How do 2 people without sickle-cell anemia to have a child with sickle-cell disease?

Yes: The defect of sickle cell anemia occurs when 2 sickle cell genes are passed to a newborn. Since each parent passes half their genes at conception & it takes 2 sickle genes to cause disease, one gene comes from each parent. Many parents carry this gene quietly, unknown to them because it doesn't make a single gene carrier sick.

It's required: A child with sickle cell disease inherited a sickle gene from both parents, therefore both parents must carry the gene. Millions of people in the world have sickle cell trait (they carry one normal gene and one sickle gene). They are generally healthy. But, if two of them have children together each child has a 25% chance of inheriting sickle cell disease by inheriting the sickle gene from both.

Each carries S Trait: Recessive disorders are so named because they are not expressed unless two genes of the same type are carried in the chromasomes. Dominedt genes can show up when only one gene is present. Sickle cell requires 2 recessive genes, one from each unaffected parent. Prenatal testing and genetic counseling are encouraged for populations at risk.

Parents have trait: One biological parent would need to have sickle cell trait and the other biological parent would need to have sickle cell trait/ hemoglobin c trait/ or a form of beta thalassemia trait - depending upon the type of sickle cell disease.

Genetics: Sickle cell disease must be inherited from both parents. Sickle cell trait (1 sickle gene, 1 normal gene) is usually asymptomatic. 2 persons with sickle cell trait have a 1/4 chance of having a child with sickle cell disease, but the parents are often unaware that they have anything.