Below are some of the crosses of fish that were mated to produce sighted offspring in a single generation. The fish (true-breeding) were taken from caves and mated to true-breeding fish from caves in different locations. You know that blindness is controlled by multiple genes and inherited in a recessive fashion.

Based on these results, at least how many genes are working to produce sight?

Cave 1 Fish Cave 2 Fish Cave 3 Fish Cave 4 Fish Cave 5 Fish
Cave 1 Fish Blind Blind Sighted Sighted Sighted
Cave 2 Fish Blind Blind Sighted Sighted Sighted
Cave 3 Fish Sighted Sighted Blind Sighted Blind
Cave 4 Fish Sighted Sighted Sighted Blind Sighted
Cave 5 Fish Sighted Sighted Blind Sighted Blind

a) 1 b) 2 c) 0 d) 4 e) 5