Answer:
Polygene
Step-by-step explanation:
Continuous variation occurs because of the effect of the combination of many genes (polygenes) which and is called polygenic inheritance. So in polygenic inheritance, each gene or trait contributes to the character. In discontinuous variation mainly alleles of a single gene are involved.
Polygenic trait inheritance can be influenced by the environment for example in cows the milk yield is not only affected by genes but also by environmental factors like weather, diet, etc. Some other examples of continuous variation are height, weight, shoe size, etc.
So polygenes are involved in determining multiple factor traits or continuous variation.