X-linked inheritance.
<P>
<lI> Fathers  usually  pass  a  recessive  allele  to his daughter as a
carrier.
<lI> The carrier has a 50% chance of passing the disease to her sons.
<lI> If the carrier marries an affected male, 50% of the offspring will
have the disorder.
<P>
   These  recessive  disorders  are more common in males than in females,
   since  females  have  2  X  chromosomes  and  need to be homozygous to
   express the trait.
<P>
   Exercise:  <A ClAsS=ACT Href="http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/activities/load.html?15&amp;B" oNClick="popact('http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/activities/load.html?15&amp;B');txtcolor('XLinked4','gray');return false;" Id=XLinked4><iMg sRc="/images/tutorial.gif" aLt='' boRDer=0></A>