Genetic Transmission

We Are all « build up » with chromosomes transmitted by our parents.

Half of them come from our mother, the other half come from our father. We have 23 pairs of chromosome. The genes are “written” on the chromosomes. Each genetic disorder is due to one (or more) defective gene(s). There are 2 ways of transmitting the defective gene : Autosomal dominant et Autosomal recessive. For each pregnancy the risks of transmission are the same.

Autosomal Dominant : Only one defective gene is sufficient for the disorder to express itself (to be shown).

Father (or mother)                            Mother  (or father)


One of the two parents  suffers from an autosomal dominant disorder. One out of the two chromosomes has the defective gene. His body “shows” the disorder, it is expressed. There 1 risk out of 2, for each pregnancy, for transmitting the child the genetic default, and having  a child who, him(her)self ,is expressing the disorder.

Autosomal Recessive.  The 2 chromosomes must have the defective gene for the disorder to express itself. If only one chromosome has it,  one is  just « carrier » of the disorder, but it  isn’t expressed.

  1. A)The two parents are “ carriers”

Father (or mother)                            Mother (or father)


the risks are the same :

–         1 risk out of 2 for the child to be carrier

–         1 chance out of 4 for the child to have nothing at all.

–         1 risk out of 4 for for the child to express the disorder

(  If only one of the 2 parents is carrier, there is no risk for having a child expressing the disorder and 1 risk out of 2 for the child to be « carrier » )

  1. B) One of the 2 parents expresses the disorder

Father (or mother)                              Mother (or father)


All the children will be carriers.