Cystic fibrosis is a lethal, autosomal recessive genetic disorder. Which statement BEST explains how cystic fibrosis is maintained in the gene pool? A Organisms that are heterozygous can pass on only the dominant allele. B Organisms that are homozygous-dominant pass on either dominant or recessive alleles. C Organisms that are heterozygous can pass on either dominant or recessive alleles. D Organisms that are homozygous-recessive pass on only the dominant allele.

The right answer is : A Organisms that are heterozygous can pass on only the dominant allele.

Cystic fibrosis is a genetic disorder affecting the glandular epithelia of many organs. It is the most common lethal genetic disease with autosomal recessive inheritance in Europoid type populations, whereas it is very rare in African and Asian populations.

For a heterozygous subject, he has a recessive allele (the mutated allele) and a dominant allele (normal). In this subject the disease is not expressed as it is recessive compared to the normal allele, therefore, only the dominant allele will be expressed in subjects heterozygote for cystic fibrosis.