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#1




Autosomal dominant disorder and normal offspring
A man and woman are both affected by an autosomal dominant disorder that has 80% penetrance. They are both heterozygotes for the diseasecausing mutation. What is the probability that they will produce phenotypically normal offspring?
A) 20% B) 25% C) 40% D) 60% E) 80% 
#4




If you work out a punnett square then the chance of a normal child is 25%.
But Im confused about the 80% penetrance. Does that mean you subtract 20% (10080) of 25% ? .. so 25% x 0.2 = 5%. Therefore the probability to have a normal child will be 20%. 
The above post was thanked by:  
bebix (07122011) 
#6




Quote:
but offspings' chance of having disease = 75 %!!!... phenotypically chance of having disease = 75 % x 80% =0.6 
#7




chances of offspring to carry abnormal genes is 75%
if the abnormal gene does not express itself, then there is no disease manifestations. so when you say disease, it depends on whether you mean genotype or phenotype 
#8




80% x 1/4 ( which represent the normal phenotype ) = 20% ...
Im not good at this,, i just try...  A  a AA A  Aa aA a aa This disease is DOMINANT which means just 1 alele is require to express the disease so 3/4 are Sicks 1/4 is normal... Please if im wrong explain it... =) So According to my plots Answer is A 
#9




Quote:
If both parent are heterozygotes, there is a 75% chance that their offspring will receive one or two copies of the diseasecausing gene. With 80% penetrance, the probability that the offspring will be affected (phenotypically) is 0.75 * 0.8 = 60%. The probability that the offspring will be phenotypically normal is 1  0.6 = 0.4 or 40% 
#10




Thanks Bebix....=)

#11




Quote:

The above post was thanked by:  
drgsarunprasath (07122011) 
#12




Quote:

#13




two ways to answer this question:
Aa x Aa = AA Aa Aa aa 80% penetrance a) 0.75 * 0.80 = 60% affected (phenotypically) 10060 = 40% "normal" b) 0.25 (aa) * [0.75 * 0.2] where, [0.75 * 0.2] = phenotypically normal = 40% 
The above post was thanked by:  
drgsarunprasath (07122011), drortho (11252011), Hope2Pass (07122011), monsalg2502 (08242011) 
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