What are the expected phenotypic ratios from the following cross:
Tt Rr YY Aa × Tt rr Yy Aa,
where T = tall, t = dwarf, R = round, r = wrinkled, Y = yellow, y = green, A = axial, a = terminal; T, R, Y, and A are dominant alleles. (Note: multiplication method or forked-line method.
Using the multiplication method:
Phenotypic ratio: 9 tall round yellow axial : 3 tall round yellow terminal : 3 dwarf round yellow axial : 1 dwarf round yellow terminal : 9 tall wrinkled yellow axial : 3 tall wrinkled yellow terminal : 3 dwarf wrinkled yellow axial : 1 dwarf wrinkled yellow terminal : 9 tall round green axial : 3 tall round green terminal : 3 dwarf round green axial : 1 dwarf round green terminal : 9 tall wrinkled green axial : 3 tall wrinkled green terminal : 3 dwarf wrinkled green axial : 1 dwarf wrinkled green terminal
Simplified phenotype ratio: 9:3:3:1:9:3:3:1:9:3:3:1:9:3:3:1
Using the forked-line method:
1. Determine the gametes each parent can produce:
- Tt Rr YY Aa can produce gametes TRYA, TRYa, TRYA, TRYa, TrYA, TrYa, TrYA, TrYa (note: each letter represents a different allele)
- Tt rr Yy Aa can produce gametes TrYy, Tryy, tRYA, tRYa, trYA, trYa, trYA, trYa
2. Set up a Punnett square:
| TRYA | TRYa | TRYA | TRYa | TrYA | TrYa | TrYA | TrYa |
Tt Rr | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
YY Aa | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
--------------|---------|-------|-------|----------|-------|-------|---------|
Tt rr | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
Yy Aa | 1 | 1/2 | 1 | 1/2 | 1 | 1/2| 1 | 1/2|
3. Calculate the phenotypic ratio by counting the number of each genotype and phenotype:
Genotypic ratio:
- TTrrYYAA: 1
- TtrryyAA: 1
- ttRrYYAA: 1
- ttRryyAA: 1
- TtrrYYAA: 2
- TtrryyAa: 2
- TtrrYyAA: 2
- TtrryyAA: 2
- TtrrYYAa: 4
- TtrrYyAa: 4
- TtRrYYAA: 2
- TtRryyAA: 2
- TtRrYyAA: 4
- TtRryyAa: 4
- TtRrYYAa: 4
- TtRrYyAa: 4
Phenotypic ratio: 9 tall round yellow axial : 3 tall round yellow terminal : 3 dwarf round yellow axial : 1 dwarf round yellow terminal : 9 tall wrinkled yellow axial : 3 tall wrinkled yellow terminal : 3 dwarf wrinkled yellow axial : 1 dwarf wrinkled yellow terminal : 9 tall round green axial : 3 tall round green terminal : 3 dwarf round green axial : 1 dwarf round green terminal : 9 tall wrinkled green axial : 3 tall wrinkled green terminal : 3 dwarf wrinkled green axial : 1 dwarf wrinkled green terminal