radio button "Checked" option not working

radio button "Checked" option not working

Could you please help me why my checked option in the following code is
not working?
<div class="span1">
<h7>&nbsp;&nbsp;&nbsp;&nbsp;Sex</h7>
<label class="radio">
<input id="pccf_sexMF" name="pccf_sexMF" value="M" type="radio"
checked class="span1" > M
</label>
<label class="radio">
<input id="sexMF" name="pccf_sexMF" value="F" type="radio"
class="span1"> F
</label>
</div>
Thanks