Question

In which generation is a recessive deleterious allele most likely to negatively affect the fitness of the individual expressing it?

Answer 1

The generation when dominant deleterious alleles are expressed. It is the time when the negative effect comes out and affect the fitness of an individual. If an individual only carries one recessive deleterious allele it would have a different effect and would stay healthy. However, the next generation from this individual would inherit the deleterious alleles and have the said negative effect.