A researcher believes that she had found the gene that determines weight in mice. However, when she removes this gene from all of the cells in an animal, she observes that there is no difference between its weight and that of untreated mice. Furthermore, she can observe no other atypical phenotypes in the subject mouse. How can this be explained?

Weight in mice is influenced by multiple alleles of the same gene.

Weight in mice is a polygenic trait.

Only the recessive allele of the gene determines an animal's weight.

The gene removed from the animal is pleiotropic.