1. What is the Dihybrid Cross Ratio?

The 9:3:3:1 ratio is the expected phenotypic ratio from a dihybrid cross (cross between heterozygotes for two traits) following Mendel's law of independent assortment. This ratio shows the inheritance pattern of two different traits simultaneously.

2. How Does the Calculator Work?

The calculator compares your observed counts with the expected 9:3:3:1 ratio:

Where:

• 9 — Dominant for both traits
• 3 — Dominant for first trait only
• 3 — Dominant for second trait only
• 1 — Recessive for both traits

Explanation: The calculator normalizes your observed counts to a ratio and calculates deviation from the expected Mendelian ratio.

3. Importance of Dihybrid Cross Analysis

Details: Analyzing dihybrid crosses helps verify whether two genes assort independently (following Mendel's laws) or if they are linked (deviating from expected ratios).

4. Using the Calculator

Tips: Enter counts for each phenotype category. The calculator will show your observed ratio, the expected ratio, and the deviation between them.

5. Frequently Asked Questions (FAQ)

Q1: What does a 9:3:3:1 ratio indicate?
A: It indicates that the two genes are on different chromosomes and assort independently during meiosis.

Q2: What might cause deviation from 9:3:3:1?
A: Possible causes include genetic linkage, incomplete dominance, epistasis, or small sample size.

Q3: How significant does deviation need to be?
A: Use a chi-square test to determine if deviation is statistically significant (p < 0.05).

Q4: Can this ratio appear in test crosses?
A: No, test crosses (with homozygous recessive) would show 1:1:1:1 ratio for independently assorting genes.

Q5: Does this apply to all organisms?
A: The ratio applies to sexually reproducing diploid organisms with independent assortment, but exceptions exist (e.g., linked genes).