Huntingtons disease is a neurological disorder that leads to...

Huntington’s disease is a neurological disorder that leads to progressive degeneration of brain cells, which in turn causes severe muscle spasms and personality disorders. The disease results from an autosomal dominant gene (H). This gene is a mutated copy of the gene for a protein called Huntingtin. Most people who have the disease show few or no symptoms until they are of middle age and have already had children, who may then also be stricken. Occasionally, the first sign of the disease in the next generation is seen in teenagers or even younger children. There is no effective treatment, and death comes in ten to fifteen years after the onset of symptoms. A woman who is heterozygous for Huntington’s disease marries a man who is homozygous recessive. What is the probability that this couple will have a child that will eventually develop Huntington’s disease? Select one: a. 0 percent b. 50 percent c. 100 percent d. 75 percent

Transcript

00:01 So in this question, we're looking at huntington's disease.

00:03 We're given some information on the background.

00:07 We're given that it's an autosomal dominant disorder, which means it's carried on the, we'll just put it, big h, right? so big h is huntington's h -u -n -t -i -n -g -t -o -n -s.

00:39 Little h is normal.

00:43 So if someone has huntington's, right, they had to inherit this from their mom or dad, not day, dad.

00:59 And they had to inherit that from their mom or dad.

01:04 So looking at this, is it possible for someone in this situation, 99 % of the time, is it possible in that 99 % of the time for someone to have huntington's in their parents to not have it.

01:22 99 % of the time that's not possible.

01:27 So it's not possible.

01:29 Another way to put that, 99 % of the time it's inherited.

01:33 So it's not possible for it to be inherited.

01:45 Okay, not possible.

01:50 The only other way would be if someone had huntington's, then it would have to be a mutation.

02:25 So when we look at that first question, i'm going to put a number one here for a question number one.

02:30 When we look at that first question, it's saying that this person, jonathan, recently tested positive for huntington's.

02:39 Was a condition never found in his parents or grandparents? so we have jonathan has huntington's not found in his parents.

03:10 Right? so what is that telling you already? he has huntington's.

03:13 It was not found in his parents.

03:14 Tells you that we're looking at this.