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<TITLE>Human fertilization - Wikipedia</TITLE>

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<H1 id="firstHeading" class="firstHeading" lang="en">Human fertilization</H1>			<DIV id="bodyContent" class="mw-body-content">
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<TD style="padding-top:0.4em;line-height:1.2em">Part of <A href="/wiki/Category:Human_development" title="Category:Human development">a series</A> on</TD>
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<TR>
<TH class="navbox-title" style="padding:0.2em 0.4em 0.2em;padding-top:0;font-size:145%;line-height:1.2em"><B><A href="/wiki/Human_development_(biology)" title="Human development (biology)">Human growth<BR />
and development</A></B></TH>
</TR>
<TR>
<TD style="padding:0.2em 0 0.4em"><A href="/wiki/File:Views_of_a_Foetus_in_the_Womb_detail.jpg" class="image"><IMG alt="Views of a Foetus in the Womb detail.jpg" src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2a/Views_of_a_Foetus_in_the_Womb_detail.jpg/100px-Views_of_a_Foetus_in_the_Womb_detail.jpg" width="100" height="139" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2a/Views_of_a_Foetus_in_the_Womb_detail.jpg/150px-Views_of_a_Foetus_in_the_Womb_detail.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2a/Views_of_a_Foetus_in_the_Womb_detail.jpg/200px-Views_of_a_Foetus_in_the_Womb_detail.jpg 2x" data-file-width="400" data-file-height="556" /></A></TD>
</TR>
<TR>
<TH class="navbox-abovebelow" style="padding:0.1em">Stages</TH>
</TR>
<TR>
<TD style="padding:0 0.1em 0.4em;padding:0.15em 0.5em 0.6em;">
<UL>
<LI><A href="/wiki/Human_embryogenesis" title="Human embryogenesis">Human embryogenesis</A></LI>
<LI><A href="/wiki/Fetus" title="Fetus">Fetus</A></LI>
<LI><A href="/wiki/Infant" title="Infant">Infant</A></LI>
<LI><A href="/wiki/Toddler" title="Toddler">Toddler</A></LI>
<LI><A href="/wiki/Early_childhood" title="Early childhood">Early childhood</A></LI>
<LI><A href="/wiki/Child" title="Child">Child</A></LI>
<LI><A href="/wiki/Preadolescence" title="Preadolescence">Preadolescence</A></LI>
<LI><A href="/wiki/Adolescence" title="Adolescence">Adolescence</A></LI>
<LI><A href="/wiki/Adult" title="Adult">Adult</A></LI>
<LI><A href="/wiki/Middle_age" title="Middle age">Middle age</A></LI>
<LI><A href="/wiki/Old_age" title="Old age">Old age</A></LI>
</UL>
</TD>
</TR>
<TR>
<TH class="navbox-abovebelow" style="padding:0.1em">Biological milestones</TH>
</TR>
<TR>
<TD style="padding:0 0.1em 0.4em;padding:0.15em 0.5em 0.6em;">
<UL>
<LI><A class="mw-selflink selflink">Fertilization</A></LI>
<LI><A href="/wiki/Childbirth" title="Childbirth">Childbirth</A></LI>
<LI><A href="/wiki/Gross_motor_skill#Learning_to_walk" title="Gross motor skill">Walking</A></LI>
<LI><A href="/wiki/Language_acquisition" title="Language acquisition">Language acquisition</A></LI>
<LI><A href="/wiki/Puberty" title="Puberty">Puberty</A></LI>
<LI><A href="/wiki/Menopause" title="Menopause">Menopause</A></LI>
<LI><A href="/wiki/Ageing" title="Ageing">Ageing</A></LI>
<LI><A href="/wiki/Death" title="Death">Death</A></LI>
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<TR>
<TH class="navbox-abovebelow" style="padding:0.1em"><A href="/wiki/Developmental_psychology" title="Developmental psychology">Development and psychology</A></TH>
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<UL>
<LI><A href="/wiki/Prenatal_and_perinatal_psychology" title="Prenatal and perinatal psychology">Pre- and perinatal</A></LI>
<LI><A href="/wiki/Child_development_stages" title="Child development stages">Infant and child</A></LI>
<LI><A href="/wiki/Adolescence#psychology" title="Adolescence">Adolescent</A></LI>
<LI><A href="/wiki/Positive_Youth_Development" class="mw-redirect" title="Positive Youth Development">Youth</A></LI>
<LI><A href="/wiki/Young_adult_(psychology)" title="Young adult (psychology)">Young adult</A></LI>
<LI><A href="/wiki/Adult_development" title="Adult development">Adult</A></LI>
<LI><A href="/wiki/Maturity_(psychological)" title="Maturity (psychological)">Maturity</A></LI>
</UL>
</TD>
</TR>
<TR>
<TH class="navbox-abovebelow" style="padding:0.1em">
<DIV style="padding:0.1em 0;line-height:1.2em;"><A href="/wiki/Developmental_stage_theories" title="Developmental stage theories">Developmental stage theories</A></DIV>
</TH>
</TR>
<TR>
<TD style="padding:0 0.1em 0.4em;padding:0.15em 0.5em 0.6em;">
<UL>
<LI><A href="/wiki/Attachment_theory" title="Attachment theory">Attachment</A></LI>
<LI><A href="/wiki/Ecological_systems_theory" title="Ecological systems theory">Ecological</A></LI>
<LI><A href="/wiki/Erikson%27s_stages_of_psychosocial_development" title="Erikson's stages of psychosocial development">Psychosocial</A></LI>
<LI><A href="/wiki/Psychosexual_development" title="Psychosexual development">Psychosexual development</A></LI>
<LI><A href="/wiki/Lawrence_Kohlberg%27s_stages_of_moral_development" title="Lawrence Kohlberg's stages of moral development">Moral</A></LI>
<LI><A href="/wiki/Piaget%27s_theory_of_cognitive_development" title="Piaget's theory of cognitive development">Cognitive</A></LI>
<LI><A href="/wiki/Cultural-historical_psychology" title="Cultural-historical psychology">Cultural-historical</A></LI>
<LI><A href="/wiki/Evolutionary_developmental_psychology" title="Evolutionary developmental psychology">Evolutionary</A></LI>
</UL>
</TD>
</TR>
<TR>
<TD style="padding:0.3em 0.4em 0.3em;font-weight:bold;border-top:1px solid #aaa;border-bottom:1px solid #aaa;">
<UL>
