The ability to curl one's tongue into a u-shape is a genetic trait. curlers always have at least one curler parent but noncurlers can have one or both parents who are curlers. using c and c to symbolize the alleles that control this trait, what is the genotype of a noncurler?

A noncurler has a genotype cc.

Explanation:

If curlers always have at least one curler parent, it is possible being "curler" will be related to a dominant allele, in this example, "C".  So, being "noncurler" could be a recessive trait. Noncurler can have one or both parents who are curlers, and this is concordant with a recessive inheritance if both parents are heterozygous (Cc) (with a probability of 25% of being "noncurler"). Also, it is possible if one parent is heterozygous and the other is homozygous for c (Cc x cc), this with a probability of 50% ob being "noncurler".  

The Punnett square shows this clearly.

the correct answer is primary!