Combine the given two facts to write a concluding fact. Note that there should be some parts of the first and second facts that are not mentioned in this conclusion fact. Your combined fact should be the result of a chain between the two facts. Chains form when two facts connect together to produce a concluding fact. An example of a chain is: "pesticides cause pollution" (fact1) + "pollution can harm animals" (fact2) → "pesticides can harm animals" (conclusion fact). Parts of the concluding fact overlap with the first and the second fact. To construct such a  concluding fact, a useful way is to borrow the subject from one fact and the ending conclusions from another fact.

Fact 1: Introns are regions that do not code for proteins. 
Fact 2: Introns are found in eukaryotes.
eukaryotes have regions that do not code for proteins.

Fact 1: Any antigen that causes an allergy is called an allergen. 
Fact 2: Asthma attacks are caused by allergies.
Allergens can trigger asthma attacks.

Fact 1: Skin color is another polygenic trait. 
Fact 2: Phenotypic expression of polygenic traits varies over a wide range.

Phenotypic expression of skin color varies over a wide range.