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Genetic Inheritance Of Cystic Fibrosis

The diagrams below illustrate the potential occurrence of Cystic Fibrosis in children of various combinations of carriers, those that have Cystic Fibrosis and non-carriers.

The chance that a child has CF, is a carrier, or is unaffected is the same for each pregnancy and not influenced by previous pregnancies / children.

Key to Diagrams
eggspermEggs & Sperm
Each will carry on copy of the gene.
White = normal gene
Black = CF variant of gene
key
Outcome Status
Black = Has Cystic Fibrosis: has two copies of the CF gene varaiant
Grey = Carrier: has on copy of CF gene variant and one normal gene
White = NonCarrier: both copies of the gene are normal
Figure 1: Two Carrier Parents
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Two Carrier Parents
Each parent has one copy of the CF gene variant and one normal geneEggs and sperm each carry one copy of either the normal gene or the CF gene variant.For each pregnancy there is:
1 chance in 4 that the child has CF (has two copies of the CF gene variant)
2 chances in 4 that the child is a carrier (has one copy of the CF gene variant)
1 chance in 4 that the child does not have CF nor carry any CF gene variants
Figure 2: CF Parent – NonCarrier Parent
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CF Parent – NonCarrier Parent
CF parent has two copies of CF gene variant, NonCarrier parent has two copies of normal geneEggs and sperm each carry one copy of gene.For each pregnancy :
The child will be a carrier of CF (have one copy of the CF gene variant and one normal gene)
Figure 3: CF Parent – Carrier Parent
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CF Parent – Carrier Parent
CF Parent has two copies of CF gene variant, Carrier parent has one copy of CF gene variantEggs and sperm each carry one copy of gene, in CF parent all genes are CF gene variants, in the Carrier parent one normal copy and one CF gene variantFor each pregnancy there is:
2 chance in 4 the child has CF (has two copies of the CF gene variant)
2 chances in 4 the child is a carrier (has one copy of the CF gene variant)
Fig 4: Carrier Parent – NonCarrier Parent
Carrier parent - non-carrier parentCarrier Parent – NonCarrier Parent
Carrier parent has one copy of CF gene variant, NonCarrier parent has two copies of normal geneEggs and sperm each carry one copy of the gene, in Carrier parent one normal copy and one CF gene variant, in the NonCarrier parent all genes are normalFor each pregnancy there is:
2 chances in 4 the child is a carrier (has one copy of the CF gene variant)
2 chances in 4 the child does not have CF nor carry any CF gene variants