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Answer: 2. Each subunit represents a separate polypeptide chain, while one polypeptide chain may contain several domains.
Explanation: Each subunit constitutes of one polypeptide chain. A polypeptide chain has one particular gene coding for it. thus it simply implies that a protein must have one gene for each subunit.
Many proteins is made up of different protein domains. A particular domain may appear in a variety of different proteins.
domains are stable on there own, they can be exchanged via genetic engineering between one protein and another.
I believe that hair and limbs are homology because all mammals have hair and similar limb structure. Hair loss and social behavior on the other hand are homolasy because not all mammals have them. Homology is the similar traits due to common ancestry while homoplasy is similar traits for other reasons other than common ancestry.