<LI><A href="/wiki/File:Human.png" class="image"><IMG alt="Human.png" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Human.png/13px-Human.png" width="13" height="16" class="noviewer" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Human.png/20px-Human.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Human.png/27px-Human.png 2x" data-file-width="1051" data-file-height="1258" /></A> <A href="/wiki/Portal:Human_body" title="Portal:Human body">Human body portal</A></LI>
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<LI class="nv-view"><A href="/wiki/Template:Human_growth_and_development_sidebar" title="Template:Human growth and development sidebar"><ABBR title="View this template">v</ABBR></A></LI>
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<LI class="nv-edit"><A class="external text" href="//en.wikipedia.org/w/index.php?title=Template:Human_growth_and_development_sidebar&action=edit"><ABBR title="Edit this template">e</ABBR></A></LI>
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<DIV class="thumb tright">
<DIV class="thumbinner" style="width:402px;"><A href="/wiki/File:Acrosome_reaction_diagram_en.svg" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/8/83/Acrosome_reaction_diagram_en.svg/400px-Acrosome_reaction_diagram_en.svg.png" width="400" height="282" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/83/Acrosome_reaction_diagram_en.svg/600px-Acrosome_reaction_diagram_en.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/83/Acrosome_reaction_diagram_en.svg/800px-Acrosome_reaction_diagram_en.svg.png 2x" data-file-width="688" data-file-height="485" /></A>
<DIV class="thumbcaption">
<DIV class="magnify"><A href="/wiki/File:Acrosome_reaction_diagram_en.svg" class="internal" title="Enlarge"></A></DIV>
The <A href="/wiki/Acrosome_reaction" title="Acrosome reaction">acrosome reaction</A> for a <A href="/wiki/Sea_urchin" title="Sea urchin">sea urchin</A>, a similar process. Note that the picture shows several stages of one and the same <A href="/wiki/Spermatozoon" title="Spermatozoon">spermatozoon</A> - only one penetrates the <A href="/wiki/Ovum" class="mw-redirect" title="Ovum">ovum</A></DIV>
</DIV>
</DIV>
<DIV class="thumb tright">
<DIV class="thumbinner" style="width:222px;"><A href="/wiki/File:Blausen_0404_Fertilization.png" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/7/79/Blausen_0404_Fertilization.png/220px-Blausen_0404_Fertilization.png" width="220" height="170" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/79/Blausen_0404_Fertilization.png/330px-Blausen_0404_Fertilization.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/79/Blausen_0404_Fertilization.png/440px-Blausen_0404_Fertilization.png 2x" data-file-width="3300" data-file-height="2550" /></A>
<DIV class="thumbcaption">
<DIV class="magnify"><A href="/wiki/File:Blausen_0404_Fertilization.png" class="internal" title="Enlarge"></A></DIV>
Illustration depicting ovulation and fertilization.</DIV>
</DIV>
</DIV>
<P><B>Human fertilization</B> is the union of a human <A href="/wiki/Ovum" class="mw-redirect" title="Ovum">egg</A> and <A href="/wiki/Spermatozoon" title="Spermatozoon">sperm</A>, usually occurring in the <A href="/wiki/Ampulla_of_fallopian_tube" class="mw-redirect" title="Ampulla of fallopian tube">ampulla of the fallopian tube</A>. The result of this union is the production of a <A href="/wiki/Zygote" title="Zygote">zygote</A> cell, or fertilized egg, initiating <A href="/wiki/Prenatal_development" title="Prenatal development">prenatal development</A>. Scientists discovered the dynamics of <A href="/wiki/Human" title="Human">human</A> fertilization in the nineteenth century.<SUP id="cite_ref-1" class="reference"><A href="#cite_note-1">[1]</A></SUP></P>
<P>The process of <A href="/wiki/Fertilization" class="mw-redirect" title="Fertilization">fertilization</A> involves a sperm fusing with an ovum. The most common sequence begins with <A href="/wiki/Ejaculation" title="Ejaculation">ejaculation</A> during <A href="/wiki/Sexual_intercourse" title="Sexual intercourse">copulation</A>, follows with <A href="/wiki/Ovulation" title="Ovulation">ovulation</A>, and finishes with fertilization. Various exceptions to this sequence are possible, including <A href="/wiki/Artificial_insemination" title="Artificial insemination">artificial insemination</A>, <A href="/wiki/In_vitro_fertilization" class="mw-redirect" title="In vitro fertilization"><I>in vitro</I> fertilization</A>, external ejaculation without copulation, or copulation shortly after ovulation.<SUP id="cite_ref-2" class="reference"><A href="#cite_note-2">[2]</A></SUP><SUP id="cite_ref-3" class="reference"><A href="#cite_note-3">[3]</A></SUP><SUP id="cite_ref-4" class="reference"><A href="#cite_note-4">[4]</A></SUP> Upon encountering the secondary oocyte, the acrosome of the sperm produces enzymes which allow it to burrow through the outer <A href="/wiki/Egg_jelly" title="Egg jelly">jelly coat</A> of the egg. The sperm plasma then fuses with the egg's plasma membrane, the sperm head disconnects from its flagellum and the egg travels down the Fallopian tube to reach the uterus.</P>
<P>In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside the womb, <I><A href="/wiki/In_vitro" title="In vitro">in vitro</A></I>.</P>
<P></P>
<DIV id="toc" class="toc">
<DIV class="toctitle" lang="en" dir="ltr" xml:lang="en">
<H2>Contents</H2>
<SPAN class="toctoggle"> [<A role="button" tabindex="0" class="togglelink">hide</A>] </SPAN></DIV>
<UL>
<LI class="toclevel-1 tocsection-1"><A href="#Anatomy"><SPAN class="tocnumber">1</SPAN> <SPAN class="toctext">Anatomy</SPAN></A>
<UL>
<LI class="toclevel-2 tocsection-2"><A href="#Corona_radiata"><SPAN class="tocnumber">1.1</SPAN> <SPAN class="toctext">Corona radiata</SPAN></A></LI>
