Kathy's brother has cystic fibrosis. Her husband has no family history of CF. What is the chance that Kathy's child has inherited cystic fibrosis?
Correct answer: D. 2/3 x 1/2 = 1/3
- A. 1/2x 1/2 = 1/4
- B. 1/3 x 1/2 = 1/6
- C. 2/3 x 1/4 = 1/6
- D. 2/3 x 1/2 = 1/3
Explanation
Cystic fibrosis is an autosomal recessive disorder. If Kathy is a carrier, there is a 50% chance she will pass on the CF allele to her child. Therefore, there is a 25% or 1/4 chance that Kathy's child is a carrier of the CF mutation, assuming Kathy's husband does not carry the CF mutation.
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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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