Mastering Mendel: AP Biology study guide for pea plant experiments.

🧬 Introduction to Mendel's Experiments

Gregor Mendel, through his experiments with pea plants, laid the foundation for the science of genetics. His work demonstrated the principles of inheritance, including the concepts of dominant and recessive traits, segregation, and independent assortment. Understanding these principles is crucial for AP Biology students.

🧪 Objectives

• 🎯 Define key genetic terms such as genotype, phenotype, allele, homozygous, and heterozygous.
• 🌱 Explain Mendel's laws of segregation and independent assortment.
• 🔬 Predict the outcome of monohybrid and dihybrid crosses using Punnett squares.
• 📊 Analyze phenotypic ratios resulting from genetic crosses.

🔬 Materials

• 📝 Whiteboard or projector for presenting information.
• 🌱 Images or models of pea plants displaying different traits (e.g., seed color, seed shape).
• ➕ Punnett square worksheets.
• ✏️ Markers or pens.
• 🧮 Calculators for analyzing ratios (optional).

⏰ Warm-up (5 minutes)

Review of Basic Genetic Terminology:

• ❓ Ask students to define the following terms: gene, allele, dominant, recessive.
• 💬 Briefly discuss the answers as a class.

👨‍🏫 Main Instruction

🌱 Mendel's Laws

• 🔍 Law of Segregation: Each individual has two alleles for each trait, and these alleles separate during gamete formation. Each gamete receives only one allele.
• 🌱 Law of Independent Assortment: Alleles of different genes assort independently of one another during gamete formation. This law applies when genes are on different chromosomes or far apart on the same chromosome.

➕ Monohybrid Crosses

• 📝 A monohybrid cross involves one trait. For example, seed color (yellow or green).
• 📊 Use a Punnett square to predict the offspring genotypes and phenotypes.
• 💡 Example: If Y = yellow and y = green, cross a heterozygous plant (Yy) with another heterozygous plant (Yy).

The Punnett square would look like this:

• 📈 Genotypic ratio: 1 YY : 2 Yy : 1 yy
• 🌱 Phenotypic ratio: 3 yellow : 1 green

➗ Dihybrid Crosses

• 🧬 A dihybrid cross involves two traits. For example, seed color (yellow or green) and seed shape (round or wrinkled).
• 📊 Use a larger Punnett square (4x4) to predict the offspring genotypes and phenotypes.
• 💡 Example: If Y = yellow, y = green, R = round, and r = wrinkled, cross two heterozygous plants (YyRr x YyRr).

The phenotypic ratio for a dihybrid cross of two heterozygotes is typically 9:3:3:1.

📝 Assessment

✍️ Practice Quiz

1. ❓ In pea plants, tall (T) is dominant to short (t). What are the possible genotypes and phenotypes of the offspring when a heterozygous tall plant (Tt) is crossed with a short plant (tt)?
2. ❓ What is the phenotypic ratio of a monohybrid cross between two heterozygous individuals?
3. ❓ In guinea pigs, black fur (B) is dominant to white fur (b). If a homozygous black guinea pig (BB) is crossed with a homozygous white guinea pig (bb), what percentage of the offspring will have black fur?
4. ❓ Explain Mendel's Law of Segregation in your own words.
5. ❓ Explain Mendel's Law of Independent Assortment in your own words.
6. ❓ In tomatoes, red fruit (R) is dominant to yellow fruit (r), and tall plants (T) are dominant to short plants (t). A plant heterozygous for both traits (RrTt) is crossed with a plant that is homozygous recessive for both traits (rrtt). What is the expected phenotypic ratio of the offspring?
7. ❓ What is the purpose of using a Punnett square in genetic crosses?