<LI class="toclevel-2 tocsection-3"><A href="#Cone_of_attraction_and_perivitelline_membrane"><SPAN class="tocnumber">1.2</SPAN> <SPAN class="toctext">Cone of attraction and perivitelline membrane</SPAN></A></LI>
<LI class="toclevel-2 tocsection-4"><A href="#Sperm_preparation"><SPAN class="tocnumber">1.3</SPAN> <SPAN class="toctext">Sperm preparation</SPAN></A></LI>
<LI class="toclevel-2 tocsection-5"><A href="#Zona_pellucida"><SPAN class="tocnumber">1.4</SPAN> <SPAN class="toctext">Zona pellucida</SPAN></A>
<UL>
<LI class="toclevel-3 tocsection-6"><A href="#Cortical_reaction"><SPAN class="tocnumber">1.4.1</SPAN> <SPAN class="toctext">Cortical reaction</SPAN></A></LI>
</UL>
</LI>
</UL>
</LI>
<LI class="toclevel-1 tocsection-7"><A href="#Fusion"><SPAN class="tocnumber">2</SPAN> <SPAN class="toctext">Fusion</SPAN></A>
<UL>
<LI class="toclevel-2 tocsection-8"><A href="#Cell_membranes"><SPAN class="tocnumber">2.1</SPAN> <SPAN class="toctext">Cell membranes</SPAN></A></LI>
<LI class="toclevel-2 tocsection-9"><A href="#Transformations"><SPAN class="tocnumber">2.2</SPAN> <SPAN class="toctext">Transformations</SPAN></A></LI>
<LI class="toclevel-2 tocsection-10"><A href="#Replication"><SPAN class="tocnumber">2.3</SPAN> <SPAN class="toctext">Replication</SPAN></A></LI>
<LI class="toclevel-2 tocsection-11"><A href="#Mitosis"><SPAN class="tocnumber">2.4</SPAN> <SPAN class="toctext">Mitosis</SPAN></A></LI>
</UL>
</LI>
<LI class="toclevel-1 tocsection-12"><A href="#Fertilization_age"><SPAN class="tocnumber">3</SPAN> <SPAN class="toctext">Fertilization age</SPAN></A></LI>
<LI class="toclevel-1 tocsection-13"><A href="#Diseases"><SPAN class="tocnumber">4</SPAN> <SPAN class="toctext">Diseases</SPAN></A></LI>
<LI class="toclevel-1 tocsection-14"><A href="#See_also"><SPAN class="tocnumber">5</SPAN> <SPAN class="toctext">See also</SPAN></A></LI>
<LI class="toclevel-1 tocsection-15"><A href="#References"><SPAN class="tocnumber">6</SPAN> <SPAN class="toctext">References</SPAN></A></LI>
<LI class="toclevel-1 tocsection-16"><A href="#External_links"><SPAN class="tocnumber">7</SPAN> <SPAN class="toctext">External links</SPAN></A></LI>
</UL>
</DIV>
<P></P>
<H2><SPAN class="mw-headline" id="Anatomy">Anatomy</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=1" title="Edit section: Anatomy">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<H3><SPAN class="mw-headline" id="Corona_radiata">Corona radiata</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=2" title="Edit section: Corona radiata">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<P>The sperm binds through the <A href="/wiki/Corona_radiata_(embryology)" title="Corona radiata (embryology)">corona radiata</A>, a layer of follicle cells on the outside of the secondary <A href="/wiki/Oocyte" title="Oocyte">oocyte</A>. Fertilization occurs when the nucleus of both a sperm and an egg fuse to form a diploid cell, known as <A href="/wiki/Zygote" title="Zygote">zygote</A>. The successful fusion of gametes forms a new organism.</P>
<H3><SPAN class="mw-headline" id="Cone_of_attraction_and_perivitelline_membrane">Cone of attraction and perivitelline membrane</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=3" title="Edit section: Cone of attraction and perivitelline membrane">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<P>Where the spermatozoon is about to pierce, the yolk (<A href="/wiki/Ooplasm" class="mw-redirect" title="Ooplasm">ooplasm</A>) is drawn out into a conical elevation, termed the cone of attraction or reception cone. Once the spermatozoon has entered, the peripheral portion of the yolk changes into a membrane, the perivitelline membrane, which prevents the passage of additional spermatozoa.<SUP id="cite_ref-5" class="reference"><A href="#cite_note-5">[5]</A></SUP></P>
<H3><SPAN class="mw-headline" id="Sperm_preparation">Sperm preparation</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=4" title="Edit section: Sperm preparation">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<DIV role="note" class="hatnote navigation-not-searchable">Further information: <A href="/wiki/Acrosome_reaction" title="Acrosome reaction">Acrosome reaction</A></DIV>
<P>At the beginning of the process, the sperm undergoes a series of changes, as freshly ejaculated sperm is unable or poorly able to fertilize.<SUP id="cite_ref-A_6-0" class="reference"><A href="#cite_note-A-6">[6]</A></SUP> The sperm must undergo <A href="/wiki/Capacitation" title="Capacitation">capacitation</A> in the female's reproductive tract over several hours, which increases its motility and destabilizes its membrane, preparing it for the <A href="/wiki/Acrosome_reaction" title="Acrosome reaction">acrosome reaction</A>, the enzymatic penetration of the egg's tough membrane, the <A href="/wiki/Zona_pellucida" title="Zona pellucida">zona pellucida</A>, which surrounds the oocyte.</P>
<H3><SPAN class="mw-headline" id="Zona_pellucida">Zona pellucida</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=5" title="Edit section: Zona pellucida">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<P>After binding to the corona radiata the sperm reaches the <A href="/wiki/Zona_pellucida" title="Zona pellucida">zona pellucida</A>, which is an extra-cellular matrix of glycoproteins. A special complementary molecule on the surface of the sperm head binds to a ZP3 glycoprotein in the zona pellucida. This binding triggers the acrosome to burst, releasing enzymes that help the sperm get through the zona pellucida.</P>
