{"id":2410,"date":"2016-05-24T20:57:56","date_gmt":"2016-05-24T20:57:56","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/biologyxwaymakerxmaster\/?post_type=chapter&#038;p=2410"},"modified":"2024-04-26T22:30:27","modified_gmt":"2024-04-26T22:30:27","slug":"reading-meiosis-ii","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology1\/chapter\/reading-meiosis-ii\/","title":{"raw":"Meiosis II","rendered":"Meiosis II"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Describe the steps of meiosis II<\/li>\r\n<\/ul>\r\n<\/div>\r\nIn some species, cells enter a brief interphase, or\u00a0<strong>interkinesis<\/strong>, before entering meiosis II. Interkinesis lacks an S phase, so chromosomes are not duplicated. The two cells produced in meiosis I go through the events of meiosis II in synchrony. During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes. The mechanics of meiosis II is similar to mitosis, except that each dividing cell has only one set of homologous chromosomes. Therefore, each cell has half the number of sister chromatids to separate out as a diploid cell undergoing mitosis.\r\n<h2>Prophase II<\/h2>\r\nIf the chromosomes decondensed in telophase I, they condense again. If nuclear envelopes were formed, they fragment into vesicles. The centrosomes that were duplicated during interkinesis move away from each other toward opposite poles, and new spindles are formed.\r\n<h2>Prometaphase II<\/h2>\r\nThe nuclear envelopes are completely broken down, and the spindle is fully formed. Each sister chromatid forms an individual kinetochore that attaches to microtubules from opposite poles.\r\n<h2>Metaphase II<\/h2>\r\nThe sister chromatids are maximally condensed and aligned at the equator of the cell.\r\n<h2>Anaphase II<\/h2>\r\nThe sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles. Non-kinetochore microtubules elongate the cell.\r\n\r\n[caption id=\"attachment_1818\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-1818\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/03212035\/Figure_11_01_041-1024x822.jpg\" alt=\"This illustration compares chromosome alignment in meiosis I and meiosis II. In prometaphase I, homologous pairs of chromosomes are held together by chiasmata. In anaphase I, the homologous pair separates and the connections at the chiasmata are broken, but the sister chromatids remain attached at the centromere. In prometaphase II, the sister chromatids are held together at the centromere. In anaphase II, the centromere connections are broken and the sister chromatids separate.\" width=\"1024\" height=\"822\" \/> Figure 1. The process of chromosome alignment differs between meiosis I and meiosis II. In prometaphase I, microtubules attach to the fused kinetochores of homologous chromosomes, and the homologous chromosomes are arranged at the midpoint of the cell in metaphase I. In anaphase I, the homologous chromosomes are separated. In prometaphase II, microtubules attach to the kinetochores of sister chromatids, and the sister chromatids are arranged at the midpoint of the cells in metaphase II. In anaphase II, the sister chromatids are separated.[\/caption]\r\n<h2>Telophase II and Cytokinesis<\/h2>\r\nThe chromosomes arrive at opposite poles and begin to decondense. Nuclear envelopes form around the chromosomes. Cytokinesis separates the two cells into four unique haploid cells. At this point, the newly formed nuclei are both haploid. The cells produced are genetically unique because of the random assortment of paternal and maternal homologs and because of the recombining of maternal and paternal segments of chromosomes (with their sets of genes) that occurs during crossover. The entire process of meiosis is outlined in Figure 2.\r\n\r\n[caption id=\"attachment_1819\" align=\"aligncenter\" width=\"730\"]<img class=\"size-large wp-image-1819\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/03212218\/Figure_11_01_051-730x1024.jpg\" alt=\"This illustration outlines the stages of meiosis. In interphase, before meiosis begins, the chromosomes are duplicated. Meiosis I then proceeds through several stages. In prophase I, the chromosomes begin to condense and the nuclear envelope fragments. Homologous pairs of chromosomes line up, and chiasmata form between them. Crossing over occurs at the chiasmata. Spindle fibers emerge from the centrosomes. In prometaphase I, homologous chromosomes attach to the spindle microtubules. In metaphase I, homologous chromosomes line up at the metaphase plate. In anaphase I, the spindle microtubules pull the homologous pairs of chromosomes apart. In telophase I and cytokinesis, the sister chromatids arrive at the poles of the cell and begin to decondense. The nuclear envelope begins to form again, and cell division occurs. Meiosis II then proceeds through several stages. In prophase II, the sister chromatids condense and the nuclear envelope fragments. A new spindle begins to form. In prometaphase II, the sister chromatids become attached to the kinetochore. In metaphase II, the sister chromatids line up at the metaphase plate. In anaphase II, the sister chromatids are pulled apart by the shortening spindles. In telophase II and cytokinesis, the nuclear envelope forms again and cell division occurs, resulting in four haploid daughter cells.\" width=\"730\" height=\"1024\" \/> Figure 2. An animal cell with a diploid number of four (2<em>n<\/em> = 4) proceeds through the stages of meiosis to form four haploid daughter cells.[\/caption]\r\n\r\n<div class=\"textbox shaded\">Review the process of meiosis, observing how chromosomes align and migrate, at\u00a0<a href=\"http:\/\/www.cellsalive.com\/meiosis_js.htm\" target=\"_blank\" rel=\"noopener\">Meiosis: An Interactive Animation<\/a>.<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/5cd02872-8b8b-4a04-8b8f-4bc5478fb4a0\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Describe the steps of meiosis II<\/li>\n<\/ul>\n<\/div>\n<p>In some species, cells enter a brief interphase, or\u00a0<strong>interkinesis<\/strong>, before entering meiosis II. Interkinesis lacks an S phase, so chromosomes are not duplicated. The two cells produced in meiosis I go through the events of meiosis II in synchrony. During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes. The mechanics of meiosis II is similar to mitosis, except that each dividing cell has only one set of homologous chromosomes. Therefore, each cell has half the number of sister chromatids to separate out as a diploid cell undergoing mitosis.