LECTURE CONNECTIONS

3 | Basic Principles of Heredity © 2009 W. H. Freeman and Company

Chapter 3 Outline

• 3.1 Gregor Mendel Discovered the Basic Principles of Heredity, 44

• 3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance, 47

• 3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment, 57

• 3.4 Observed Ratios of Progeny May Deviate from Expected Ratios by Chance, 62

3.1 Gregor Mendel Discovered the Basic Principles of Heredity

• Gregor Mendel and his success in genetics

• Genetic Terminology

• What Monohybrid Crosses Reveal

• Predicting the Outcomes of Genetic Crosses

• The Testcross

• Incomplete Dominance

• Genetic Symbols

3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance

• Conclusion 1: One character is encoded by two genetic factors.

• Conclusion 2: Two genetic factors (alleles) separate when gametes are formed.

• Conclusion 3: The concept of dominant and recessive traits.

• Conclusion 4: Two alleles separate with equal probability into the gametes.

Monohybrid cross: cross between two parents that differ in a single characteristic

3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance

• Principle of segregation: (Mendel’s first law)Each individual diploid organism possesses two alleles for any particular characteristic. These two alleles segregate when gametes are formed, and one allele goes into each gamete.

• The concept of dominance: When two different alleles are present in a genotype, only the trait encoded by one of them – the “dominant” allele – is observed in the phenotype.

3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance

• Relating Genetic Crosses to Meiosis

• Chromosome theory of heredity

3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance

• Predicting the outcomes of genetics crosses

• The Punnett square

3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance

• The Testcross

• Incomplete Dominance

• Ratios in Simple Crosses

3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment

• Dyhybrid Crosses• The Principle of Independent Assortment• Relating the Principle of Independent

Assortment to Meiosis• Applying Probability and the Branch Diagram to

Dihybrid Crosses• Dihybrid Testcross