<P>Some sperm cells consume their <A href="/wiki/Acrosome" title="Acrosome">acrosome</A> prematurely on the surface of the egg cell, facilitating the penetration by other sperm cells. As a population, sperm cells have on average 50% genome similarity so the premature acrosomal reactions aid fertilization by a member of the same cohort.<SUP id="cite_ref-7" class="reference"><A href="#cite_note-7">[7]</A></SUP> It may be regarded as a mechanism of <A href="/wiki/Kin_selection" title="Kin selection">kin selection</A>.</P>
<P>Recent studies have shown that the egg is not passive during this process.<SUP id="cite_ref-8" class="reference"><A href="#cite_note-8">[8]</A></SUP><SUP id="cite_ref-9" class="reference"><A href="#cite_note-9">[9]</A></SUP></P>
<H4><SPAN class="mw-headline" id="Cortical_reaction">Cortical reaction</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=6" title="Edit section: Cortical reaction">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H4>
<P>Once the sperm cells find their way past the zona pellucida, the <A href="/wiki/Cortical_reaction" title="Cortical reaction">cortical reaction</A> occurs. Cortical granules inside the secondary oocyte fuse with the plasma membrane of the cell, causing enzymes inside these granules to be expelled by exocytosis to the zona pellucida. This in turn causes the glyco-proteins in the zona pellucida to cross-link with each other — i.e. the enzymes cause the ZP2 to <A href="/wiki/Hydrolyse" class="mw-redirect" title="Hydrolyse">hydrolyse</A> into ZP2f — making the whole matrix hard and impermeable to sperm. This prevents fertilization of an egg by more than one sperm. The cortical reaction and acrosome reaction are both essential to ensure that only one sperm will fertilize an egg.<SUP id="cite_ref-10" class="reference"><A href="#cite_note-10">[10]</A></SUP></P>
<H2><SPAN class="mw-headline" id="Fusion">Fusion</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=7" title="Edit section: Fusion">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<DIV class="thumb tright">
<DIV class="thumbinner" style="width:222px;"><A href="/wiki/File:Human_Fertilization.png" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Human_Fertilization.png/220px-Human_Fertilization.png" width="220" height="165" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Human_Fertilization.png/330px-Human_Fertilization.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Human_Fertilization.png/440px-Human_Fertilization.png 2x" data-file-width="960" data-file-height="720" /></A>
<DIV class="thumbcaption">
<DIV class="magnify"><A href="/wiki/File:Human_Fertilization.png" class="internal" title="Enlarge"></A></DIV>
Fertilization and implantation in humans.</DIV>
</DIV>
</DIV>
<P>After the sperm enters the cytoplasm of the oocyte (also called ovocyte), the tail and the outer coating of the sperm disintegrate and the cortical reaction takes place, preventing other sperm from fertilizing the same egg. The oocyte now undergoes its second meiotic division producing the haploid ovum and releasing a polar body. The sperm nucleus then fuses with the ovum, enabling fusion of their genetic material.</P>
<H3><SPAN class="mw-headline" id="Cell_membranes">Cell membranes</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=8" title="Edit section: Cell membranes">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<P>The fusion of <A href="/wiki/Cell_membrane" title="Cell membrane">cell membranes</A> of the secondary oocyte and sperm takes place.</P>
<H3><SPAN class="mw-headline" id="Transformations">Transformations</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=9" title="Edit section: Transformations">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<P>In preparation for the fusion of their genetic material both the oocyte and the sperm undergo transformations as a reaction to the fusion of cell membranes.</P>
<P>The <A href="/wiki/Oocyte" title="Oocyte">oocyte</A> completes its <A href="/wiki/Meiosis" title="Meiosis">second meiotic division</A>. This results in a mature <A href="/wiki/Ovum" class="mw-redirect" title="Ovum">ovum</A>. The nucleus of the oocyte is called a <A href="/wiki/Pronucleus" title="Pronucleus">pronucleus</A> in this process, to distinguish it from the nuclei that are the result of fertilization.</P>
<P>The sperm's tail and <A href="/wiki/Mitochondria" class="mw-redirect" title="Mitochondria">mitochondria</A> degenerate with the formation of the male <A href="/wiki/Pronucleus" title="Pronucleus">pronucleus</A>. This is why all mitochondria in humans are of maternal origin. Still, a considerable amount of <A href="/wiki/RNA" title="RNA">RNA</A> from the sperm is delivered to the resulting embryo and likely influences embryo development and the phenotype of the offspring.<SUP id="cite_ref-11" class="reference"><A href="#cite_note-11">[11]</A></SUP></P>
<H3><SPAN class="mw-headline" id="Replication">Replication</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=10" title="Edit section: Replication">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<P>The pronuclei migrate toward the center of the oocyte, rapidly replicating their <A href="/wiki/DNA" title="DNA">DNA</A> as they do so to prepare the zygote for its first <A href="/wiki/Mitotic" class="mw-redirect" title="Mitotic">mitotic</A> division.<SUP id="cite_ref-Marieb_12-0" class="reference"><A href="#cite_note-Marieb-12">[12]</A></SUP></P>
