Lecture Notes on Gregor Mendel and Genetics

Introduction to Gregor Mendel

• Gregor Mendel is known as the father of genetics.
• He was an Austrian monk who used pea plants to discover the laws of inheritance.
• Mendel's work predated the discovery of DNA and genes and was misunderstood in the 19th century.
• Today, his contributions are foundational in the field of genetics.

Key Genetic Concepts

• Alleles: Variants of a gene. Important for predicting phenotypes and genotypes of offspring.
• Phenotype: Physical characteristics, e.g., eye color.
• Genotype: Genetic makeup, e.g., combination of alleles inherited from parents.

Example: Eye Color Inheritance

• Mother's phenotype: Blue eyes (recessive allele, denoted as 'bb').
• Father's phenotype: Brown eyes (dominant allele 'B', genotype 'Bb').
• Genetic Prediction Using Punnett Squares:
  • Split the alleles into separate gametes for both parents.
  • Combine alleles to predict offspring genotypes.
  • Offspring Genotypes:
    • Two 'Bb' (Brown eyes, 50%)
    • Two 'bb' (Blue eyes, 50%)
  • Offspring Phenotypes:
    • Brown eyes: Dominant allele leads to brown eyes (50%).
    • Blue eyes: Recessive allele leads to blue eyes (50%).

Ratios and Probabilities

• Genotype Ratio: 1 Bb : 1 bb
• Phenotype Ratio: 1 Brown : 1 Blue

Example: Pea Plant Cross

• Heterozygous Parents: Both have genotype 'Ss' (smooth is dominant, wrinkled is recessive)
• Use Punnett Squares to predict outcomes:
  • Offspring Genotypes:
    • 1 'SS' (25%)
    • 2 'Ss' (50%)
    • 1 'ss' (25%)
  • Genotype Ratio: 1 SS : 2 Ss : 1 ss
  • Phenotypes:
    • Smooth (75%)
    • Wrinkled (25%)
  • Phenotype Ratio: 3 Smooth : 1 Wrinkled

Sex Inheritance

• Chromosomes:
  • Female: XX
  • Male: XY
• Punnett Square Prediction:
  • 50% Offspring male (XY)
  • 50% Offspring female (XX)

Quick Review Questions

1. Homozygous: Having two identical alleles for a trait.
2. Punnett Square Completion:
   • Genotypes: 50% 'DD', 50% 'Dd'
   • Phenotypes: 100% no dimples (dominant trait).
3. Sex Chromosomes for Females: XX

Conclusion

• Mendel's principles provide a framework for understanding inheritance and genetic prediction.
• Be familiar with making and interpreting Punnett squares and understanding genotype and phenotype ratios.

Next Topic: Inherited Disorders