Dental Admissions Test (DAT) 2025 – 400 Free Practice Questions to Pass the Exam

Question: 1 / 400

What is the probability, based on classical Mendelian genetics, of a child being born with cystic fibrosis if one parent is a carrier and the other is homozygous dominant?

0%

25%

When one parent is a carrier for cystic fibrosis (heterozygous) and the other parent is homozygous dominant (no cystic fibrosis allele), the possible genotypes for the offspring will be 50% heterozygous carriers like the first parent and 50% homozygous dominant like the second parent.

Hence, the likelihood of a child being born with cystic fibrosis (homozygous recessive) in this scenario is 0%, making choice A incorrect. Choice C (50%) is incorrect because there is no chance of the child having cystic fibrosis with these parental genotypes. Choice D (100%) is incorrect as it implies that all children would have cystic fibrosis in this scenario, which is not possible based on Mendelian genetics. Thus, the correct answer is B (25%) because there is a 25% chance of the child being a carrier for cystic fibrosis.

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50%

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