A plant has 4 genes A, B, C and D on chromosome 5. Gene A is very tightly linked to B and gene C is very tightly linked to D. A plant homozygous for alleles A, B, C and D is crossed with another plant homozygous for alleles a, b, c and d. What should be the approximate predicted phenotypic ratio of the F2 population?
1:1:1:1
9:3:3:1
27:9:9:9:3:3:3:1
1:2:2:4:1:2:1:2:1