<h2>Maternal effect</h2>
Explanation:
In maternal effect the phenotype of the progeny is decided by the genotype of the mother
- The female partner is one step ahead to her male partner
- The ovum transcribes some of its nuclear genes prior to fertilization and these genes are responsible for the development of embryo that is why these genes are called maternal effect genes
- This effect is observed in Drosophila
In the given question both male and female have brown eyes with Nn genotype,phenotype of the offspring will be decided by the genotype of mother(Nn) hence despite of having recessive genotype(nn) all the offsprings will show brown eyes