Question

for the following problem please provide me a key for allele symbols, the genotype for each parent, a punnett square with the male and female symbols, and answers to the questions.
in fruit flies, dumpy wings are shorter and broader than normal wings. the allele for normal wings (D) is dominant to the allele for dumpy wings (d). two normal winged flies were mated and produced 300 normal wined and 100 dumpy winged flies. what are the likely genotypes of the parents?

Answer 1

Allele key
- D = allele for normal wings (dominant)
- d = allele for dumpy wings (recessive)

Likely parental genotypes
- Parent (male): Dd
- Parent (female): Dd

Reason: The offspring ratio is 300 normal : 100 dumpy = 3 : 1, which is the classic phenotypic ratio from a heterozygote × heterozygote (Dd × Dd) cross.

Punnett square (female on left, male on top)
♂ D d
♀ D | DD | Dd |
d | Dd | dd |

Genotypes in boxes: DD, Dd, Dd, dd
Phenotypes: DD = normal, Dd = normal (carrier), dd = dumpy

Expected ratios and numbers (from Dd × Dd)
- Genotype ratio: 1 DD : 2 Dd : 1 dd
- Phenotype ratio: 3 normal : 1 dumpy
- For 400 offspring: 300 normal (100 DD + 200 Dd) and 100 dumpy (100 dd)

Why other parental genotype combinations are unlikely
- DD × DD or DD × Dd would give all normal offspring (no dumpy) — not consistent with 100 dumpy.
- dd × Dd would give a 1:1 normal:dumpy ratio (≈200:200) — not consistent with 300:100.
- dd × dd would give all dumpy — not consistent.

Conclusion: Both parents were most likely heterozygous (Dd).