How many gentypic classes are expected from a tetrahybrid (4-gene) cross?

Answer 1

Sixteen.

Answer 2

let n = the number of heterozygous gene pairs
2 to the nth power = the number of different types of gametes produced
2 to the 2n = possible genotypes however


Tetrahybrid has:
(P+q)^8 = 2^8 = 2^2n = 256 different progeny
1:8:28:56:70:56:28:8:1 genotype ratio distribution
81:27:27:27:27:9:9:9:9:9:9:3:3:3:3:1 phenotypes