What is the best definition of the term compound heterozygous?

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A compound heterozygous condition can be seen in some autosomal-recessive disorders in which two mutated alleles are needed for disease expression. In disorders such as sickle cell disease, both alleles have the identical mutation, which is a homozygous condition. In disorders such as cystic fibrosis and hereditary hemochromatosis, it is possible to have two different mutated alleles contributing to disease expression. A person with this condition is heterozygous for the disease-causing alleles.

What Is the Best Definition of the Term Compound Heterozygous