The traits which are controlled by more than one gene are known as:

Polygenic traits

The correct answer is Option (1) → Polygenic traits

Polygenic inheritance involves the influence of multiple genes on a single phenotypic trait. Polygenic inheritance is an inheritance pattern controlled by three or more genes (multiple genes) and the graded phenotypes are due to the additive or cumulative effect of all the different genes of the trait. An example of human skin colour to understand the phenomenon of polygenic inheritance.

In a polygenic trait the phenotype reflects the contribution of each allele, i.e., the effect of each allele is additive. To understand this better let us assume that three genes A, B, C control skin colour in human with the dominant forms A, B and C responsible for dark skin colour and the recessive forms a, b and c for light skin colour. The genotype with all the dominant alleles (AABBCC) will have the darkest skin colour and that with all the recessive alleles (aabbcc) will have the lightest skin colour. As expected the genotype with three dominant alleles and three recessive alleles will have an intermediate skin colour. In this
manner the number of each type of alleles in the genotype would determine the darkness or lightness of the skin in an individual.