Lecture Notes: Non-Mendelian Genetics and Pedigrees

Introduction

• Topic: Non-Mendelian Genetics (Chapter 14)
• Review: Mendelian Genetics
  • Traditional genetic understanding: two genes, one from each parent, dominance, and recessiveness.
  • Non-Mendelian: Genes don't always follow Mendel’s rules.

Non-Mendelian Genetics

Incomplete Dominance

• Previously discussed: Incomplete dominance.
• Example: Red flower + White flower = Pink flower.

Multiple Alleles

• More than two alleles for a trait in a population.
• Example: ABO blood groups.
  • Population has A, B, O alleles.
  • Individuals inherit only two of these alleles.
  • A & B are dominant over O.

Co-Dominance

• Both traits expressed equally.
• Example: AB blood type (both A and B expressed)
• Example in animals: Black cow + White cow = Black and white spots.

Concepts in Blood Groups

• Genotypes: AA, AO, BB, BO, OO, AB.
• Rh Factor: Treat as Mendelian (Positive is dominant over Negative).
  • Complications in pregnancy with RH negative mother and RH positive baby.

Pleiotropy

• One gene affects multiple traits.
• Example: Sickle cell gene affects anemia, oxygen concentration, and malaria resistance.
• Example: Frizzled chickens affect feather appearance, metabolic rate, and egg laying.

Epistasis

• One gene interferes with the expression of another.
• Example: Labrador retriever coat color.
  • B and E genes interaction.
  • Black, chocolate, and golden labs based on gene combination.

Polygenic Inheritance

• Trait influenced by multiple genes.
• Example: Eye color, skin color, hair color.
  • Complex interactions beyond Mendelian inheritance.

Pedigrees

• Used to track inheritance through generations.
• Symbols: Circles (female), squares (male), filled (affected), lines (relationships and offspring).

Analyzing Pedigrees

• Determine mode of inheritance (autosomal recessive, autosomal dominant, etc.).
• Examples:
  • Autosomal recessive: Cystic fibrosis, Tay-Sachs, Sickle cell.
  • Autosomal dominant: Huntington's disease, Echondroplasia.

Practice and Support

• SI sessions and office hours available for additional practice.
• Resources: Web courses, problem sheets, and quizzes for self-study.

Future Topics

• Continue with pedigrees next session.
• Introduction to Chapter 15.

Conclusion

• Non-Mendelian genetics provides a broader and more complex understanding of inheritance beyond Mendel’s initial findings.
• Pedigrees are essential for tracing and understanding genetic traits and disorders in families.