Genetics Lecture Notes

Introduction

• Resources for Review: GIF review, study tips video, and the "Stroll Through the Playlist."
• Focus of Lecture: General genetic problems - Mendelian, non-Mendelian traits, and pedigrees.

Preparatory Advice

1. Tools Needed: Pen/pencil and paper.
2. Assumed Knowledge: Familiarity with genetic vocabulary.
3. Gene Symbols: Focus on concepts over symbols; ensure letters have distinct upper and lower case forms.
4. Probability in Genetics: Punnett squares show probability, not certainty.
5. Complexity of Genetics: Traits can be polygenic, pleiotropic, and influenced by epistasis or epigenetics.

Mendelian Genetics

One-Trait Crosses

• Example: Guinea pigs with alleles H (hair) and h (hairless).
• Genotypes: Homogeneous dominant (HH), heterozygous (Hh), homogeneous recessive (hh).
• Punnett Square: Cross hairless (hh) with heterozygous (Hh) guinea pigs.
  • Genotype Ratio: 1:1 (Hh:hh)
  • Phenotype Ratio: 1:1 (hair:hairless)

Two-Trait Crosses (Dihybrid)

• Example: Cats with traits for hair and love for sinks (H, S).
• Genotype Example: HhSs for both traits.
• Dihybrid Cross: 16 square box using FOIL method.
  • Phenotype Ratio: 9:3:3:1 for two heterozygote parents.

Non-Mendelian Genetics

Incomplete Dominance

• Example: Snapdragon flowers.
  • Genotypes: RR (red), R'R' (white), RR' (pink).
  • Offspring Ratios: 1 red, 2 pink, 1 white.

Codominance

• Example: Chicken colors.
  • Genotypes: BB (black), WW (white), BW (black and white speckled).
  • Offspring Ratios: 1:1 (BB:BW)

Multiple Alleles

• Example: Human blood types (A, B, AB, O).
  • Genotypes for Blood Types: IAIA, IAi (Type A); IBIB, IBi (Type B); IAIB (Type AB); ii (Type O).
  • Probability Example: 25% chance for Type O when crossing heterozygous Type A and B.

Sex-Linked Traits

• Example: Hemophilia (recessive, sex-linked).
  • Male Genotype with Disorder: XhY
  • Female Genotype with Disorder: XhXh
  • Inheritance Example: Male with hemophilia and homozygous dominant female results in 0% offspring with disorder.

Pedigrees

• Purpose: Track traits through generations.
• Shapes: Circles for females, squares for males.
• Example of Autosomal Recessive Trait: Shaded shapes have recessive genotype (ee).
• Identifying Genotypes: Start with shaded shapes.
  • Limitations: Cannot always determine heterozygous individuals without offspring data.
• Non-Sex-Linked Trait Example: Given genotype inconsistencies suggest non-sex-linked trait.

Conclusion

• Further Resources: Genetic Series videos, practice problems.
• Importance: Understanding genetics has real-world applications.