{"id":940,"date":"2015-10-28T15:56:53","date_gmt":"2015-10-28T19:56:53","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/chapter\/24-7-organogenesis-and-vertebrate-formation\/"},"modified":"2021-02-26T17:51:11","modified_gmt":"2021-02-26T22:51:11","slug":"24-7-organogenesis-and-vertebrate-formation","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/chapter\/24-7-organogenesis-and-vertebrate-formation\/","title":{"raw":"24.7.\u00a0Organogenesis and Vertebrate Formation","rendered":"24.7.\u00a0Organogenesis and Vertebrate Formation"},"content":{"raw":"<div class=\"section module\" title=\"43.7.\u00a0Organogenesis and Vertebrate Formation\" xml:lang=\"en\">\r\n<div class=\"titlepage\">\r\n<div class=\"abstract\">\r\n<div class=\"bcc-box bcc-highlight\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to:\r\n<div class=\"itemizedlist\">\r\n<ul class=\"itemizedlist\">\r\n \t<li class=\"listitem\">Describe the process of organogenesis<\/li>\r\n \t<li class=\"listitem\">Identify the anatomical axes formed in vertebrates<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span id=\"m44850-fs-idp61264496\"> <\/span>Gastrulation leads to the formation of the three germ layers that give rise, during further development, to the different organs in the animal body. This process is called <strong>organogenesis<\/strong><a id=\"id861547\" class=\"indexterm\"><\/a>. Organogenesis is characterized by rapid and precise movements of the cells within the embryo.\r\n<div class=\"section\" title=\"Organogenesis\">\r\n<div class=\"titlepage\">\r\n<div>\r\n<div>\r\n<h2 id=\"m44850-fs-idp168808848\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Organogenesis<\/span><\/span><\/h2>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span id=\"m44850-fs-idp65996928\"> <\/span>Organs form from the germ layers through the process of differentiation. During differentiation, the embryonic stem cells express specific sets of genes which will determine their ultimate cell type. For example, some cells in the ectoderm will express the genes specific to skin cells. As a result, these cells will differentiate into epidermal cells. The process of differentiation is regulated by cellular signaling cascades.\r\n\r\n<span id=\"m44850-fs-idm16832384\"> <\/span>Scientists study organogenesis extensively in the lab in fruit flies (<span class=\"emphasis\"><em>Drosophila<\/em><\/span>) and the nematode <span class=\"emphasis\"><em>Caenorhabditis elegans<\/em><\/span>. <span class=\"emphasis\"><em>Drosophila<\/em><\/span> have segments along their bodies, and the patterning associated with the segment formation has allowed scientists to study which genes play important roles in organogenesis along the length of the embryo at different time points. The nematode <span class=\"emphasis\"><em>C.elegans<\/em><\/span> has roughly 1000 somatic cells and scientists have studied the fate of each of these cells during their development in the nematode life cycle. There is little variation in patterns of cell lineage between individuals, unlike in mammals where cell development from the embryo is dependent on cellular cues.\r\n\r\n<span id=\"m44850-fs-idp65133440\"> <\/span>In vertebrates, one of the primary steps during organogenesis is the formation of the neural system. The ectoderm forms epithelial cells and tissues, and neuronal tissues. During the formation of the neural system, special signaling molecules called growth factors signal some cells at the edge of the ectoderm to become epidermis cells. The remaining cells in the center form the neural plate. If the signaling by growth factors were disrupted, then the entire ectoderm would differentiate into neural tissue.\r\n\r\n<span id=\"m44850-fs-idm17573616\"> <\/span>The neural plate undergoes a series of cell movements where it rolls up and forms a tube called the <span id=\"m44850-autoid-cnx2dbk-id1737007\"> <\/span><strong>neural tube<\/strong>, as illustrated in\r\n\r\n<\/div>\r\n<a class=\"xref target-figure\" title=\"Figure\u00a043.28.\u00a0\" href=\"#attachment_1418\">Figure 24.28<\/a>. In further development, the neural tube will give rise to the brain and the spinal cord.