After reading the Learn.Genetics Observable Human Characteristics article, it should be clear that many observable human features are controlled by multiple genes, as well as being influenced by environmental factors. However, from the list given in the reading, which of the following trait(s) appear to be controlled by a single gene and entirely genetically based/inherited? (i.e., without environmental factors). Select a l that apply.
a. Freckles
b. Hand clasping
c. Red/green colorblindess
d. PTC tasting
e. curly hair
f. tongue rolling