* Genes: The shape of your hair follicles is determined by your genes. Round or oval follicles tend to produce straight hair, while oval or flat follicles tend to produce curly or wavy hair. There isn't one specific "curly hair gene," but rather a combination of genes that influence hair texture.
* Hair Follicle Shape: If the hair follicle is asymmetrical (e.g., oval or flat), the hair grows out in a curved shape, leading to curls or waves. The more asymmetrical the follicle, the tighter the curl.
* Keratin Distribution: Keratin is the main protein that makes up hair. In curly hair, the keratin is distributed unevenly along the hair shaft. This uneven distribution causes the hair to bend and curl.
* Ethnicity: Certain ethnicities are more prone to having genes that result in curly hair. However, curly hair can occur in people of any ethnic background.
In summary, a boy gets curly hair because he inherited genes that result in asymmetrical hair follicles and an uneven distribution of keratin in the hair shaft.