The Genetic Inheritance of Cystic Fibrosis
The diagrams below illustrate the potential occurrence of Cystic Fibrosis in children of various combinations of carriers, 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
 | Eggs and Sperm Each will carry one copy of the gene. White = normal gene Black = CF variant of gene |  | Outcome Status Black = Has Cystic Fibrosis: has two copies of CF gene variant Grey = Carrier: has one copy of CF genevariant and one normal gene White = NonCarrier: both copies of the gene are normal |
Figure: 1
 |
Two Carrier Parents each has one copy of the CF gene variant
Eggs and sperm carry one copy each, 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 |
| Has CF Carriers No CF |
Figure: 2
 | CF Parent - NonCarrier Parent CF parent has two copies of the CF gene variant, NonCarrier Parent has two copies of normal gene
Eggs and sperm carry one copy of gene, in CF parent all genes are CF gene variants, in the NonCarrier Parent all genes are normal
For each preganancy: The child will be a carrier of CF (have one copy of the CF gene variant and one normal gene) |
All Carriers |
Figure: 3
 |
CF Parent - Carrier Parent CF parent has two copies of CF gene variant, Carrier parent has one copy of CF gene variant
Eggs and sperm 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 variant
For each pregnancy there is: 2 chances 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) |
| Has CF Carrier Has CF Carrier |
Figure: 4
 |
Carrier Parent - NonCarrier Parnt Carrier parent has one copy of CF gene variant, NonCarrier Parent has two copies of normal gene
Eggs and sperm carry one copy of gene, in the Carrier Parent one normal copy and one CF gene variant, in the NonCarrier Parent all genes are normal
For 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 |
| Carriers No CF |
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