1. What is the Dihybrid Cross Ratio?

The 9:3:3:1 ratio is the expected phenotypic ratio of a dihybrid cross (cross between two heterozygous individuals for two traits) following Mendelian inheritance patterns. This ratio demonstrates the principle of independent assortment.

2. How Does the Calculator Work?

The calculator uses the classic dihybrid cross ratio:

Where:

• 9 — Dominant for both traits
• 3 — Dominant for first trait, recessive for second
• 3 — Recessive for first trait, dominant for second
• 1 — Recessive for both traits

Explanation: The calculator also computes expected counts based on your total offspring number and calculates a chi-square value to test how well your observed data fits the expected ratio.

3. Importance of Dihybrid Cross

Details: Understanding dihybrid crosses is fundamental in genetics, demonstrating how different traits are inherited independently when their genes are located on different chromosomes.

4. Using the Calculator

Tips: Enter your observed phenotype counts and total offspring number. The calculator will show the expected ratio, expected counts, and chi-square value to assess goodness of fit.

5. Frequently Asked Questions (FAQ)

Q1: Why is the ratio 9:3:3:1?
A: It results from the independent assortment of two genes, with each having a 3:1 ratio in a monohybrid cross (3/4 dominant, 1/4 recessive).

Q2: What does the chi-square value tell me?
A: It measures how much your observed data deviates from the expected ratio. Lower values mean better fit (compare to critical values from chi-square tables).

Q3: When wouldn't I get a 9:3:3:1 ratio?
A: If genes are linked (on same chromosome), if there's epistasis, or with small sample sizes due to random chance.

Q4: How many offspring do I need for reliable results?
A: At least 16 for the minimum expected count to be 1, but more is better for statistical significance.

Q5: Can I use this for trihybrid crosses?
A: No, trihybrid crosses have a 27:9:9:9:3:3:3:1 ratio - you'd need a different calculator.