a level biologyWatch
Hence a monohybrid cross essentially involves only one gene (at one locus). For example, if I were to say height is determined by one gene, with dominant T and recessive t alleles, then this would be an example of monohybrid inheritance because only one gene is involved. So any trait that is influenced by a single gene would be a monohybrid cross.
Example: TT x tt
Poly = many
Now normally it's rarely that only one gene would be influencing a particular characteristic. However, when many genes (2 or more) combined together influence a characteristic, it is called a polygenic inheritance.
Let us consider an example where you have three genes that influence height.
Let's assume the first gene has two alleles= A & a
the second gene has two alleles = B &b
and similarly third gene has two alleles = C&c
Now a polygenic inheritance could mean that AABBCC could cross with aabbcc. Since multiple genes (3 in total) are involved, this is an example of polygenic inheirtance.