Cystic fibrosis is a recessive genetic disorder caused by a mutation of the CTRF gene. The disease is characterized by excessive mucus production along the respiratory and digestive tracts in addition to other symptoms. Cystic fibrosis is a progressive disorder that is most associated with chronic respiratory disease.

Sara and Anthony found out that they are both carriers of the disorder, but neither have the disease. What are the chances their child will be born with cystic fibrosis?
A.
0:4
B.
1:2
C.
4:4
D.
1:4

Since both Anthony and Sara are healthy carriers of the gene that causes cystic fibrosis, the chance of having a child with this disease are 1:4 (option D).

Explanation:

The inheritance pattern of cystic fibrosis is autosomal recessive, and considering that both parents carry the abnormal CFTR gene, it can be said that the parental genotypes are:

Anthony N/Qf

Sara N/Qf

Where N is the normal gene and Qf is the abnormal gene.

Since this is an autosomal recessive disorder, only the homozygosity of the defective allele will cause the disease to manifest :

N/Qf X N/Qf

Alleles     N       Qf

N            N/N    N/Qf

Qf           N/Qf  Qf/Qf

Therefore, the chance of Anthony and Sara having a child with cystic fibrosis is 1:4.

Learn more:

Cystic fibrosis inheritance link

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