<\/p>\n<h2>Prophase II<\/h2>\n<p>If the chromosomes decondensed in telophase I, they condense again. If nuclear envelopes were formed, they fragment into vesicles. The centrosomes that were duplicated during interkinesis move away from each other toward opposite poles, and new spindles are formed.<\/p>\n<h2>Prometaphase II<\/h2>\n<p>The nuclear envelopes are completely broken down, and the spindle is fully formed. Each sister chromatid forms an individual kinetochore that attaches to microtubules from opposite poles.<\/p>\n<h2>Metaphase II<\/h2>\n<p>The sister chromatids are maximally condensed and aligned at the equator of the cell.<\/p>\n<h2>Anaphase II<\/h2>\n<p>The sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles. Non-kinetochore microtubules elongate the cell.<\/p>\n<div id=\"attachment_1818\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1818\" class=\"size-large wp-image-1818\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/03212035\/Figure_11_01_041-1024x822.jpg\" alt=\"This illustration compares chromosome alignment in meiosis I and meiosis II. In prometaphase I, homologous pairs of chromosomes are held together by chiasmata. In anaphase I, the homologous pair separates and the connections at the chiasmata are broken, but the sister chromatids remain attached at the centromere. In prometaphase II, the sister chromatids are held together at the centromere. In anaphase II, the centromere connections are broken and the sister chromatids separate.\" width=\"1024\" height=\"822\" \/><\/p>\n<p id=\"caption-attachment-1818\" class=\"wp-caption-text\">Figure 1. The process of chromosome alignment differs between meiosis I and meiosis II. In prometaphase I, microtubules attach to the fused kinetochores of homologous chromosomes, and the homologous chromosomes are arranged at the midpoint of the cell in metaphase I. In anaphase I, the homologous chromosomes are separated. In prometaphase II, microtubules attach to the kinetochores of sister chromatids, and the sister chromatids are arranged at the midpoint of the cells in metaphase II. In anaphase II, the sister chromatids are separated.<\/p>\n<\/div>\n<h2>Telophase II and Cytokinesis<\/h2>\n<p>The chromosomes arrive at opposite poles and begin to decondense. Nuclear envelopes form around the chromosomes. Cytokinesis separates the two cells into four unique haploid cells. At this point, the newly formed nuclei are both haploid. The cells produced are genetically unique because of the random assortment of paternal and maternal homologs and because of the recombining of maternal and paternal segments of chromosomes (with their sets of genes) that occurs during crossover. The entire process of meiosis is outlined in Figure 2.<\/p>\n<div id=\"attachment_1819\" style=\"width: 740px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1819\" class=\"size-large wp-image-1819\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/03212218\/Figure_11_01_051-730x1024.jpg\" alt=\"This illustration outlines the stages of meiosis. In interphase, before meiosis begins, the chromosomes are duplicated. Meiosis I then proceeds through several stages. In prophase I, the chromosomes begin to condense and the nuclear envelope fragments. Homologous pairs of chromosomes line up, and chiasmata form between them. Crossing over occurs at the chiasmata. Spindle fibers emerge from the centrosomes. In prometaphase I, homologous chromosomes attach to the spindle microtubules. In metaphase I, homologous chromosomes line up at the metaphase plate. In anaphase I, the spindle microtubules pull the homologous pairs of chromosomes apart. In telophase I and cytokinesis, the sister chromatids arrive at the poles of the cell and begin to decondense. The nuclear envelope begins to form again, and cell division occurs. Meiosis II then proceeds through several stages. In prophase II, the sister chromatids condense and the nuclear envelope fragments. A new spindle begins to form. In prometaphase II, the sister chromatids become attached to the kinetochore. In metaphase II, the sister chromatids line up at the metaphase plate. In anaphase II, the sister chromatids are pulled apart by the shortening spindles. In telophase II and cytokinesis, the nuclear envelope forms again and cell division occurs, resulting in four haploid daughter cells.\" width=\"730\" height=\"1024\" \/><\/p>\n<p id=\"caption-attachment-1819\" class=\"wp-caption-text\">Figure 2. An animal cell with a diploid number of four (2<em>n<\/em> = 4) proceeds through the stages of meiosis to form four haploid daughter cells.<\/p>\n<\/div>\n<div class=\"textbox shaded\">Review the process of meiosis, observing how chromosomes align and migrate, at\u00a0<a href=\"http:\/\/www.cellsalive.com\/meiosis_js.htm\" target=\"_blank\" rel=\"noopener\">Meiosis: An Interactive Animation<\/a>.<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_5cd02872-8b8b-4a04-8b8f-4bc5478fb4a0\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/5cd02872-8b8b-4a04-8b8f-4bc5478fb4a0?iframe_resize_id=assessment_practice_id_5cd02872-8b8b-4a04-8b8f-4bc5478fb4a0\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-2410\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":16,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"1e12f27c-8464-4b8a-bd88-e0e5ee17c8fe, 1fa30008-bb9b-4c14-92ac-823de67d548a","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2410","chapter","type-chapter","status-publish","hentry"],"part":205,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2410","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":8,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2410\/revisions"}],"predecessor-version":[{"id":5950,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2410\/revisions\/5950"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/parts\/205"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2410\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/media?parent=2410"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapter-type?post=2410"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/contributor?post=2410"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/license?post=2410"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}