Question

question 1. A microdeletion on 15q13.3 is associated with increased risk of intellectual disability, seizures, autism spectrum disorders, and schizophrenia. A recent study showed that penetrance for having at least one of these symptoms, assuming an average life span, is 40%. A 5 year old girl has recently been experiencing seizures, this deletion was detected in her, as well as her mother, and concluded to be the cause. What are the chances that her younger brother will experience one of the above symptoms in his life, assuming he lives to an old age?

Answer 1

The probability that the girl's brother shows symptoms = Prob. that the son inherits the micro deletion * Prob. that the son displays trait = 0.5 * 0.4 = 0.2

Given that the mother has the deletion, and she passes on either a normal chromosome, or a chromosome with the deletion, the probability of the son inheriting the affected allele is 1/2 or 0.5.

Given that the Penetrance of the disease is 40%, the probability of the child displaying the disorder is 0.4, thus the total probability of the child having the disease is 0.2