\r\n\r\n[caption id=\"attachment_1418\" align=\"aligncenter\" width=\"350\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_43_06_01.jpg\"><img class=\"wp-image-937\" src=\"https:\/\/pressbooks.bccampus.ca\/knowinghome\/wp-content\/uploads\/sites\/1064\/2015\/10\/Figure_43_06_01.jpg\" alt=\"Figure_43_06_01\" width=\"350\" height=\"522\" \/><\/a> Figure 24.28.\u00a0 The central region of the ectoderm forms the neural tube, which gives rise to the brain and the spinal cord.[\/caption]\r\n\r\n<span id=\"m44850-fs-idp7077728\"> <\/span>The mesoderm that lies on either side of the vertebrate neural tube will develop into the various connective tissues of the animal body. A spatial pattern of gene expression reorganizes the mesoderm into groups of cells called <span id=\"m44850-autoid-cnx2dbk-id1717348\"> <\/span><strong>somites<\/strong> with spaces between them. The somites, illustrated in <a class=\"xref target-figure\" title=\"Figure\u00a043.29.\u00a0\" href=\"#attachment_1419\">Figure 24.29<\/a> will further develop into the ribs, lungs, and segmental (spine) muscle. The mesoderm also forms a structure called the notochord, which is rod-shaped and forms the central axis of the animal body.\r\n\r\n[caption id=\"attachment_1419\" align=\"aligncenter\" width=\"350\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_43_06_02.jpg\"><img class=\"wp-image-938\" src=\"https:\/\/pressbooks.bccampus.ca\/knowinghome\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_02.jpg\" alt=\"Figure_43_06_02\" width=\"350\" height=\"373\" \/><\/a> Figure 24.29.\u00a0 In this five-week old human embryo, somites are segments along the length of the body. (credit: modification of work by Ed Uthman)[\/caption]\r\n\r\n<\/div>\r\n<div class=\"section\" title=\"Vertebrate Axis Formation\">\r\n<div class=\"titlepage\">\r\n<div>\r\n<div>\r\n<h2 id=\"m44850-fs-idm60055584\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Vertebrate Axis Formation<\/span><\/span><\/h2>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span id=\"m44850-fs-idm60224592\"> <\/span>Even as the germ layers form, the ball of cells still retains its spherical shape. However, animal bodies have lateral-medial (left-right), dorsal-ventral (back-belly), and anterior-posterior (head-feet) axes, illustrated in <a class=\"xref target-figure\" title=\"Figure\u00a043.30.\u00a0\" href=\"#attachment_1420\">Figure 24.30<\/a>.\r\n\r\n[caption id=\"attachment_1420\" align=\"aligncenter\" width=\"600\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_43_06_03.jpg\"><img class=\"wp-image-1420\" src=\"https:\/\/pressbooks.bccampus.ca\/knowinghome\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_03-1024x475-1.jpg\" alt=\"Figure_43_06_03\" width=\"600\" height=\"278\" \/><\/a> Figure 24.30.\u00a0 Animal bodies have three axes for symmetry. (credit: modification of work by NOAA)[\/caption]\r\n\r\n<span id=\"m44850-fs-idp23643616\"> <\/span>How are these established? In one of the most seminal experiments ever to be carried out in developmental biology, Spemann and Mangold took dorsal cells from one embryo and transplanted them into the belly region of another embryo. They found that the transplanted embryo now had two notochords: one at the dorsal site from the original cells and another at the transplanted site. This suggested that the dorsal cells were genetically programmed to form the notochord and define the axis. Since then, researchers have identified many genes that are responsible for axis formation. Mutations in these genes leads to the loss of symmetry required for organism development.\r\n\r\n<span id=\"m44850-fs-idp164017568\"> <\/span>Animal bodies have externally visible symmetry. However, the internal organs are not symmetric. For example, the heart is on the left side and the liver on the right. The formation of the central left-right axis is an important process during development. This internal asymmetry is established very early during development and involves many genes. Research is still ongoing to fully understand the developmental implications of these genes.\r\n<h2>Summary<\/h2>\r\nOrganogenesis is the formation of organs from the germ layers. Each germ layer gives rise to specific tissue types. The first stage is the formation of the neural system in the ectoderm. The mesoderm gives rise to somites and the notochord. Formation of vertebrate axis is another important developmental stage.