<H3><SPAN class="mw-headline" id="Mitosis">Mitosis</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=11" title="Edit section: Mitosis">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<P>Usually 23 chromosomes from <A href="/wiki/Spermatozoon" title="Spermatozoon">spermatozoon</A> and 23 chromosomes from egg cell <A href="/wiki/Karyogamy" title="Karyogamy">fuse</A> (half of <A href="/wiki/Spermatozoon" title="Spermatozoon">spermatozoons</A> carry X chromosome and the other half Y chromosome<SUP id="cite_ref-13" class="reference"><A href="#cite_note-13">[13]</A></SUP>). Their membranes dissolve, leaving no barriers between the male and female <A href="/wiki/Chromosome" title="Chromosome">chromosomes</A>. During this dissolution, a <A href="/wiki/Mitotic_spindle" class="mw-redirect" title="Mitotic spindle">mitotic spindle</A> forms between them. The spindle captures the chromosomes before they disperse in the egg cytoplasm. Upon subsequently undergoing mitosis (which includes pulling of chromatids towards centrioles in anaphase) the cell gathers genetic material from the male and female together. Thus, the first mitosis of the union of sperm and oocyte is the actual fusion of their chromosomes.<SUP id="cite_ref-Marieb_12-1" class="reference"><A href="#cite_note-Marieb-12">[12]</A></SUP></P>
<P>Each of the two daughter cells resulting from that mitosis has one replica of each chromatid that was replicated in the previous stage. Thus, they are genetically identical.</P>
<H2><SPAN class="mw-headline" id="Fertilization_age">Fertilization age</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=12" title="Edit section: Fertilization age">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<P>Fertilization is the event most commonly used to mark the <A href="/wiki/Origin_(mathematics)" title="Origin (mathematics)">zero point</A> in descriptions of <A href="/wiki/Prenatal_development" title="Prenatal development">prenatal development</A> of the embryo or fetus. The resultant age is known as <I>fertilization age</I>, <I>fertilizational age</I>, <I>embryonic age</I>, <I>fetal age</I> or <I>(intrauterine) developmental (IUD)<SUP id="cite_ref-14" class="reference"><A href="#cite_note-14">[14]</A></SUP> age</I>.</P>
<P><A href="/wiki/Gestational_age" title="Gestational age">Gestational age</A>, in contrast, takes the beginning of the last <A href="/wiki/Menstrual_period" class="mw-redirect" title="Menstrual period">menstrual period</A> (LMP) as the <A href="/wiki/Origin_(mathematics)" title="Origin (mathematics)">zero point</A>. By convention, gestational age is calculated by adding 14 days to fertilization age and vice versa.<SUP id="cite_ref-15" class="reference"><A href="#cite_note-15">[15]</A></SUP> In fact, however, fertilization usually occurs within a day of <A href="/wiki/Ovulation" title="Ovulation">ovulation</A>, which, in turn, occurs on average 14.6 days after the beginning of the preceding menstruation (LMP).<SUP id="cite_ref-Geirsson1991_16-0" class="reference"><A href="#cite_note-Geirsson1991-16">[16]</A></SUP> There is also considerable variability in this interval, with a 95% <A href="/wiki/Prediction_interval" title="Prediction interval">prediction interval</A> of the ovulation of 9 to 20 days after menstruation even for an average woman who has a mean LMP-to-ovulation time of 14.6.<SUP id="cite_ref-fehring2006_17-0" class="reference"><A href="#cite_note-fehring2006-17">[17]</A></SUP> In a reference group representing all women, the 95% prediction interval of the LMP-to-ovulation is 8.2 to 20.5 days.<SUP id="cite_ref-Geirsson1991_16-1" class="reference"><A href="#cite_note-Geirsson1991-16">[16]</A></SUP></P>
<P>The average time to birth has been estimated to be 268 days (38 weeks and two days) from <A href="/wiki/Ovulation" title="Ovulation">ovulation</A>, with a <A href="/wiki/Standard_deviation" title="Standard deviation">standard deviation</A> of 10 days or <A href="/wiki/Coefficient_of_variation" title="Coefficient of variation">coefficient of variation</A> of 3.7%.<SUP id="cite_ref-pmid23922246_18-0" class="reference"><A href="#cite_note-pmid23922246-18">[18]</A></SUP></P>
<P>Fertilization age is sometimes used postnatally (after birth) as well to estimate various risk factors. For example, it is a better predictor than postnatal age for risk of <A href="/wiki/Intraventricular_hemorrhage" title="Intraventricular hemorrhage">intraventricular hemorrhage</A> in <A href="/wiki/Preterm_birth" title="Preterm birth">premature babies</A> treated with <A href="/wiki/Extracorporeal_membrane_oxygenation" title="Extracorporeal membrane oxygenation">extracorporeal membrane oxygenation</A>.<SUP id="cite_ref-19" class="reference"><A href="#cite_note-19">[19]</A></SUP></P>
<H2><SPAN class="mw-headline" id="Diseases">Diseases</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=13" title="Edit section: Diseases">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<P>Various disorders can arise from defects in the fertilization process.</P>
<UL>
<LI><A href="/wiki/Polyspermy" title="Polyspermy">Polyspermy</A> results from multiple sperm fertilizing an egg.</LI>
</UL>
<P>However, some researchers have found<SUP class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><SPAN title="Sort of weasel words; needs ref or specify which researchers (June 2014)">citation needed</SPAN></A></I>]</SUP> that in rare pairs of fraternal twins, their origin might have been from the fertilization of one egg cell from the mother and eight sperm cells from the father. This possibility has been investigated by computer simulations of the fertilization process.</P>
<H2><SPAN class="mw-headline" id="See_also">See also</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=14" title="Edit section: See also">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<UL>
<LI><A href="/wiki/Spontaneous_conception" title="Spontaneous conception">Spontaneous conception</A>, the unassisted conception of a subsequent child after prior use of assisted reproductive technology</LI>
