suggest reasons for the fact that there are several ways to produce the amino acids that build hemoglobin

Haemoglobin is made up of protein subunits which are termed as globins. The globins are made up of different amino acids which join to form polypeptides. There are more than one type of haemoglobins in humans as there are multiple genes which code for the globins. For example, in humans, the haemoglobin A can be produced by three genes which are HBA1, HBA2, and HBB. Haemoglobin A is the main type of haemoglobin found in humans.

Mutations which occur in the genes which code for haemoglobin causes the variant types of haemoglobin to be formed. However, many of these mutations do not cause any harm or diseases.