Re: When dose a recessive allele take ove the dominant allele

     I am sorry to say that your parents may have misunderstood the genetic 
explaination of the disease. A recessive allele never takes over a dominant 
allele. 
     Cerebral Palsy, however, is mostly caused by infection, stroke (due to 
many rasons, such as abnormal blood cells),oxygen loss during pregnancy or 
child birth, jaundice, and Rh incompatibility. Thus Cerebral palsy seems to 
have no direct genetic component, however there can be an indirect genetic 
component such as the abnormal blood cells mentioned above.
     To talk about Anglemens Syndrome: 

"Genetic imprinting-
Differential modification of the expression of genes depending upon whether 
they are inherited from the mother or the father.  This affects only 
certain segments of the human genetic complement,including PWS 
(Prader-willi Syndrome, see below) and Angelman syndrome on chromosome 
15q."

"Anglemens Syndrome-
A rare syndrome reported in 1965 by Dr. H. Angelman and associated with a 
chromosome 15 deletion similar to that seen in PWS. In AS, however, the 
deletion is seen on the chromosome contributed by the mother, whereas those 
with PWS lack certain genes from the father. The clinical problems and 
appearance of AS and PWS are distinctly different. These two syndromes 
represent the first examples in humans of genetic imprinting."

The above was copied (with modifications by me) from the following site:  
http://www.pwsausa.org/

Genetic imprinting is linked to AS. If the gene 15q11 is lost from the 
mothers side the disease is called Anglemens syndrome. If 15q11 is lost 
from the fathers side the disease is called Prader-willi Syndrome. So, in 
this case there is little to do with dominance or recessiveness. It mainly 
has to do with which parent the active or inactive gene comes from. For 
example: If a gene is passed through an egg it may always be inactivated, 
if a gene is passed through a sperm it may always be active - or vice 
versa.

References and links are below. Enjoy!
 http://w
ww.genetics.com.au/genetics/resource/factsht/9.html
 ht
tp://www-personal.umd.umich.edu/~jcthomas/JCTHOMAS/1997%20Case%
20Studies/WA%20Hiltunen.html
 http://www.cerebralpalsy.or
g/about-2.htm