Bob and Brenda are both heterozygous for a genetically inherited recessive trait. (a) Calculate the probability that they would have a healthy child. Use a genetic diagram to help. (b) Suggest an example of a recessive inherited disorder

Heterozygous means that the parents both carry a dominant allele (A) and a recessive allele (a).

Dominant alleles are always expressed in the phenotype. Recessive alleles are expressed in the phenotype only if two recessive (a) alleles are present (one from the mother and one from the father).

For recessive disorders:

If a child inherits one dominant (A) allele and one recessive (a) allele, they are carrier for a recessive disorder.

If a child inherits two recessive (a) alleles, they will have the disease.

A             a

A             AA          Aa

a              Aa           aa

a) Probability of a healthy child= ¼ or 25%

b) Example of a recessive trait= Cystic Fibrosis/ Sickle-Cell disease/Tay-Sachs disease