of the American Simmental Association
polled trait depends on just one gene, expressed
by the symbol “P”. The opposite
condition, the presence of horns, is expressed
as the “p” gene.
polled gene (P) is dominant to the horned gene
(p). When an animal inherits the dominant P
gene from one parent, it is the dominant P that
shows up in the individual’s appearance
as the polled trait. The only time the recessive
horn gene (p) can express itself is when the
dominant P gene is not present.
are three possible gene combinations involving
the polled trait. They are PP, Pp, and pp. Half
of each combination is inherited form each parent.
PP individual is polled and said to be homozygous
because it possesses two identical genes (“homo”
means “the same”). It will have
all polled offspring regardless of whether the
other parent is horned or polled, because it
has only the dominant P gene to pass on to its
progeny. PP bulls are sometimes referred to
as 100% dehorners.
Pp individual is also polled, but is heterozygous
(“hetero” means “not the same”).
The Pp individual passes two different genes,
so it won’t breed true for the polled
trait. Fifty percent of the time, the Pp individual
will pass on the horn gene, p, to its progeny.
pp individual is horned, and is also homozygous
because it has two identical genes. The pp individual
will always pass on the p (horned) gene to its
progeny, because that’s all it possesses.
in mind that each parent passes one-half of
its genetic makeup to its offspring.