# Homework Help: Huntington's Disease

1. Nov 27, 2007

### glxvr6turbo

A man in his early twenties who is normal learns that his father has developed Huntington's Disease, a rare, fatal disease caused by a dominant allele, which usually manifests itself in middle age (since the disease is rare, it is safe to assume that he is heterozygous). What is the probability that the younger man wil also develop the symptons later in life? (His mother does not carry a dominant allele.)

2. Dec 13, 2007

### Ouabache

Welcome to Physicsforums!! If you've already looked around, I believe you will find some very interesting and informative discussions here.
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To get you started: what do you think the genotypes are of the young man's father and mother with respect to the gene discussed?

3. Jan 12, 2009

### mhwebb03

It is a literal 50% chance of developing the disease. Let's say H represents the allele for Huntington's.. and h represents normal. Then the father would be Hh, and the mother would be hh. Then in having a child, there is a 50% chance of the child being Hh, 50% chance of the child being hh. (we can determine this probability using a punnett square)