Lecture Notes: Inheritance and Genetics - Part 2

1. Introduction

• Part 2 of heredity and genetics series.
• Builds on Part 1: Heredity, Punnett squares, and basic inheritance.
• Focus on more advanced problems and concepts.

2. Review of Basic Concepts

• Complete Dominance: Dominant allele completely masks recessive allele in heterozygous individuals (e.g., red flower covers white).

3. Incomplete Dominance

• Definition: Neither allele is truly dominant, resulting in an intermediate phenotype.
• Example: Flower color can be red, white, or pink (incomplete dominance results in pink).
• Phenotypic Ratios in Generations:
  • F1 Generation: All heterozygous (intermediate phenotype)
  • F2 Generation: Show all possibilities (homozygous dominant, heterozygous, homozygous recessive).

4. Co-Dominance

• Definition: Both alleles in a heterozygous individual are fully expressed.
• Example: Blood typing (A, B, AB, O) - A and B antigens are co-dominant.
• Phenotype Characteristics:
  • Blood Type A (AA or AO)
  • Blood Type B (BB or BO)
  • Blood Type AB (co-dominance: both A and B antigens)
  • Blood Type O (no A or B antigens)

5. Dihybrid Crosses

• Concept: Inheritance of two different traits simultaneously.
• Example: Freckles and red hair (often inherited together but can be independently assorted).
• Procedure: Step-by-Step Explanation
  • Identify parent genotypes
  • Determine possible gametes
  • Construct a Punnett Square for dihybrid cross
• Outcome: Provides all possible combinations of traits.

6. Mendelian Inheritance Patterns

• Autosomal vs. Sex-Linked Inheritance
  • Autosomal Dominant: One allele needed to express the trait.
  • Autosomal Recessive: Two alleles needed to express the trait (e.g., sickle cell anemia).
  • Sex-linked (X-linked): Traits found on X or Y chromosome.

7. X-Linked Inheritance

• Example: Color blindness is X-linked recessive, more common in males due to single X chromosome.
• Punnett Square Approach: Determining offspring phenotype and gender outcomes based on parental genotypes.

8. Using Punnett Squares for Genetic Predictions

• Through examples like sickle cell anemia and color blindness, how to predict possible genetic outcomes:
  • Heterozygous Parents (Carrier):
    • 25% healthy, non-carrier offspring
    • 50% healthy carrier offspring
    • 25% affected offspring

9. Pedigrees

• Purpose: Visual representation of trait inheritance across generations (e.g., affected, carriers, unaffected individuals).

10. Conclusion

• Importance of practice with Punnett squares and understanding different genetic inheritance patterns.
• Encouragement to review additional practice materials provided in course resources.

Note: Ensure to review Part 1 for foundational concepts and utilize additional practice problems to reinforce understanding.