Complementary genes are different
that act together to a
given phenotypical trait.

example, consider a phenotypical
conditioned by 2 complementary
whose alleles are respectively ,
x, Yand y. Performing in
F2 4 different forms are
obtained: X_Y_ ( dominant),
X_yy (dominant for firstpair,
recessive for the ), xxY_
(recessive for the pair, dominant
for the ) and xxyy (double
recessive). is what happens, for
, regarding the colour of
feathers, in which the
dominant interaction results in
feathers, the dominant for first pair,
recessive for second interaction
results in feathers, the recessive
for first pair, dominant for
second interaction leads to feathers
and the double interaction
leads to white .

Each complementary gene segregates
from the others since
are located in different
. Therefore the pattern
follows ’s second law (although it
not obey Mendel’s first ).