Understanding Mendelian Genetics Concepts

Nov 20, 2024

Mendelian Genetics Lecture Notes

Introduction to Mendelian Genetics

  • Presenter: Mr. Andersen
  • Named After: Gregor Mendel
    • Contributions to genetics
    • Worked with pea plants to discover genetic principles
  • Comparison: Charles Darwin was known in his time; Mendel died in obscurity
  • Modern Synthesis: Combination of Mendel's and Darwin's theories

Mendel's Experiments and Discoveries

  • Pea Plant Crosses:
    • Mendel transferred pollen using a paintbrush
    • Pea plants: fast-growing, multiple characteristics
    • Identified two key genetic principles:
      • Law of Segregation
      • Law of Independent Assortment

Mendel's Laws Explained

  • Law of Segregation:

    • Alleles separate during gamete formation
    • Probability of receiving a specific allele is 50%
    • Demonstrated using a coin flip analogy
  • Law of Independent Assortment:

    • Genes for different traits are inherited independently
    • Example: Hitchhiker's thumb and attached earlobe do not affect each other
    • Exceptions: Linked genes (e.g., red hair and freckles)

Mendelian Genetics in Practice

  • Punnett Squares:
    • Tool for predicting genetic outcomes
    • 3:1 ratio of dominant to recessive traits observed
    • Example: Purple (dominant) vs. white (recessive) flowers

Practice Problems

  1. Coin Flip Probability:

    • 1/2 probability for heads or tails regardless of previous results
  2. Heterozygous vs. Homozygous Classification:

    • Homozygous dominant: e.g., RR
    • Heterozygous: e.g., Rr (also called hybrids)
  3. Phenotype Determination:

    • Genotype: Genetic makeup (e.g., Yy)
    • Phenotype: Physical appearance (e.g., yellow)
  4. Cross Probability Problems:

    • Monohybrid crosses using Punnett squares
    • Example: Round (R) vs. wrinkled (r) seeds

Genetic Disorders

  • Huntington's Disease:

    • Causes degeneration of nerve fibers, leading to serious symptoms
    • Dominant genetic disorder
    • Example pedigree analyzed
  • Ethical Considerations:

    • Genetic testing implications
    • Questions about knowing one's genetic fate
    • Insurance concerns

Conclusion

  • Mendelian genetics provides a basis for understanding heredity
  • Raises ethical and privacy issues in modern genetic testing
  • Preview: Linked genes and complex genetics in the next lecture