Problem: Huntington\'s Disease (read about it here http://www.ninds.nih.gov/diso

Question

Problem: Huntington's Disease (read about it here http://www.ninds.nih.gov/disorders/huntington/huntington.htm)

Maria is 42 years old. She is beginning to experience uncontrollable movements, and vividly recalls watching helplessly as her mother went through the final stages of Huntington's disease. She now suspects she may suffer a similar fate, and decides to get tested. The news is grim. Maria has the allele, and will develop Huntington's disease, despite being heterozygous.

Maria is married to Tom, and they have a son, whom is currently attending the University of Houston - Downtown. In addition to concerns about Maria's condition, they now wonder if their son could also have inherited the allele for Huntington's disease.

We will use H to designate the dominant, Huntington's allele, and h to represent the normal, recessive allele.

If their son inherited this allele, Huntington's disease will eventually set in as he ages. What is the chance that their son has this allele?

Fill out a Punnett square on your own paper to solve this problem.

0 (0%)

1/4 (25%)

1/2 (50%)

1 (100%)

Explanation / Answer

H is the dominant allele and h is the recessive allele for Huntington's disease

Maria has Huntington's disease = Hh( heterozygous) whereas Tom is normal = hh

   h             h

H       Hh            Hh

h       hh             hh

From Punnet square

Probability that their child has the allele = 2 / 4 = 1/2

So chances are 50%

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