Meiosis

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=90 BGCOLOR="#006699" TEXT="#080000" bgproperties="fixed" background="02c285a1erlcgo.png"> <div> <FONT SIZE="5" COLOR="#FFCC66" FACE="Arial" ><B>Mr. Manning's Life Science Class</B></FONT><B>     |     </B><A HREF="index.htm" TARGET="_top" TITLE="Mr. Mannings Life Science Class"><B>home</B></A></div> <div> <B>Meiosis</B>   |   <A HREF="id206.htm" TARGET="_top" TITLE="Meiosis I">Meiosis I</A>   |   <A HREF="id208.htm" TARGET="_top" TITLE="Concept 6: Meiosis I: Anaphase I">Concept 6: Meiosis I: Anaphase I</A>   |   <A HREF="id207.htm" TARGET="_top" TITLE="Concept 5: Meiosis I Metaphase I">Concept 5: Meiosis I Metaphase I</A>   |   <A HREF="id210.htm" TARGET="_top" TITLE="Concept 8: Meiosis I Animated">Concept 8: Meiosis I Animated</A>   |   <A HREF="id209.htm" TARGET="_top" TITLE="Concept 7: Meiosis I: Telophase I">Concept 7: Meiosis I: Telophase I</A>   |   <A HREF="id211.htm" TARGET="_top" TITLE="Concept 10: Meiosis II Prophase II">Concept 10: Meiosis II Prophase II</A>   |   <A HREF="id212.htm" TARGET="_top" TITLE="Meiosis II Metaphase II">Meiosis II Metaphase II</A>   |   <A HREF="id213.htm" TARGET="_top" TITLE="Concept 12: Meiosis II: Anaphase II">Concept 12: Meiosis II: Anaphase II</A>   |   <A HREF="id214.htm" TARGET="_top" TITLE="Concept 13: Meiosis II: Telophase II">Concept 13: Meiosis II: Telophase II</A>   |   <A HREF="id215.htm" TARGET="_top" TITLE="Concept 14: Meiosis II Animated">Concept 14: Meiosis II Animated</A>   |   <A HREF="id216.htm" TARGET="_top" TITLE="Concept 16: Gene Segregation in Meiosis ">Concept 16: Gene Segregation in Meiosis - 1</A>   |   <A HREF="id217.htm" TARGET="_top" TITLE="Concept 17: Gene Segregation in Meiosis ">Concept 17: Gene Segregation in Meiosis - 2</A></div> <div> </div> </td> </tr><tr> <td valign="top" width=210 BGCOLOR="#FFCC66" TEXT="#080000" background="02ad2c00dkelyh.png"> <div> <A HREF="id205_m.htm#meiosis_" TARGET="TRLX_Middle" TITLE="Meiosis">Meiosis </A></div> <div> <A HREF="id205_m.htm#concept_1_an_overview" TARGET="TRLX_Middle" TITLE="Meiosis">Concept 1 An Overview</A></div> <div> <A HREF="id205_m.htm#concept_2_the_process_of_meiosis" TARGET="TRLX_Middle" TITLE="Meiosis">Concept 2 The Process of Meiosis</A></div> <div> <A HREF="id205_m.htm#concept_3_premeiotic_interphase" TARGET="TRLX_Middle" TITLE="Meiosis">Concept 3 Premeiotic Interphase</A></div> <bR> <div> Continue on to next section </div> <div> click on</div> <div> <A HREF="id206_concept_4_meiosis_i_prophase_i.htm" TARGET="_top" TITLE="Meiosis I">Concept 4 Meiosis I Prophase I</A></div> <div> ____________________________</div> <div> To go to the second part of Meiosis click</div> <div> <A HREF="id211_concept_10_meiosis_ii_prophase_ii.htm" TARGET="_top" TITLE="Concept 10: Meiosis II Prophase II">Concept 10 Meiosis II Prophase II</A></div> <bR> <bR> <bR> </td> <td valign="top" height=390 width="100%" BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <I>Meiosis</I></div> <div>  <A NAME="meiosis_"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><B><U>Meiosis </U></B></div> <bR> <div> <B> <A NAME="introduction"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B><B>Introduction</B> </div> <div> This activity will help you review <U>meiosis</U>, <U>the two successive divisions of a diploid cell of a sexually reproducing organism</U> that <U>result </U>in <U>four haploid progeny cells</U>, each <U>with half the genetic material of the original cell</U>.</div> <bR> <div> You will find information about the process of meiosis, and the relevance of meiosis to genetics. Animations show the process of meiosis in a dynamic way.</div> <bR> <div> You can <U>test your understanding</U> of meiosis by <U>using the Self-Quiz</U> at the end of the module. </div> <bR> <div> For comparison purposes, mitosis is the process of cell division in eukaryotes, in which the parental chromosome number is conserved in each of the daughter cells, while <U>meiosis is a two-cell-division process in sexually reproducing eukaryotes</U> that <U>results </U>in <U>cells (typically gametes) with one-half the chromosome number of the original parental cell</U>.