</UL>
<H2><SPAN class="mw-headline" id="References">References</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=15" title="Edit section: References">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<DIV class="reflist columns references-column-width" style="-moz-column-width: 30em; -webkit-column-width: 30em; column-width: 30em; list-style-type: decimal;">
<OL class="references">
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<LI id="cite_note-9"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-9"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Richard E. Jones and Kristin H. Lopez, Human Reproductive Biology, Third Edition, Elsevier, 2006, page 238</SPAN></LI>
<LI id="cite_note-10"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-10"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation web"><A rel="nofollow" class="external text" href="https://www.boundless.com/biology/embryogenesis/process-fertilization-1/fertilization-cortical-reaction/">"Fertilization: The Cortical Reaction"</A>. <I>Boundless</I>. Boundless<SPAN class="reference-accessdate">. Retrieved <SPAN class="nowrap">14 March</SPAN> 2013</SPAN>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Boundless&rft.atitle=Fertilization%3A+The+Cortical+Reaction&rft_id=https%3A%2F%2Fwww.boundless.com%2Fbiology%2Fembryogenesis%2Fprocess-fertilization-1%2Ffertilization-cortical-reaction%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHuman+fertilization" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-11"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-11"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Jodar, M.; Selvaraju, S.; Sendler, E.; Diamond, M. P.; Krawetz, S. A.; for the Reproductive Medicine Networks (2013). <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC3796946">"The presence, role and clinical use of spermatozoal RNAs"</A>. <I>Human Reproduction Update</I>. <B>19</B> (6): 604–624. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1093%2Fhumupd%2Fdmt031">10.1093/humupd/dmt031</A>. <A href="/wiki/PubMed_Central" title="PubMed Central">PMC</A> <SPAN class="plainlinks"><A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC3796946">3796946</A> <IMG alt="Freely accessible" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png" title="Freely accessible" width="9" height="14" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/14px-Lock-green.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/18px-Lock-green.svg.png 2x" data-file-width="512" data-file-height="813" /></SPAN>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/23856356">23856356</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Human+Reproduction+Update&rft.atitle=The+presence%2C+role+and+clinical+use+of+spermatozoal+RNAs&rft.volume=19&rft.issue=6&rft.pages=604-624&rft.date=2013&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3796946&rft_id=info%3Apmid%2F23856356&rft_id=info%3Adoi%2F10.1093%2Fhumupd%2Fdmt031&rft.aulast=Jodar&rft.aufirst=M.&rft.au=Selvaraju%2C+S.&rft.au=Sendler%2C+E.&rft.au=Diamond%2C+M.+P.&rft.au=Krawetz%2C+S.+A.&rft.au=for+the+Reproductive+Medicine+Networks&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3796946&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHuman+fertilization" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Marieb-12"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Marieb_12-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Marieb_12-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text">Marieb, Elaine M. <I>Human Anatomy and Physiology, 5th ed.</I> pp. 1119-1122 (2001). <A href="/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</A> <A href="/wiki/Special:BookSources/0-8053-4989-8" title="Special:BookSources/0-8053-4989-8">0-8053-4989-8</A></SPAN></LI>
<LI id="cite_note-13"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-13"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><A rel="nofollow" class="external free" href="https://www.genderselectionauthority.com/blog/five-facts-about-xx-or-xy">https://www.genderselectionauthority.com/blog/five-facts-about-xx-or-xy</A></SPAN></LI>
<LI id="cite_note-14"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-14"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Wagner F, Erdösová B, Kylarová D (December 2004). "Degradation phase of apoptosis during the early stages of human metanephros development". <I>Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub</I>. <B>148</B> (2): 255–6. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.5507%2Fbp.2004.054">10.5507/bp.2004.054</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/15744391">15744391</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Biomed+Pap+Med+Fac+Univ+Palacky+Olomouc+Czech+Repub&rft.atitle=Degradation+phase+of+apoptosis+during+the+early+stages+of+human+metanephros+development&rft.volume=148&rft.issue=2&rft.pages=255-6&rft.date=2004-12&rft_id=info%3Adoi%2F10.5507%2Fbp.2004.054&rft_id=info%3Apmid%2F15744391&rft.aulast=Wagner&rft.aufirst=F&rft.au=Erd%C3%B6sov%C3%A1%2C+B&rft.au=Kylarov%C3%A1%2C+D&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHuman+fertilization" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-15"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-15"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Robinson, H. P.; Fleming, J. E. E. (1975). "A Critical Evaluation of Sonar "crown-Rump Length" Measurements". <I>BJOG: an International Journal of Obstetrics and Gynaecology</I>. <B>82</B> (9): 702–710. