A healthy twenty-seven-year-old female presents to the physician for genetic counseling with her husband. They would like to become pregnant in the near future, but they have concerns that their offspring may develop cystic fibrosis. The wife’s sister has cystic fibrosis, an autosomal recessive disorder with an incidence of approximately 1 in 90,000. The husband’s history is noncontributory. what is the probability of the couple having an affected child?
Question
A healthy twenty-seven-year-old female presents to the physician for genetic counseling with her husband. They would like to become pregnant in the near future, but they have concerns that their offspring may develop cystic fibrosis. The wife’s sister has cystic fibrosis, an autosomal recessive disorder with an incidence of approximately 1 in 90,000. The husband’s history is noncontributory. what is the probability of the couple having an affected child?
Solution
Cystic fibrosis is an autosomal recessive disorder. This means that both parents must be carriers of the disease for a child to be affected.
Given that the woman's sister has cystic fibrosis, we know that both of her parents are carriers. Therefore, the woman has a 2 in 3 chance of being a carrier herself (since we know she does not have the disease).
The husband's history is noncontributory, which means we don't have any information suggesting he is a carrier. Given the incidence of cystic fibrosis is 1 in 90,000, we can estimate the frequency of carriers in the population. Using the Hardy-Weinberg equation (p^2 + 2pq + q^2 = 1), where q^2 is the incidence of the disease, we can calculate q (the frequency of the recessive allele in the population) and 2pq (the frequency of carriers in the population).
q^2 = 1/90,000 q = sqrt(1/90,000) = 0.0033 2pq = 2 * (1 - 0.0033) * 0.0033 = 0.0066
So, the husband has a 0.0066 chance of being a carrier.
The chance of them having an affected child is therefore (2/3 chance the woman is a carrier) * (0.0066 chance the man is a carrier) * (1/4 chance that both pass on the recessive allele) = 0.0011, or 0.11%.
Similar Questions
A healthy twenty-seven-year-old female presents to the physician for genetic counseling with her husband. They would like to become pregnant in the near future, but they have concerns that their offspring may develop cystic fibrosis. The wife’s sister has cystic fibrosis, an autosomal recessive disorder with an incidence of approximately 1 in 90,000. The husband’s history is noncontributory.
If both the mother and the father are carriers for the cystic fibrosis gene, what are the chances that their child will be a cystic fibrosis carrier?
If a couple that are both heterozygous carriers of the cystic fibrosis allele have children, the chance that both their first and their second child are carriers is 0.5 x 0.5, or 25%, as determined by theMultiple choice question.
If a healthy young couple are both carriers of cystic fibrosis, the chance that their future child will have this serious illness isMultiple Choice0%.25%.75%.50%.100%.
3. If Sophie conceives a child, and the father neither has cystic fibrosis nor is a carrier, what are the chances that the child would have cystic fibrosis?a. 0%, because the child must receive the bad gene from both parentsb. 50%, because there is a 50% chance that Sophie will pass along the bad genec. 100%, because Sophie has the conditiond. 75%, because Sophie has the condition but the father does note. 25%, because only one in four gametes will carry the bad gene
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