\r\n<div class=\"title\">\r\n<div class=\"title\">\r\n<div class=\"bcc-box bcc-info\">\r\n<h3>Exercises<\/h3>\r\n<div class=\"section\">\r\n<div class=\"body\">\r\n<div id=\"m44850-fs-idm29405328\" class=\"exercise\">\r\n<div class=\"body\">\r\n<div class=\"problem\">\r\n<ol>\r\n \t<li>Which of the following gives rise to the skin cells?\r\n<ol>\r\n \t<li>ectoderm<\/li>\r\n \t<li>endoderm<\/li>\r\n \t<li>mesoderm<\/li>\r\n \t<li>none of the above<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>The ribs form from the ________.\r\n<ol>\r\n \t<li>notochord<\/li>\r\n \t<li>neural plate<\/li>\r\n \t<li>neural tube<\/li>\r\n \t<li>somites<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>Explain how the different germ layers give rise to different tissue types.<\/li>\r\n \t<li>Explain the role of axis formation in development<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"cnx-eoc free-response\">\r\n<div id=\"m44850-fs-idp121762688\" class=\"exercise\">\r\n<div class=\"body\">\r\n<div id=\"m44850-fs-idp20676832\" class=\"solution labeled\">\r\n<div class=\"body\">\r\n\r\n<strong>Answers<\/strong>\r\n<ol>\r\n \t<li>A<\/li>\r\n \t<li>D<\/li>\r\n \t<li>Organs form from the germ layers through the process of differentiation. During differentiation, the embryonic stem cells express a specific set of genes that will determine their ultimate fate as a cell type. For example, some cells in the ectoderm will express the genes specific to skin cells. As a result, these cells will differentiate into epidermal cells. The process of differentiation is regulated by cellular signaling cascades.<\/li>\r\n \t<li>Animal bodies have lateral-medial (left-right), dorsal-ventral (back-belly), and anterior-posterior (head-feet) axes. The dorsal cells are genetically programmed to form the notochord and define the axis. There are many genes responsible for axis formation. Mutations in these genes lead to the loss of symmetry required for organism development.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"id862105\" class=\"glossary\" title=\"Glossary\">\r\n<div class=\"titlepage\">\r\n<div class=\"bcc-box bcc-success\">\r\n<h3>Glossary<\/h3>\r\n<dl>\r\n \t<dt><strong>morning sickness<\/strong><\/dt>\r\n \t<dd>condition in the mother during the first trimester; includes feelings of nausea<\/dd>\r\n \t<dt><strong>neural tube<\/strong><\/dt>\r\n \t<dd>tube-like structure that forms from the ectoderm and gives rise to the brain and spinal cord<\/dd>\r\n \t<dt><strong>oogenesis<\/strong><\/dt>\r\n \t<dd>process of producing haploid eggs<\/dd>\r\n \t<dt><strong>organogenesis<\/strong><\/dt>\r\n \t<dd>process of organ formation<\/dd>\r\n \t<dt><strong>oviduct<\/strong><\/dt>\r\n \t<dd>(also, fallopian tube) muscular tube connecting the uterus with the ovary area<\/dd>\r\n \t<dt><strong>somite<\/strong><\/dt>\r\n \t<dd>group of cells separated by small spaces that form from the mesoderm and give rise to connective tissue<\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"cnx-eoc summary\">\r\n<div class=\"cnx-eoc art-exercise\">\r\n<div class=\"section empty\">\r\n<div class=\"section empty\">\r\n<div class=\"section empty\">\r\n<div class=\"section\">\r\n<div class=\"body\">\r\n<div id=\"m44839-fs-idp69205744\" class=\"exercise\"><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"<div class=\"section module\" title=\"43.7.\u00a0Organogenesis and Vertebrate Formation\" xml:lang=\"en\">\n<div class=\"titlepage\">\n<div class=\"abstract\">\n<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<div class=\"itemizedlist\">\n<ul class=\"itemizedlist\">\n<li class=\"listitem\">Describe the process of organogenesis<\/li>\n<li class=\"listitem\">Identify the anatomical axes formed in vertebrates<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44850-fs-idp61264496\"> <\/span>Gastrulation leads to the formation of the three germ layers that give rise, during further development, to the different organs in the animal body. This process is called <strong>organogenesis<\/strong><a id=\"id861547\" class=\"indexterm\"><\/a>. Organogenesis is characterized by rapid and precise movements of the cells within the embryo.