Genetic Example:
Progeny of a cross between 2 heterozygotes.
Parent #1 Rr X Parent #2 Rr
P(RR) = 1 from each parent =1/2 X 1/2 =1/4
P(rr) = 1 from each parent =1/2 X 1/2 =1/4
P(Rr) = no distinction between parental contribution)
Product rule: R1 X r2 = 1/4 & R2 X r1 = 1/4
Sum rule: 2/4 Rr or 1/2