Number of kinds of phenotypes in `F_(2)` generation of mendel's dihybrid cross

Options

A. 5
B. 6
C. 8
D. 4

Answer

To determine the number of kinds of phenotypes in the F2 generation of Mendel's dihybrid cross, we can follow these steps:

### Step 1: Understand the Dihybrid Cross
A dihybrid cross involves two traits, each represented by two alleles. For example, in Mendel's experiments, he used seed color (yellow vs. green) and seed shape (round vs. wrinkled). The dominant traits are yellow (Y) and round (R), while the recessive traits are green (y) and wrinkled (r).

**Hint:** Remember that a dihybrid cross involves two different traits, each with two alleles.

### Step 2: Identify the Parental Genotypes
In Mendel's dihybrid cross, the parental genotypes were:
- One parent: Homozygous dominant for both traits (YYRR)
- Other parent: Homozygous recessive for both traits (yyrr)

**Hint:** Identify the dominant and recessive traits to understand the parental genotypes.

### Step 3: Determine the F1 Generation
When these two parents are crossed, all offspring in the F1 generation will be heterozygous for both traits (YyRr). This means they will express the dominant phenotypes: yellow and round.

**Hint:** The F1 generation will show the dominant traits due to the presence of dominant alleles.

### Step 4: Perform Selfing of the F1 Generation
To obtain the F2 generation, the F1 individuals (YyRr) are self-fertilized. The gametes produced by the F1 generation can be:
- YR
- Yr
- yR
- yr

**Hint:** Use a Punnett square to visualize the combinations of gametes from the F1 generation.

### Step 5: Construct the Punnett Square
By setting up a Punnett square with the gametes from the F1 generation, we can determine the phenotypic ratios of the offspring in the F2 generation.

**Hint:** Each cell in the Punnett square will represent a possible genotype for the offspring.

### Step 6: Analyze the F2 Generation Results
The resulting phenotypes from the Punnett square will be:
1. Yellow Round (YYRR, YYRr, YyRR, YyRr) - 9
2. Yellow Wrinkled (YYrr, Yyrr) - 3
3. Green Round (yyRR, yyRr) - 3
4. Green Wrinkled (yyrr) - 1

This gives a phenotypic ratio of 9:3:3:1.

**Hint:** Count the number of different phenotypes represented in the results.

### Step 7: Conclusion
From the analysis, we find that there are **four distinct phenotypes** in the F2 generation: yellow round, yellow wrinkled, green round, and green wrinkled.

**Final Answer:** The number of kinds of phenotypes in the F2 generation of Mendel's dihybrid cross is **4**.

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