<\/p>\n<div class=\"section\" title=\"Organogenesis\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44850-fs-idp168808848\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Organogenesis<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44850-fs-idp65996928\"> <\/span>Organs form from the germ layers through the process of differentiation. During differentiation, the embryonic stem cells express specific sets of genes which will determine their ultimate cell type. For example, some cells in the ectoderm will express the genes specific to skin cells. As a result, these cells will differentiate into epidermal cells. The process of differentiation is regulated by cellular signaling cascades.<\/p>\n<p><span id=\"m44850-fs-idm16832384\"> <\/span>Scientists study organogenesis extensively in the lab in fruit flies (<span class=\"emphasis\"><em>Drosophila<\/em><\/span>) and the nematode <span class=\"emphasis\"><em>Caenorhabditis elegans<\/em><\/span>. <span class=\"emphasis\"><em>Drosophila<\/em><\/span> have segments along their bodies, and the patterning associated with the segment formation has allowed scientists to study which genes play important roles in organogenesis along the length of the embryo at different time points. The nematode <span class=\"emphasis\"><em>C.elegans<\/em><\/span> has roughly 1000 somatic cells and scientists have studied the fate of each of these cells during their development in the nematode life cycle. There is little variation in patterns of cell lineage between individuals, unlike in mammals where cell development from the embryo is dependent on cellular cues.<\/p>\n<p><span id=\"m44850-fs-idp65133440\"> <\/span>In vertebrates, one of the primary steps during organogenesis is the formation of the neural system. The ectoderm forms epithelial cells and tissues, and neuronal tissues. During the formation of the neural system, special signaling molecules called growth factors signal some cells at the edge of the ectoderm to become epidermis cells. The remaining cells in the center form the neural plate. If the signaling by growth factors were disrupted, then the entire ectoderm would differentiate into neural tissue.<\/p>\n<p><span id=\"m44850-fs-idm17573616\"> <\/span>The neural plate undergoes a series of cell movements where it rolls up and forms a tube called the <span id=\"m44850-autoid-cnx2dbk-id1737007\"> <\/span><strong>neural tube<\/strong>, as illustrated in<\/p>\n<\/div>\n<p><a class=\"xref target-figure\" title=\"Figure\u00a043.28.\u00a0\" href=\"#attachment_1418\">Figure 24.28<\/a>. In further development, the neural tube will give rise to the brain and the spinal cord.<\/p>\n<figure id=\"attachment_1418\" aria-describedby=\"caption-attachment-1418\" style=\"width: 350px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_43_06_01.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-937\" src=\"https:\/\/pressbooks.bccampus.ca\/knowinghome\/wp-content\/uploads\/sites\/1064\/2015\/10\/Figure_43_06_01.jpg\" alt=\"Figure_43_06_01\" width=\"350\" height=\"522\" srcset=\"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2015\/10\/Figure_43_06_01.jpg 544w, https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2015\/10\/Figure_43_06_01-201x300.jpg 201w, https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2015\/10\/Figure_43_06_01-65x97.jpg 65w, https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2015\/10\/Figure_43_06_01-225x336.jpg 225w, https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2015\/10\/Figure_43_06_01-350x522.jpg 350w\" sizes=\"auto, (max-width: 350px) 100vw, 350px\" \/><\/a><figcaption id=\"caption-attachment-1418\" class=\"wp-caption-text\">Figure 24.28.\u00a0 The central region of the ectoderm forms the neural tube, which gives rise to the brain and the spinal cord.<\/figcaption><\/figure>\n<p><span id=\"m44850-fs-idp7077728\"> <\/span>The mesoderm that lies on either side of the vertebrate neural tube will develop into the various connective tissues of the animal body. A spatial pattern of gene expression reorganizes the mesoderm into groups of cells called <span id=\"m44850-autoid-cnx2dbk-id1717348\"> <\/span><strong>somites<\/strong> with spaces between them. The somites, illustrated in <a class=\"xref target-figure\" title=\"Figure\u00a043.29.