Identify the non-Mendelian mode of inheritance for each of the 	
	following: 
	a.  A woman from a family with normal cholesterol marries a 	
            man with no L.D.L receptors, and all their children have 	        
	    cholesterol levels twice the normal of their mother.
	b.  In humans, skin color follows a bell-shaped curve, with very 	   
few people having very dark or very fair skin, most people have
            a medium shade.
	c.  Duchenne muscular dystrophy is almost always limited to boys, who 
	    inherit it from their non-affected mothers, who are heterozygous. 	
	d.  Evan though sickle-cell anemia is due to a single allele, it 	   
causes many phenotypic changes in those affected.
	e.  A white cow crossed with a red bull yields roan claves.

Hi Orca777,

Non-Mendelian inheritance modes are very interesting, I think, and
show that genetics are much more complex than we learn in elementary
school!  Here are my best answers for your five questions:

a: Incomplete dominance - The heterozygous condition is halfway
between each homozygous phenotype
(http://www.ucl.ac.uk/~ucbhjow/bmsi/bmsi_3.html) - note that all of
the children of an HH woman and an hh man will be Hh.

b: Multifactorial inheritance - several genes control this phenotype
(http://www.medterms.com/script/main/art.asp?articlekey=8928). 
Intelligence and eye color are also examples of this kind of
inheritance.

c: Sex-linked inheritance - recessive genes on the X chromosome act
dominant in boys (http://www.accessexcellence.org/AB/GG/sex.html). 
Male-pattern baldness is another example of this kind of inheritance

d: Pleiotropy - alleles have effects on multiple phenotypic traits
(http://www.sci.sdsu.edu/classes/biology/bio100/vandergast/lecture%206.html,
scroll down to #3).  I'll also note that sickle cell anemia shows
incomplete dominance as well, since heterozygous individuals have half
of their cells sickling, and half not.

e: Incomplete dominance - the heterozygous genotype results in a
phenotype halfway between the homozygous ones
(http://www.oglethorpe.edu/faculty/~d_schadler/lecture19.htm) - note
that the white cow is homozygous for the no-pigment allele (call it
rr) and the red bull is homozygous for the pigment allele (RR), so all
calves will be Rr.


The other major non-Mendelian mode of inheritance is codominance,
which is generally explained with blood types (AB, O, A, B).

I found the above websites to explain each example by doing a basic
Google search for "inheritance mendelian" and combined it with each
example ("LDL cholesterol", "skin color", "duchenne", "sickle-cell
anemia", "roan").

Librariankt