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1111%2Fj.1471-0528.1975.tb00710.x">10.1111/j.1471-0528.1975.tb00710.x</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=BJOG%3A+an+International+Journal+of+Obstetrics+and+Gynaecology&rft.atitle=A+Critical+Evaluation+of+Sonar+%22crown-Rump+Length%22+Measurements&rft.volume=82&rft.issue=9&rft.pages=702-710&rft.date=1975&rft_id=info%3Adoi%2F10.1111%2Fj.1471-0528.1975.tb00710.x&rft.aulast=Robinson&rft.aufirst=H.+P.&rft.au=Fleming%2C+J.+E.+E.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHuman+fertilization" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Geirsson1991-16"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Geirsson1991_16-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Geirsson1991_16-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Geirsson RT (May 1991). "Ultrasound instead of last menstrual period as the basis of gestational age assignment". <I>Ultrasound Obstet Gynecol</I>. <B>1</B> (3): 212–9. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1046%2Fj.1469-0705.1991.01030212.x">10.1046/j.1469-0705.1991.01030212.x</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/12797075">12797075</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Ultrasound+Obstet+Gynecol&rft.atitle=Ultrasound+instead+of+last+menstrual+period+as+the+basis+of+gestational+age+assignment&rft.volume=1&rft.issue=3&rft.pages=212-9&rft.date=1991-05&rft_id=info%3Adoi%2F10.1046%2Fj.1469-0705.1991.01030212.x&rft_id=info%3Apmid%2F12797075&rft.au=Geirsson+RT&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHuman+fertilization" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN> <A rel="nofollow" class="external autonumber" href="http://onlinelibrary.wiley.com/doi/10.1046/j.1469-0705.1991.01030212.x/pdf">[1]</A></SPAN></LI>
<LI id="cite_note-fehring2006-17"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-fehring2006_17-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Derived from a <A href="/wiki/Standard_deviation" title="Standard deviation">standard deviation</A> in this interval of 2.6, as given in: <CITE class="citation journal">Fehring RJ, Schneider M, Raviele K (2006). "Variability in the phases of the menstrual cycle". <I>J Obstet Gynecol Neonatal Nurs</I>. <B>35</B> (3): 376–84. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1111%2Fj.1552-6909.2006.00051.x">10.1111/j.1552-6909.2006.00051.x</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/16700687">16700687</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=J+Obstet+Gynecol+Neonatal+Nurs&rft.atitle=Variability+in+the+phases+of+the+menstrual+cycle&rft.volume=35&rft.issue=3&rft.pages=376-84&rft.date=2006&rft_id=info%3Adoi%2F10.1111%2Fj.1552-6909.2006.00051.x&rft_id=info%3Apmid%2F16700687&rft.aulast=Fehring&rft.aufirst=RJ&rft.au=Schneider%2C+M&rft.au=Raviele%2C+K&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHuman+fertilization" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-pmid23922246-18"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-pmid23922246_18-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Jukic AM, Baird DD, Weinberg CR, McConnaughey DR, Wilcox AJ (2013). <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC3777570">"Length of human pregnancy and contributors to its natural variation"</A>. <I>Hum. Reprod</I>. <B>28</B> (10): 2848–55. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1093%2Fhumrep%2Fdet297">10.1093/humrep/det297</A>. <A href="/wiki/PubMed_Central" title="PubMed Central">PMC</A> <SPAN class="plainlinks"><A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC3777570">3777570</A> <IMG alt="Freely accessible" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png" title="Freely accessible" width="9" height="14" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/14px-Lock-green.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/18px-Lock-green.svg.png 2x" data-file-width="512" data-file-height="813" /></SPAN>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/23922246">23922246</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Hum.+Reprod.&rft.atitle=Length+of+human+pregnancy+and+contributors+to+its+natural+variation&rft.volume=28&rft.issue=10&rft.pages=2848-55&rft.date=2013&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3777570&rft_id=info%3Apmid%2F23922246&rft_id=info%3Adoi%2F10.1093%2Fhumrep%2Fdet297&rft.aulast=Jukic&rft.aufirst=AM&rft.au=Baird%2C+DD&rft.au=Weinberg%2C+CR&rft.au=McConnaughey%2C+DR&rft.au=Wilcox%2C+AJ&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3777570&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHuman+fertilization" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-19"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-19"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Alan H. Jobe, MD, PhD. <I>Post-fertilizational age and IVH in ECMO patients</I>. RadiologySource Volume 145, Issue 2, Page A2 (August 2004). PII: S0022-3476(04)00583-9. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="https://doi.org/10.1016%2Fj.jpeds.2004.07.010">10.1016/j.jpeds.2004.07.010</A>.</SPAN></LI>
</OL>
</DIV>
<H2><SPAN class="mw-headline" id="External_links">External links</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Human_fertilization&action=edit&section=16" title="Edit section: External links">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<UL>
<LI><A rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=BFrVmDgh4v4">Fertilization (Conception)</A></LI>
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<DIV id="Human_physiology_of_sexual_reproduction" style="font-size:114%;margin:0 4em"><A href="/wiki/Human_body" title="Human body">Human physiology</A> of <A href="/wiki/Human_reproduction" title="Human reproduction">sexual reproduction</A></DIV>