\u00a0\" href=\"#attachment_1419\">Figure 24.29<\/a> will further develop into the ribs, lungs, and segmental (spine) muscle. The mesoderm also forms a structure called the notochord, which is rod-shaped and forms the central axis of the animal body.<\/p>\n<figure id=\"attachment_1419\" aria-describedby=\"caption-attachment-1419\" style=\"width: 350px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_43_06_02.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-938\" src=\"https:\/\/pressbooks.bccampus.ca\/knowinghome\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_02.jpg\" alt=\"Figure_43_06_02\" width=\"350\" height=\"373\" srcset=\"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_02.jpg 544w, https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_02-281x300.jpg 281w, https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_02-65x69.jpg 65w, https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_02-225x240.jpg 225w, https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_02-350x373.jpg 350w\" sizes=\"auto, (max-width: 350px) 100vw, 350px\" \/><\/a><figcaption id=\"caption-attachment-1419\" class=\"wp-caption-text\">Figure 24.29.\u00a0 In this five-week old human embryo, somites are segments along the length of the body. (credit: modification of work by Ed Uthman)<\/figcaption><\/figure>\n<\/div>\n<div class=\"section\" title=\"Vertebrate Axis Formation\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44850-fs-idm60055584\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Vertebrate Axis Formation<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44850-fs-idm60224592\"> <\/span>Even as the germ layers form, the ball of cells still retains its spherical shape. However, animal bodies have lateral-medial (left-right), dorsal-ventral (back-belly), and anterior-posterior (head-feet) axes, illustrated in <a class=\"xref target-figure\" title=\"Figure\u00a043.30.\u00a0\" href=\"#attachment_1420\">Figure 24.30<\/a>.<\/p>\n<figure id=\"attachment_1420\" aria-describedby=\"caption-attachment-1420\" style=\"width: 600px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_43_06_03.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1420\" src=\"https:\/\/pressbooks.bccampus.ca\/knowinghome\/wp-content\/uploads\/sites\/1064\/2020\/06\/Figure_43_06_03-1024x475-1.jpg\" alt=\"Figure_43_06_03\" width=\"600\" height=\"278\" \/><\/a><figcaption id=\"caption-attachment-1420\" class=\"wp-caption-text\">Figure 24.30.\u00a0 Animal bodies have three axes for symmetry. (credit: modification of work by NOAA)<\/figcaption><\/figure>\n<p><span id=\"m44850-fs-idp23643616\"> <\/span>How are these established? In one of the most seminal experiments ever to be carried out in developmental biology, Spemann and Mangold took dorsal cells from one embryo and transplanted them into the belly region of another embryo. They found that the transplanted embryo now had two notochords: one at the dorsal site from the original cells and another at the transplanted site. This suggested that the dorsal cells were genetically programmed to form the notochord and define the axis. Since then, researchers have identified many genes that are responsible for axis formation. Mutations in these genes leads to the loss of symmetry required for organism development.<\/p>\n<p><span id=\"m44850-fs-idp164017568\"> <\/span>Animal bodies have externally visible symmetry. However, the internal organs are not symmetric. For example, the heart is on the left side and the liver on the right. The formation of the central left-right axis is an important process during development. This internal asymmetry is established very early during development and involves many genes. Research is still ongoing to fully understand the developmental implications of these genes.<\/p>\n<h2>Summary<\/h2>\n<p>Organogenesis is the formation of organs from the germ layers. Each germ layer gives rise to specific tissue types. The first stage is the formation of the neural system in the ectoderm. The mesoderm gives rise to somites and the notochord. Formation of vertebrate axis is another important developmental stage.