Huntington disease is a rare dominant condition in humans that results in a slow but inexorable deterioration of the nervous system. The disease shows what might be called age-dependent penetrance, which is to say that the probability that a person with the Huntington genotype will express the phenotype varies with age. Assume that 50% of those inheriting the HD allele will express the symptoms by age 40. Susan is a 35-yearold woman whose father has Huntington disease. She currently shows no symptoms. What is the probabbility that Susan will show symptoms in five years?

Neural Tube Defects (NTDs) are one of the most severe congenital malformations. A study was conducted to determine whether supplementation with folic acid or a mixture of seven other vitamins (A, D, B1, B2, B6, C, and nicotinamide) around the time of conception could prevent neural tube defects. A total of 1817 women at high risk of having a pregnancy with a neural tube defect (because of a previous affected pregnancy) were allocated at random to one of four groups: 1) folic acid; 2) other vitamins; 3) both; 4) neither. 1195 had a completed pregnancy; 27 of these had a known neural tube defect, 6 in the folic acid groups and 21 in the two other groups.  This resulted in a risk ratio= 0.28. Based on the results of the study, which of the following is an appropriate conclusion? a)There is no difference in the effect of folic acid on NTDs b) None of these c) Folic acid increases risk of NTDs d) Folic acid is protective against NTDs

Hemophilia, disease in which the blood lacks a clotting factor, is caused by an X linked recessive gene. Joe doe not have hemophilia and Lucille is heterozygous for the condition.  What is the chance that their MALE child will have hemophilia? (Note: you are calculating the probability for their MALE children only, in other words if they have 1 male child, what is the probability that he will be born with the disease?)     0%     1/4 or 25%     2/4 or 50%     3/4 or 75%     4/4 or 100%

The father of three sons and two daughters begins to show symptoms of Huntington disease. What is the probability that Sam, the man’s second oldest son (II-2), will suffer from the disease if he lives a normal life span? Sam’s mother and her ancestors do not have the disease. Sam's father was adopted, so we do not know his biological family history for Huntington disease. Explore all possible outcomes for Sam and explain your reasoning. What about the risk to Sam's sisters? Would that be the same or not?