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<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Menstrual_cycle" title="Menstrual cycle">Menstrual cycle</A></TH>
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<LI><A href="/wiki/Menarche" title="Menarche">Menarche</A></LI>
<LI><A href="/wiki/Menstruation" title="Menstruation">Menstruation</A></LI>
<LI><A href="/wiki/Follicular_phase" title="Follicular phase">Follicular phase</A></LI>
<LI><A href="/wiki/Ovulation" title="Ovulation">Ovulation</A></LI>
<LI><A href="/wiki/Luteal_phase" title="Luteal phase">Luteal phase</A></LI>
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<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Gametogenesis" title="Gametogenesis">Gametogenesis</A></TH>
<TD class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Spermatogenesis" title="Spermatogenesis">Spermatogenesis</A> (<A href="/wiki/Spermatogonium" title="Spermatogonium">spermatogonium</A></LI>
<LI><A href="/wiki/Spermatocyte" title="Spermatocyte">spermatocyte</A></LI>
<LI><A href="/wiki/Spermatid" title="Spermatid">spermatid</A></LI>
<LI><A href="/wiki/Sperm" title="Sperm">sperm</A>)</LI>
<LI><A href="/wiki/Oogenesis" title="Oogenesis">Oogenesis</A> (<A href="/wiki/Oogonium" title="Oogonium">oogonium</A></LI>
<LI><A href="/wiki/Oocyte" title="Oocyte">oocyte</A></LI>
<LI><A href="/wiki/Immature_ovum" title="Immature ovum">ootid</A></LI>
<LI><A href="/wiki/Egg_cell" title="Egg cell">ovum</A>)</LI>
<LI><A href="/wiki/Germ_cell" title="Germ cell">Germ cell</A> (<A href="/wiki/Gonocyte" title="Gonocyte">gonocyte</A></LI>
<LI><A href="/wiki/Gamete" title="Gamete">gamete</A>)</LI>
</UL>
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<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Human_sexual_activity" title="Human sexual activity">Human sexual behavior</A></TH>
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<LI><A href="/wiki/Sexual_arousal" title="Sexual arousal">Sexual arousal</A></LI>
<LI><A href="/wiki/Sexual_intercourse" title="Sexual intercourse">Sexual intercourse</A></LI>
<LI><A href="/wiki/Masturbation" title="Masturbation">Masturbation</A></LI>
<LI><A href="/wiki/Erection" title="Erection">Erection</A></LI>
<LI><A href="/wiki/Orgasm" title="Orgasm">Orgasm</A></LI>
<LI><A href="/wiki/Ejaculation" title="Ejaculation">Ejaculation</A></LI>
<LI><A href="/wiki/Insemination" title="Insemination">Insemination</A></LI>
<LI><A class="mw-selflink selflink">Fertilisation</A>/<A href="/wiki/Fertility" title="Fertility">Fertility</A></LI>
<LI><A href="/wiki/Implantation_(human_embryo)" title="Implantation (human embryo)">Implantation</A></LI>
<LI><A href="/wiki/Pregnancy" title="Pregnancy">Pregnancy</A></LI>
<LI><A href="/wiki/Postpartum_period" title="Postpartum period">Postpartum period</A></LI>
<LI><A href="/wiki/Mechanics_of_human_sexuality" title="Mechanics of human sexuality">Mechanics of sex</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR>
<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Human_development_(biology)" title="Human development (biology)">Life span</A></TH>
<TD class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Prenatal_development" title="Prenatal development">Prenatal development</A>/<A href="/wiki/Sexual_dimorphism" title="Sexual dimorphism">Sexual dimorphism</A>/<A href="/wiki/Sexual_differentiation_in_humans" title="Sexual differentiation in humans">Sexual differentiation</A> (<A href="/wiki/Feminization_(biology)" title="Feminization (biology)">Feminization</A></LI>
<LI><A href="/wiki/Virilization" title="Virilization">Virilization</A>)</LI>
<LI><A href="/wiki/Puberty" title="Puberty">Puberty</A> (<A href="/wiki/Gonadarche" title="Gonadarche">Gonadarche</A></LI>
<LI><A href="/wiki/Pubarche" title="Pubarche">Pubarche</A></LI>
<LI><A href="/wiki/Menarche" title="Menarche">Menarche</A></LI>
<LI><A href="/wiki/Spermarche" title="Spermarche">Spermarche</A></LI>
<LI><A href="/wiki/Adrenarche" title="Adrenarche">Adrenarche</A>)</LI>
<LI><A href="/wiki/Advanced_maternal_age" title="Advanced maternal age">Maternal age</A> / <A href="/wiki/Paternal_age_effect" title="Paternal age effect">Paternal age</A></LI>
<LI><A href="/wiki/Menopause" title="Menopause">Climacteric</A> (<A href="/wiki/Menopause" title="Menopause">Menopause</A></LI>
<LI><A href="/wiki/Late-onset_hypogonadism" title="Late-onset hypogonadism">Late-onset hypogonadism</A>)</LI>
<LI><A href="/wiki/Tanner_scale" title="Tanner scale">Tanner scale</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR>
<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Egg" title="Egg">Egg</A></TH>
<TD class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
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document_title: Human fertilization

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token: <Tr>

token: <Td>

token: Part

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token: embryogenesis

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token: Infant

token: Toddler

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token: Preadolescence

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token: Adult

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token: Biological

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token: Childbirth

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token: acquisition

token: Puberty

token: Menopause

token: Ageing

token: Death

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question_text: name the process of fusion of an egg with a sperm