<\/p>\n<div class=\"title\">\n<div class=\"title\">\n<div class=\"bcc-box bcc-info\">\n<h3>Exercises<\/h3>\n<div class=\"section\">\n<div class=\"body\">\n<div id=\"m44850-fs-idm29405328\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n<ol>\n<li>Which of the following gives rise to the skin cells?\n<ol>\n<li>ectoderm<\/li>\n<li>endoderm<\/li>\n<li>mesoderm<\/li>\n<li>none of the above<\/li>\n<\/ol>\n<\/li>\n<li>The ribs form from the ________.\n<ol>\n<li>notochord<\/li>\n<li>neural plate<\/li>\n<li>neural tube<\/li>\n<li>somites<\/li>\n<\/ol>\n<\/li>\n<li>Explain how the different germ layers give rise to different tissue types.<\/li>\n<li>Explain the role of axis formation in development<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"cnx-eoc free-response\">\n<div id=\"m44850-fs-idp121762688\" class=\"exercise\">\n<div class=\"body\">\n<div id=\"m44850-fs-idp20676832\" class=\"solution labeled\">\n<div class=\"body\">\n<p><strong>Answers<\/strong><\/p>\n<ol>\n<li>A<\/li>\n<li>D<\/li>\n<li>Organs form from the germ layers through the process of differentiation. During differentiation, the embryonic stem cells express a specific set of genes that will determine their ultimate fate as a cell type. For example, some cells in the ectoderm will express the genes specific to skin cells. As a result, these cells will differentiate into epidermal cells. The process of differentiation is regulated by cellular signaling cascades.<\/li>\n<li>Animal bodies have lateral-medial (left-right), dorsal-ventral (back-belly), and anterior-posterior (head-feet) axes. The dorsal cells are genetically programmed to form the notochord and define the axis. There are many genes responsible for axis formation. Mutations in these genes lead to the loss of symmetry required for organism development.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"id862105\" class=\"glossary\" title=\"Glossary\">\n<div class=\"titlepage\">\n<div class=\"bcc-box bcc-success\">\n<h3>Glossary<\/h3>\n<dl>\n<dt><strong>morning sickness<\/strong><\/dt>\n<dd>condition in the mother during the first trimester; includes feelings of nausea<\/dd>\n<dt><strong>neural tube<\/strong><\/dt>\n<dd>tube-like structure that forms from the ectoderm and gives rise to the brain and spinal cord<\/dd>\n<dt><strong>oogenesis<\/strong><\/dt>\n<dd>process of producing haploid eggs<\/dd>\n<dt><strong>organogenesis<\/strong><\/dt>\n<dd>process of organ formation<\/dd>\n<dt><strong>oviduct<\/strong><\/dt>\n<dd>(also, fallopian tube) muscular tube connecting the uterus with the ovary area<\/dd>\n<dt><strong>somite<\/strong><\/dt>\n<dd>group of cells separated by small spaces that form from the mesoderm and give rise to connective tissue<\/dd>\n<\/dl>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"cnx-eoc summary\">\n<div class=\"cnx-eoc art-exercise\">\n<div class=\"section empty\">\n<div class=\"section empty\">\n<div class=\"section empty\">\n<div class=\"section\">\n<div class=\"body\">\n<div id=\"m44839-fs-idp69205744\" class=\"exercise\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":103,"menu_order":77,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-940","chapter","type-chapter","status-publish","hentry"],"part":1403,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/pressbooks\/v2\/chapters\/940","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/wp\/v2\/users\/103"}],"version-history":[{"count":2,"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/pressbooks\/v2\/chapters\/940\/revisions"}],"predecessor-version":[{"id":1457,"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/pressbooks\/v2\/chapters\/940\/revisions\/1457"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/pressbooks\/v2\/parts\/1403"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/pressbooks\/v2\/chapters\/940\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/wp\/v2\/media?parent=940"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/pressbooks\/v2\/chapter-type?post=940"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/wp\/v2\/contributor?post=940"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/biologyh5p\/wp-json\/wp\/v2\/license?post=940"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}