The polled gene is luckily one of cattle breeding simpler genes to understand; it is a single gene so the inheritability is straight forward.   A a rule genes come in pairs, and fortunately the polled is dominant to the horned gene.

A polled animal that has two copies of the polled gene is know as homozygous polled and this animal mated to horned animals will produce 100% polled calves.  These calves will have inherited a copy of the polled gene and a copy of the horned gene from each parent.  These polled animals that carry the horned gene are called heterozygous polled.

Homozygous polled is often indicated as PP, so can only pass on the dominant polled gene.

Heterozygous polled is often indicated as Pp the small p indicates the horned gene. This animal will pass on either (randomly) a polled gene or a horned gene two its progeny. So mated to horned animal you will expect 50% polled and 50% horned.

For a more detailed explanation Signet have the following useful article...... click here