Ever wondered how we know if a genetic cross experiment fits Mendelian ratios? It's like trying to guess the secret recipe of a dish just by tasting it. This is where chi-squared tests come to the rescue!

In a chi-squared test, you have

• H0 (Null Hypothesis): Everything is as expected; no surprises! It's like your mom telling you to clean your room, and lo and behold, it's already clean.

  🌍 Real-world example: In a genetics test, if you're expecting a 3:1 ratio, this hypothesis says, "Yep, it'll be 3:1."

• H1 (Alternative Hypothesis): Something fishy is going on; the results are not as expected. This would be like finding a sock in your soup 🧦🍲.

  🌍 Real-world example: In the same genetics test, this hypothesis says, "Nope, it's not gonna be 3:1. Something else is up!"

• State Hypotheses: Write down your H0 and H1.
• Create Contingency Table: It's like a bingo card but for your observed data.
• Calculate Expected Proportions: Use the good ol' Mendelian ratios like 9:3:3:1 to figure out what you should expect.
• Degrees of Freedom: Sounds like a rock band, but it's just the number of categories minus 1. (4 - 1) = 3 🎸
• Critical Region: Use a chi-squared table and find the value that corresponds to your degrees of freedom. Think of this as the tipping point for your hypothesis.
• Do the Math: Plug your observed and expected numbers into the chi-squared equation
• χ² = Σ(obs − exp)² / exp
• Final Verdict: Compare your chi-squared value to the critical region. If it's lower, H0 stays. If higher, H0 goes out the window 🪟.

🌍 Real-world example: Bateson in 1901 tested chicken feather and comb traits. He found out that they fit the expected 9:3:3:1 ratio! The genes were indeed unlinked, just like your Wi-Fi when it goes off at crucial times.