Problem Analysis:
The task involves solving a dihybrid cross problem using Mendelian genetics. The goal is to:
1. List the gametes produced by the given parents.
2. Complete a Punnett square for a dihybrid cross.
3. Determine the phenotype ratio of the offspring.
####
Step 1: Understand the Genotypes and Phenotypes
-
Parent 1: Green and wrinkly seed (ggww)
- Genotype: ggww
- Phenotype: green (recessive) and wrinkly (recessive)
-
Parent 2: Heterozygous yellow and round seed (YyWw)
- Genotype: YyWw
- Phenotype: yellow (dominant) and round (dominant)
####
Step 2: List the Gametes
To solve this, we need to determine the gametes produced by each parent.
-
Parent 1 (ggww):
- Since both alleles are recessive and homozygous, the only possible gamete is:
-
gw
-
Parent 2 (YyWw):
- This parent is heterozygous for both traits. Using the law of independent assortment, the possible gametes are:
-
RY,
Ry,
rY,
ry
####
Step 3: Complete the Punnett Square
We are tasked with completing a Punnett square for a cross between two heterozygous parents (YyWw × YyWw). The gametes for both parents are:
- Parent 1 (YyWw): RY, Ry, rY, ry
- Parent 2 (YyWw): RY, Ry, rY, ry
The Punnett square will have 16 boxes (4 × 4).
####
Step 4: Fill in the Punnett Square
We combine the gametes from each parent to fill in the Punnett square:
| | RY | Ry | rY | ry |
|-------|--------|--------|--------|--------|
|
RY| RRYy | RRYy | RrYy | RrYy |
|
Ry| RRYy | RRYy | RrYy | RrYy |
|
rY| RrYy | RrYy | rrYy | rrYy |
|
ry| RrYy | RrYy | rrYy | rrYy |
####
Step 5: Determine the Phenotypes
Using the key provided:
-
R = Round (dominant)
-
r = Wrinkly (recessive)
-
Y = Yellow (dominant)
-
y = Green (recessive)
Now, let's classify each genotype into its corresponding phenotype:
1.
Round & Yellow: Genotypes with at least one
R and one
Y (e.g., RRYy, RrYy).
2.
Round & Green: Genotypes with at least one
R but no
Y (e.g., RRyy, Rryy).
3.
Wrinkly & Yellow: Genotypes with at least one
Y but no
R (e.g., rrYy).
4.
Wrinkly & Green: Genotypes with neither
R nor
Y (e.g., rryy).
From the Punnett square:
-
Round & Yellow: RRYy, RRYy, RRYy, RRYy, RrYy, RrYy, RrYy, RrYy (8 total)
-
Round & Green: RRyy, RRyy, Rryy, Rryy (4 total)
-
Wrinkly & Yellow: rrYy, rrYy, rrYy, rrYy (4 total)
-
Wrinkly & Green: rryy, rryy, rryy, rryy (4 total)
####
Step 6: Calculate the Phenotype Ratio
Count the number of each phenotype:
- Round & Yellow: 9
- Round & Green: 3
- Wrinkly & Yellow: 3
- Wrinkly & Green: 1
The phenotype ratio is:
\[
\boxed{9:3:3:1}
\]
Final Answer:
\[
\boxed{9:3:3:1}
\]
Parent Tip: Review the logic above to help your child master the concept of dihybrid punnett square worksheet.
