The woman marked with a question mark is your friend. Knowing that you are taking Genetics, she comes to ask you for advice: she wants to have children, but is afraid that they will be sick with the disease. Her husband and her mother have no family history of HD. What is the probability that she is sick? What is the probability that her children will be, without knowing her own status regarding the disease?

The woman with the question mark is not sure if she has the HD disease,

The mother had no history of the disease this means she is not a carrier of the disease but we are not sure of the fathers genotype.

If the father is a carrier in an homozygous dominant form (aa) and the mother does not have the disease her. gentotype is AA

A A * aa

Aa Aa Aa Aa This means all their offspring will be Carrier of the disease because each parents contributes 50% of the gene their offspring is made of.

The probability that she is sick is 0% but she could be a carrot of the disease in an heterozygote form

If the woman who is a carrier (Aa) of the disease marries a man with no history of the disease (AA)

Aa * AA

I

AA AA Aa Aa

The probation of their offspring being a carrier in heterozygous form is 50% while the probability of the offspring being dominant of the disease is 0%. Hence, she should not be afraid since her mother and husband who could have contributed to determining the gene of this offspring are not carriers of this gene the offspring are safe.