Genetics Study Notes: Principles of Heredity

Chapter 3: Basic Principles of Heredity

The Chromosome Theory of Heredity

• Chromosomes segregate during meiosis and possess genes.
• Chromosomes in eukaryotes have a linear structure.

Mendel's Findings

• Each pea plant carries two alleles for a trait.
• Traits from both alleles are evident in the F₂ generation.

Segregation of Alleles

• Alleles are located on homologous chromosomes.
• Crossing over occurs in prophase I of meiosis.
• Homologous chromosomes separate during anaphase I.
• If crossing over occurs, chromatids may not be identical.

Monohybrid Crosses

• Reveals segregation and dominance principles.
• Uses Punnett squares for predicting outcomes.

Probability

• Probability predicts genetic cross outcomes.
• Multiplication Rule: $(P(A) * P(B))$ for independent events.
• Addition Rule: $(P(A) + P(B))$ for mutually exclusive events.

Dihybrid Crosses

• Examines two traits at once (e.g. seed shape and color).
• Shows independent assortment principle: allele pairs separate during meiosis.
• Expected F₂ phenotypic ratios: $(9:3:3:1)$ from dominant and recessive traits.

Conclusion of Dihybrid Crosses

• Principle of independent assortment reflects gamete formation during meiosis.
• Alleles at different loci assort independently.
• Techniques: F.O.I.L., Punnett squares, Branch Method for calculations.

Concepts of Segregation and Independent Assortment

• Both principles apply to anaphase I of meiosis.
• Segregation refers to separation of alleles, while independent assortment indicates that allele separation is independent of others.

Concept Checks

• Assesses understanding of alleles, ratios, and probabilities in genetic crosses.
• Example scenarios used to evaluate concepts, including probabilities for offspring traits.