"The Barred Plymouth Rock breed carries a gene for barring (B) that is carried on the Z chromosome (see Figure 2). This gene produces a white bar on an otherwise black feather. The gene is incompletely dominant over the non-barring gene (b). In adults, the male, with two barring genes (BB), has feathers with broader white bars than those of the female, who has only one of the barring genes (B_). As a result, males are overall lighter in color. The sex of purebred Barred Plymouth Rocks chicks can be determined on the basis of the size and shape of a light-colored spot on the top of the head. At hatch, males have a large white spot. The spot is much smaller and narrower in females. This has been found to be about 80% accurate."
and their legs are darker as opposed to yellow and big.
