1. An unaffected couple has a daughter affected with Koopski\'s disease. Which t
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Question
1. An unaffected couple has a daughter affected with Koopski's disease. Which type(s) of inheritance can be ruled out for Koopski's disease? (Choose all that are correct)
a. Autosomal dominant
b. X-linked dominant
c. Autosomal recessive
d. X-linked recessive
2. A man affected with the autosomal recessive disorder cystic fibrosis (CF) mates with a normal woman. Which of the following statements about the transmission of CF to his kids is TRUE? (Choose all that are correct)
a. All of his sons will be affected
b. All of his sons will be carriers
c. All of his daughters will be affected
d. All of his daughters will be carriers
Explanation / Answer
The couples are unaffected which means that they do not have disease. Their daughter is affected.
1. If the disease is autosomal dominant, any or both of the parents either with homozygous or heterozygous dominant alleles have to be affected. But, the parents are not affected in this case. So, the parents must be homozygous recessive in which case, even the daughter must not be having the gene. But, it is given that daughter is affected. So, this option is false.
If the disease is autosomal recessive, any or both the parents have to be affected when homozygous recessive alleles are present. As the parents are unaffected, they must be homozygous dominant or heterozygous recessive. If the parents are homozygous dominant, the daughter will not get affected gene. So, they must be heterozygous recessive in which case the parents are carriers of the gene and are not affected. If the parents are heterozygous recessive, 25% of the off springs are affected and the remaining is unaffected. So, the daughters might fall in that sector. Therefore, autosomal recessive option is true.
If the disease is X-linked dominant, both the parents would have been affected. But, they are not. All the children will be affected including sons and daughters in this case, which is not correct. Only daughter is affected. So, this option is false.
If the disease is X-linked recessive, one of the parents must be affected. But, it is not the case. So, this option is false.
2. Here, if normal woman is considered to be not a carrier, she must be homozygous dominant.
male-cc X female-CC
Offspring - Cc Cc | Cc Cc
All are carriers. The options b and d are true.
If the normal woman is heterozygous recessive or a carrier, then 50% offspring are carriers and 50% are affected.
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