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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>Specialized chromosomes determine sex :: DNA from the Beginning</title> <meta name="description" content="Study of meiosis revealed the chromosomal basis of sex." /> <link rel="preload" as="style" src="/css/main.css"> <link rel="preload" as="script" src="/js/swfobject.js"> <link rel="preload" as="script" src="/js/prototype-1.6.1.js"> <link href="/css/main.css" rel="stylesheet" type="text/css" /> <link href='https://fonts.googleapis.com/css?family=Droid+Serif' rel='stylesheet' type='text/css'/> <link href='https://fonts.googleapis.com/css?family=Droid+Sans' rel='stylesheet' type='text/css'/> <script type="text/javascript" src="/js/swfobject.js"></script> <script type="text/javascript" src="/js/prototype-1.6.1.js"></script> </head> <body> <div id="container"> <div id="content"> <div id="header"> <div class="rollover-home"> <a href="/" class="rollover-home" title="DNA from the Beginning Home"><span class="displace">Home</span></a> </div> </div>  <div id="content-container"> <h1><span> Concept 9</span> Specialized chromosomes determine sex.</h1> <div id="nav"> <ul> <li class="menu1"><a href="index.html" title="CONCEPT" ><span class="displace">CONCEPT</span></a></li> <li class="menu2"><a href="animation.html" title="ANIMATION"><span class="displace">ANIMATION</span></a></li> <li class="menu3"><a href="gallery.html" title="GALLERY"><span class="displace">GALLERY</span></a></li> <li class="menu4"><a href="av.html" title="VIDEO"><span class="displace">VIDEO</span></a></li> <li class="menu5"><a href="bio.html" title="BIO"><span class="displace">BIO</span></a></li> <li class="menu6"><a href="problem.html" title="PROBLEM"><span class="displace">PROBLEM</span></a></li> <li class="menu7"><a href="links.html" title="LINKS" ><span class="displace">LINKS</span></a></li> </ul> <br class="clearfloat" /> </div> <div id="concept"> <img src="/images/9/concept9.jpg" class="concept-image" alt="Specialized chromosomes determine sex." /> <p>People had long philosophized about the observed differences between males and females of a species. If one considers sex a trait, or set of traits, then it followed that sex is inherited. In 1905, closer study of meiosis revealed the chromosomal basis of sex.</p> <p>Scientists noticed an oddball pair among the homologous chromosomes lined up at the cell equator during reduction division. One chromosome (X) was much bigger than the other (Y). In human beings, this mismatched pair of one X and one Y chromosome is seen exclusively in male cells. A matched pair of X chromosomes is found in female cells. Thus, XX chromosomes determine femaleness, and XY chromosomes determine maleness. Females produce only eggs with X chromosomes; males produce sperm with an X or a Y chromosome. </p> </div> </div> <br class="clearfloat" /> <div id="footer"> <ul> <li><a href="/">Home</a></li> <li><a href="/sitemap.html">Site Map</a></li> <li><a href="/scientists.html">Scientists</a></li> <li><a href="/glossary.html">Glossary</a></li> <li><a href="/feedback.html">Feedback</a></li> <li><a href="/awards.html">Awards</a></li> <li><a href="/credits.html">Credits</a></li> <li><a href="http://blogs.dnalc.org/dnaftb/" style="background-image:none;">Blog</a></li> </ul> <p> Funded by <a href="http://macyfoundation.org">The Josiah Macy, Jr. Foundation</a><br /> © 2002 - 2011, <a href="http://www.dnalc.org/"> DNA Learning Center</a>, <a href="https://www.cshl.edu/">Cold Spring Harbor Laboratory</a>. All rights reserved. </p> </div>  </div> <div id="sidebar"> <div id="search" > <form method="get" action="/search"> <div class="fieldHolder1"> <input type="search" id="q" name="q" placeholder="Search" onclick="this.value=''" value="" /> <img style="background-color:#9C0;" src="/images/general/search_icon.jpg" alt="Search" onclick="document.forms[0].submit()" /> </div> </form> </div>  <div id="sidebar"> <ul class="sections-side sections-side1a" style="padding-top: 56px; margin-top: 3px;"> <li ><a href="/1/"><img src="/images/thumbnails/1-thumb-sm.png" alt="1." />Children resemble their parents.</a></li> <li ><a href="/2/"><img src="/images/thumbnails/2-thumb-sm.png" alt="2." />Genes come in pairs.</a></li> <li ><a href="/3/"><img src="/images/thumbnails/3-thumb-sm.png" alt="3." />Genes don't blend.</a></li> <li ><a href="/4/"><img src="/images/thumbnails/4-thumb-sm.png" alt="4." />Some genes are dominant.</a></li> <li ><a href="/5/"><img src="/images/thumbnails/5-thumb-sm.png" alt="5." />Genetic inheritance follows rules.</a></li> <li ><a href="/6/"><img src="/images/thumbnails/6-thumb-sm.png" alt="6." />Genes are real things.</a></li> <li ><a href="/7/"><img src="/images/thumbnails/7-thumb-sm.png" alt="7." />All cells arise from pre-existing cells.</a></li> <li ><a href="/8/"><img src="/images/thumbnails/8-thumb-sm.png" alt="8." />Sex cells have one set of chromosomes; body cells have two.</a></li> <li ><a class="concept-highlight" href="/9/"><img src="/images/thumbnails/9-thumb-sm.png" alt="9." />Specialized chromosomes determine sex.</a></li> <li ><a href="/10/"><img src="/images/thumbnails/10-thumb-sm.png" alt="10." />Chromosomes carry genes.</a></li> <li ><a href="/11/"><img src="/images/thumbnails/11-thumb-sm.png" alt="11." />Genes get shuffled when chromosomes exchange pieces.</a></li> <li ><a href="/12/"><img src="/images/thumbnails/12-thumb-sm.png" alt="12." />Evolution begins with the inheritance of gene variations.</a></li> <li ><a href="/13/"><img src="/images/thumbnails/13-thumb-sm.png" alt="13." />Mendelian laws apply to human beings.</a></li> <li style="border-bottom: 1px solid #669;"><a href="/14/"><img src="/images/thumbnails/14-thumb-sm.png" alt="14." />Mendelian genetics cannot fully explain human health and behavior.</a></li> </ul> <ul class="menu-side"> <li class="section2"><a href="/15/index.html" title="Molecules of Genetics"><span class="displace">MOLECULES OF GENETICS</span></a></li> <li class="section3" ><a href="/29/index.html" title="Genetic Organization and Control"><span class="displace">GENETIC ORGANIZATION AND CONTROL</span></a></li> </ul> </div> </div>  <br class="clearfloat" /> </div>  <script type="text/javascript"> Event.observe(window, 'load', function() { var uri = '/9/index.html'; uri = uri.replace(/-\d/,''); $('nav').down().descendants().each(function(s) { if (s.nodeName == 'A') { if (s.href.match(uri)) { s.addClassName('current'); throw $break; } } }); }); </script> <script type="text/javascript"> var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-1818773-10']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = 'https://www.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); </script>  <script async src="https://www.googletagmanager.com/gtag/js?id=G-K6EHFCRJBP"></script> <script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'G-K6EHFCRJBP'); </script> </body> </html>