How many of the given statements are correct regarding the inheritance of human skin colour? 1. It is an example of polygenic inheritance. 2. It is controlled by three genes. 3. The phenotype is determined by the cumulative effect of genes. 4. The intensity of skin colour is determined by the amount of melanin. 5. Environmental factors like sunlight do not affect skin colour. 6. The inheritance pattern shows distinct classes, not a continuous variation.