Can anyone please help me with these genetic problems?

Question

1. karen and steve each have a sibling with sickle-cell disease. Neither Karen nor Steve nor any of their parents have the disease, and none of them have been tested to reveal sickle-cell trait. Based on this incomplete info, calculate the probability that if this couple has a child, the child will ahve sickle-cell disease.

2. Imagine that you are a genetic counselor, and a couple planning to start a family come to you for info. Charles was married once before, and he and his first wife had a child with cystic fibrosis. Thre brother of his current wife Elaine died of cystic fibrosis. What is the probability that Charles and Elaine will ahve a baby with cystic fibrosis? (Neither Charles nor Elaine has cystic fibrosis).

Thank you, any help will be appreicated!

Answer 1

I don't blame you for having trouble with these! The problem is that the questions don't provide complete information... in that sense it's a lot like real life BUT it makes it impossible to give precise answers to a homework problem!

1. We can't precisely answer question #1 because we don't know Karen or Steve's race. If they're African American, there is a chance that their child will have sickle cell disease. If they're not, the chance is essentially zero.

Also, even if you happen to know that they're African-American, a precise calculation as to the chances of them having a child with sickle cell disease isn't possible. The best you can do is to look up the prevalence of sickle cell trait in African American's and assign this probability to each of the grandparents. You will then calculate the probability that Karen inherits exactly one copy of the gene and that Steve inherits exactly one copy of the gene. Multiple these probabilities together and multiply the result by 1/4 (IF Karen and Steve have each inherited one copy of the gene than the probability that they'll have a child with sickle cell disease is 1/4).

2. Again, question #2 provides incomplete information. Cystic fibrosis (CF) is inherited as an autosomal recessive mutation. Thus, if Charles has had a child with CF but he himself does not, he must be homozygous for the mutation (i.e. a carrier).

If Elaine's brother had CF, there's a chance Elaine herself could be a carrier as well. The chances of this, however, depend on Elaine's family's history which is not provided in this question. If NEITHER of Elaine's parents had CF, they must both be carriers because her brother had cystic fibrosis so the chances that Elaine is also a carrier is 2/3 (the Punnett square run at the time of conception gives 1 chance out of 4 of being negative for CF, 2 chances out of 4 of being a carrier, and 1 chance out of 4 of having CF; however we already know she doesn't have CF so we can exclude that possibility so the chance that she's a CF carrier is actually 2 chances out of 3 or 2/3rds).

If ONE of Elaine's parents had CF and the other did not then that implies that the other parent must be a carrier. Interestingly, this means that the chances are 100% that Elaine is a carrier - again, the Punnett square done at conception gives 2 chances of 4 of being a carrier and 2 chances of 4 of having CF and 0 chances of 4 of not having the CF gene at all. Since we know that Elaine doesn't have CF, we know that she MUST be a carrier instead.

If BOTH of Elaine's parents had CF then she must have CF as well. But the question tells us that she doesn't so we can discard this possibility.

I sincerely hope this wasn't a high school level question! This is the sort of question with incomplete information that's usually answered by trained genetic counsellors...

Answer 2

1: Well, i recently learned that diabetes and sickle usually skip a generation and move to the next so there is a pretty good chance.

Answer 3

i might say that it does not instruct there grew to become into basically one unique guy. There could have been human beings concurrently modern in many countries, the two woman and male, no longer descended from Adam or Eve.