The reason why roosters develop a bigger comb than hens could rely on the fact of gene expression. Although an organism has the same charge of DNA along all its cells, not all these traits stored in the DNA are expressed. This also happens between the two genders of a particular species, like us, the human being, and the differences between men and women, for example, the development of different genitalia. In the case of roosters and hens, both develops different traits due to the action of