</div> <bR> <div> <B> <A NAME="concept_1_an_overview"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B><A HREF="#concept_1_an_overview" TITLE="Meiosis"><B>Concept 1: An Overview</B></A><A HREF="#concept_1_an_overview" TITLE="Meiosis"> </A></div> <div> Meiosis involves two successive divisions of a diploid (2N) eukaryotic cell of a sexually reproducing organism that result in four haploid (N) progeny cells, each with half of the genetic material of the original cell. Through the mechanisms by which paternal and maternal chromosomes segregate, and the process of crossing-over, genetic variation is produced in the haploid cells.</div> <bR> <div> <IMG SRC="7da67230.gif" border=0 width="359" height="291" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Meiosis occurs in diploid cells. The chromosomes duplicate once, and through two successive divisions, four haploid cells are produced, each with half the chromosome number of the parental cell.</div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Meiosis occurs only in sexually reproducing organisms. Depending on the organism, it may produce haploid gametes, which do not divide further but instead fuse to produce a diploid zygote; or it may produce haploid spores, which divide by mitotic cell cycles and produce unicellular or multicellular organisms.</div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">In animals, where the somatic (body) cells are diploid, the products of meiosis are the gametes.</div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">In many fungi and some algae, meiosis occurs immediately after two haploid cells fuse, and mitosis then produces a haploid multicellular "adult" organism (e.g., filamentous fungi, algae) or haploid unicellular organisms (e.g., yeast, unicellular algae).</div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Plants and some algae have both haploid and diploid multicellular stages. The multicellular diploid stage is the sporophyte. Meiosis in a sporophyte produces haploid spores. These spores alone are capable of generating a haploid multicellular stage called a gametophyte. The gametophyte produces gametes by mitotic cell cycles.</div> <bR> <bR> <div> <B> <A NAME="concept_2_the_process_of_meiosis"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B><B>Concept 2: The Process of Meiosis</B> </div> <div> Meiosis consists of two successive nuclear divisions, meiosis I and meiosis II. Each division consists of these stages: prophase, metaphase, anaphase, and telophase. </div> <bR> <div> We will follow meiosis in an animal cell with two pairs of chromosomes.</div> <bR> <div> <B> <A NAME="concept_3_premeiotic_interphase"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B><B>Concept 3: Premeiotic Interphase </B></div> <div> The chromosomes duplicate prior to meiosis.</div> <bR> <div> <IMG SRC="7db909a0.gif" border=0 width="400" height="154" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Prior to meiosis, all chromosomes are duplicated in a process similar to chromosome duplication prior to mitosis.</div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Outside the nucleus of animal cells are two centrosomes, each containing a pair of centrioles. The two centrosomes are produced by the duplication of a single centrosome during premeiotic interphase. The centrosomes serve as microtubule organizing centers (MTOCs). Microtubules extend radially from centrosomes, forming an aster.</div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Plant cells do not have centrosomes. Different kinds of microtubule organizing centers serve as sites of spindle formation.</div> <bR> <bR> <div> <FONT SIZE="3" COLOR="#000000" FACE="Comic Sans MS" >Click </FONT><B> </B><A HREF="id206_meiosis_i.htm" TARGET="_top" TITLE="Meiosis I"><B>Meiosis I</B></A><FONT SIZE="3" COLOR="#000000" FACE="Comic Sans MS" > to continue.</FONT></div> <bR> <div> Click <FONT SIZE="3" COLOR="#000099" FACE="Comic Sans MS" >Meiosis II Prophase II</FONT> to go to the second part of meiosis.       </div> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> </td> </tr></table></body>