Re: Inherited Physical characteristics-cleft chin

	According to the Online Mendelian Inheritance in (Hu)Man (OMIM), cleft 
chin has been observed in several multigenerational families.  (http://
www3.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?119000)  However, most of the 
data appear to be anecdotal at best.  I'll try to sum up: the cleft chin 
trait is more frequent and more obvious in males than females.  It is also a 
qualitative trait: although most people seem to agree that Kirk Douglas and 
John Travolta have cleft chins, my labmates are less certain about Ben 
Affleck and Ted Turner.  This makes it even harder to study inheritance 
patterns.

	Anecdotal evidence suggests an inherited component, but given the 
variable nature of the trait I would be surprised if it follows clear 
Mendelian dominant or recessive transmission patterns.  Heck, even though 
Mendel's Law has been useful in a lot of ways, it isn't clearly applicable 
to most human traits; not even hair color, eye color and tongue curling 
ability have proven as simple as the A/B/O blood type system.  So I would be 
surprised if cleft chin was a clear cut case.  However, the likelihood that 
an individual will have a cleft chin is probably higher if he has a few 
close male blood relatives with cleft chins.  

	As for whether the trait tends to skip generations, without any clear 
knowledge of the inheritance mode for the trait I can't really say.  If it's 
recessive or X-linked, it certainly could skip generations.  Sorry i can't 
be of much more help: if you have a large family tree with both affected and 
unaffected males in it, it would be fun to do the study yourself.

	Chris Carlson
	peterpan@leland.stanford.edu