If a person is heterozygous for a recessive disease allele, how much normal protein do they usually produce?

When a person is heterozygous for a recessive disease allele, they possess one normal allele and one recessive allele for the gene in question. The normal allele typically produces functional protein, while the recessive allele, which is often non-functional or has reduced function, does not contribute effectively to protein production.

In this scenario, because alleles can be thought of in terms of their contributions to protein production, the normal allele would allow for the production of protein at approximately 100% capacity. However, since the heterozygous individual has one normal allele and one recessive allele, it is reasonable to conclude that the functional contribution from the normal allele may lead to the production of about 50% of the total protein output compared to an individual who is homozygous for the normal allele.

This supports the idea that having one normal allele can produce enough protein to functionally compensate for the recessive allele, making it likely that a heterozygous person will produce around 50% of the normal protein output associated with the typical functionality of that gene. This understanding aligns with basic Mendelian principles, where the presence of a dominant normal allele often results in enough functional protein to avert any phenotype associated with the recessive allele.