Question

Can you fill the dihybrid cross given in the problem and find the phenotype ratio?

Answer 1

I can — but I need the specific cross from your problem (parent genotypes and which alleles are dominant). If you don’t have those details, here is the standard worked example and method you can apply.

Example: Parents = AaBb × AaBb (independent assortment, complete dominance: A > a, B > b).

1) Write the possible gametes from each parent:
- Each parent can produce: AB, Ab, aB, ab (each with probability 1/4).

2) Make a 4×4 Punnett square with those gametes for rows and columns and fill each cell by combining gametes:
Row/column order AB, Ab, aB, ab.

Filled cells:
- AB×AB = AABB
- AB×Ab = AABb
- AB×aB = AaBB
- AB×ab = AaBb
- Ab×AB = AABb
- Ab×Ab = AAbb
- Ab×aB = AaBb
- Ab×ab = Aabb
- aB×AB = AaBB
- aB×Ab = AaBb
- aB×aB = aaBB
- aB×ab = aaBb
- ab×AB = AaBb
- ab×Ab = Aabb
- ab×aB = aaBb
- ab×ab = aabb

3) Count phenotypes (dominant allele presence):
- A_ B_ (both dominant phenotypes): 9 cells
- A_ bb (A dominant, B recessive): 3 cells
- aa B_ (A recessive, B dominant): 3 cells
- aa bb (both recessive): 1 cell

Phenotype ratio = 9 : 3 : 3 : 1.

(Genotype ratio if you want it: 1 AABB : 2 AABb : 1 AAbb : 2 AaBB : 4 AaBb : 2 Aabb : 1 aaBB : 2 aaBb : 1 aabb.)

If your problem uses different parental genotypes (e.g., AaBb × aabb, or AABB × aabb), or different dominance, tell me the exact cross and I’ll fill the specific square and give the phenotype ratio.