Phenotypic Ratio Calculator Dihybrid Cross Lab

Dihybrid Cross:

\[ \text{Expected Ratio} = 9:3:3:1 \]

Dominant for both traits (Phenotype 1):

count

Dominant trait A, Recessive trait B (Phenotype 2):

count

Recessive trait A, Dominant trait B (Phenotype 3):

count

Recessive for both traits (Phenotype 4):

count

Observed Phenotypic Ratio:

Chi-Square Value:

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1. What is a Dihybrid Cross?

A dihybrid cross is a breeding experiment between two organisms that are identically hybrid for two traits. It follows Mendel's principle of independent assortment and typically results in a 9:3:3:1 phenotypic ratio in the F2 generation.

2. How Does the Calculator Work?

The calculator uses the chi-square test to compare observed and expected ratios:

\[ \chi^2 = \sum \frac{(O - E)^2}{E} \]

Where:

\( O \) — Observed count for each phenotype
\( E \) — Expected count based on 9:3:3:1 ratio
\( \sum \) — Sum of all four phenotype calculations

Explanation: The chi-square test determines whether the observed data significantly deviates from the expected 9:3:3:1 ratio.

3. Importance of Phenotypic Ratio Calculation

Details: Calculating phenotypic ratios helps verify Mendelian inheritance patterns, test genetic hypotheses, and determine if traits are independently assorting or linked.

4. Using the Calculator

Tips: Enter the observed counts for each of the four phenotypes from your dihybrid cross experiment. All values must be non-negative integers.

5. Frequently Asked Questions (FAQ)

Q1: What does a 9:3:3:1 ratio represent?
A: This ratio represents the expected phenotypic distribution in a dihybrid cross: 9/16 dominant for both traits, 3/16 dominant A/recessive B, 3/16 recessive A/dominant B, and 1/16 recessive for both traits.

Q2: How do I interpret the chi-square value?
A: Compare your calculated chi-square value to critical values from a chi-square distribution table with 3 degrees of freedom. A p-value > 0.05 suggests the observed ratio doesn't significantly differ from expected.

Q3: What if my ratio significantly deviates from 9:3:3:1?
A: Significant deviation may indicate gene linkage, epistasis, lethal alleles, or errors in experimental procedure.

Q4: What sample size is recommended?
A: Larger sample sizes (100+) provide more reliable results. Small samples may not accurately represent the expected ratio.

Q5: Can this calculator be used for trihybrid crosses?
A: No, this calculator is specifically designed for dihybrid crosses with their characteristic 9:3:3:1 ratio.