Keratins cysteine determination

The a-keratin of hair is rich in the amino acid cysteine. The location of these cysteines in the protein chain is genetically determined as a result of the location of the cysteines in the protein, a person may have curly, wavy, or straight hair. How can the location of cysteines in a-keratin result in these different styles of hair Propose a hypothesis to explain how a "perm" causes straight hair to become curly. 

Alpha keratin is found in sheep wool. The springy nature of wool is based on its composition of alpha helices that are coiled around and cross-linked to each other through cystine residues. Chemical reduction of the cystine in keratin to form cysteines breaks the cross-links. Subsequent oxidation of the cysteines allows new cross-links to form. This simple chemical reaction sequence is used in beauty shops and home permanent products to restructure the curl of human hair—the reducing agent accounts for the characteristic odor of these products. Beta keratin is found in bird feathers and human fingernails. The more brittle, flat structure of these body parts is determined by beta keratin being composed of beta sheets almost exclusively. 

Like feathers and hair, wool consists mainly of keratin. This polypeptide contains L-cystine which is the oxidised (disulfide) form of L-cysteine. The former acts as a cross-link which determines the crimped nature of wool. In human hair this process is, of course, carried out reversibly in permanent waving ... 

---