
    • Meiosis II
prophase i
Prophase I
  • Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
  • Each tetrad is made of 2 chromosomes, each with a copy attached forming sister chromatids
  • The pairing of homologous chromosomes is the key to understanding meiosis.
  • Crossing-over may occur here
  • Crossing-over is when chromosomes overlap and exchange portions of their chromatids.
prophase i1
Prophase I

http://videos.howstuffworks.com/hsw/5987-mitosis-and-meiosis-prophase-one-video.htm

metaphase i
Metaphase I
  • Spindle fibers attach to the chromosomes
metaphase i1
Metaphase I

http://videos.howstuffworks.com/hsw/5988-mitosis-and-meiosis-metaphase-one-video.htm

anaphase i
Anaphase I
  • The fibers pull the homologous chromosomes toward opposite ends of the cell.
  • Notice that in anaphase I the sister chromatids remain attached at their centromeres and move together toward the poles.
  • A key difference between mitosis and meiosis is that sister chromatids remain joined after metaphase in meiosis I, whereas in mitosis they separate.
anaphase i1
Anaphase I

http://videos.howstuffworks.com/hsw/5989-mitosis-and-meiosis-anaphase-one-video.htm

telophase i
Telophase I
  • A nuclear envelope reforms around each chromosome set, the spindle disappers, and cytokinesis follows.
telophase 1
Telophase 1

http://videos.howstuffworks.com/hsw/5990-mitosis-and-meiosis-telophase-one-video.htm

cytokinesis
Cytokinesis
  • Cytokinesis is not one of the stages or phases of meiosis or mitosis. It is the process of division that the cytoplasm undergoes when it is distributed into daughter cells
  • In animal cells, cytokinesis involves the formation of a cleavage furrow, resulting in the pinching of the cell into two cells.
  • After cytokinesis, each of the two progeny cells has a nucleus with a haploid set of replicated chromosomes.
prophase ii
Prophase II
  • Meiosis I results in two haploid (N) cells.
  • Each cell has half the number of chromosomes as the original cell.
  • There is no DNA replication between the two cell divisions.
  • The nuclear envelope breaks down, and the spindle apparatus forms.
prophase ii1
Prophase II

http://videos.howstuffworks.com/hsw/5991-mitosis-and-meiosis-prophase-two-video.htm

metaphase ii
Metaphase II
  • The chromosomes line up similar to metaphase in mitosis.
metaphase ii1
Metaphase II

http://videos.howstuffworks.com/hsw/5992-mitosis-and-meiosis-metaphase-two-video.htm

anaphase ii
Anaphase II
  • Sister chromatids separate and move to opposite ends of the cell.
anaphase ii1
Anaphase II

http://videos.howstuffworks.com/hsw/5993-mitosis-and-meiosis-anaphase-two-video.htm

telophase ii
Telophase II
  • Meiosis II results in 4 haploid cells (gametes in animals)
  • Because of crossing-over, some chromosomes are seen to have recombined segments of the original parental chromosomes.
telophase ii1
Telophase II

http://videos.howstuffworks.com/hsw/5994-mitosis-and-meiosis-telophase-two-video.htm

gamete formation
Gamete Formation
  • In males, meiosis results in 4 sperm cells
  • In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction.
stages of meiosis
Stages of Meiosis

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of%20Meiosis

how cells divide mitosis vs meiosis
How Cells Divide: Mitosis vs Meiosis

http://www.teachersdomain.org/resource/tdc02.sci.life.gen.mitosis/

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