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Likelihood of inheriting autosomal dominant diseases

  • Thread starter Qube
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  • #1
Qube
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If one of your parents has Huntington's disease, you have a 50% chance of getting the gene for the disease.
This IS wrong. This only holds true if one of your parents is HETEROZYGOUS dominant.

Hh x hh => 50% chance of offspring having Huntington's disease.

However, if one of your parents is HOMOZYGOUS DOMINANT ..

HH x hh => 100% chance of offspring having Huntington's diseases.

Simple Punnett squares will verify the above.

Therefore, the probability should be 75% if one parent has Huntington's disease. Am I right?
 

Answers and Replies

  • #2
epenguin
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This IS wrong. This only holds true if one of your parents is HETEROZYGOUS dominant.

Hh x hh => 50% chance of offspring having Huntington's disease.

However, if one of your parents is HOMOZYGOUS DOMINANT ..

HH x hh => 100% chance of offspring having Huntington's diseases.

Simple Punnett squares will verify the above.

Therefore, the probability should be 75% if one parent has Huntington's disease. Am I right?
I don't know what you are quoting or context, but I'd guess this is an approximation based on homozygous being rare in the population.

The dynamics of Huntingdon's is a bit more complex than just the inheritance of a stable chromosome, and was explained in a recent thread on PF.
 
  • #3
Ygggdrasil
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You are making the faulty assumption that heterozygotes and homozygotes are equally abundant. In reality, the probability is 0.5p+(1-p), where p is the proportion of Huntington's patients who are heterozygous for the disease allele. As mentioned by epenguin, the disease allele is rare, so there are many more heterozygotes than homozygotes, and p~1.
 

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