A child with cystic fibrosis (CF) asks the nurse why he has this disease, but his parents are perfectly healthy. The nurse explains:
A) Environmental conditions affect on alleles and therefore who get CF
B) Both parents are carriers and have a recessive genotype with alleles for CF.
C) One of your parents may have a mild recessive form of CF.
D) Both parents have homozygous pairing of two alleles for CF.
Ans: B
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Both multifactorial inheritance and polygenic inheritance involve multiple genes at different loci. Multifactorial is different because it involves the effects of the environment on genes also. Unlike Mendel law, multifactorial inheritance and polygenic inheritance are unpredictable. Homozygous pairing of alleles is characteristic of recessive traits. The gene for the genetic disorder cystic fibrosis is recessive. Therefore, only persons with a genotype having two alleles for cystic fibrosis have the disease. In most cases, neither parent manifests the disease; however, both must be carriers.
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