Answer:
This is most likely due to a mutation in a maternal effect gene.
Explanation:
The genes of maternal effect are the result of a special genetic inheritance that is managed by genes present only in the mother's body, of a certain individual. These genes are responsible for determining some specific conditions in the egg, generating some changes in the individual's genotype and phenotype. In summary, these genes are responsible for contributing to the phenotype of an individual directly related to the mother's genotype.
Like any gene, genes of maternal effect can mutate, generating some phenotypic anomalies. An example of this is the existence of two tails in an abnormal embryo of Drosophila.
