Answer:
The six finger allele
Step-by-step explanation:
In this case, the six finger allele is dominant because, the allele was the trait later observed in the individual's phenotype. A dominant allele is one of a pair of alternative forms of a gene that controls the character of which the code codes for and also mask the effect of the alternative form.
Thus, since the six finger allele was expressed masking the effect of the five fingered allele, it is thus the dominant allele.