Mendel and Principles of Genetics

Heredity, Genetics, and Traits

• Heredity: Passing of characteristics from parents to offspring.

• Genetics: The study of heredity.

• Traits: The characteristics inherited from parents.

Gregor Mendel’s Contributions

• Background:

  • Monk from Austria known for his work in genetics.

  • Conducted experiments in his monastery's garden.

  • Studied mathematics and botany, applying the scientific method.

  • Took meticulous notes of his observations.

Study of Pea Plants

• Why Pea Plants?

  • Pea plants reproduce sexually, having both male and female gametes.

  • Allowed Mendel to control which plants were crossed.

  • Simple traits (such as shape and color) were easy to study.

Traits in Pea Plants

• Dominant and Recessive Traits:

  • Examples include:

  • Seed shape: round (dominant) vs. wrinkled (recessive)

  • Seed color: yellow (dominant) vs. green (recessive)

  • Flower color: purple (dominant) vs. white (recessive)

  • Pod shape: inflated (dominant) vs. constricted (recessive)

  • Plant height: tall (dominant) vs. short (recessive)

Sexual Reproduction in Pea Plants

• Gametes:

  • Male gamete = pollen

  • Female gamete = ovule

• Fertilization: Uniting of male and female gametes leading to seed formation.

Mendel’s Experiments

• Monohybrid Cross: Focused on a single trait.

  • Example: Crossed true-breeding tall (TT) and short (tt) plants.

• Results:

  • F1 Generation: All offspring were tall.

  • F2 Generation: Ratio of 3 tall to 1 short (75% tall, 25% short).

Generations Explained

• P1: Parent generation (e.g., tall & short plants).

• F1: First generation (all tall).

• F2: Second generation (3 tall and 1 short).

Dominance and Segregation

• Rule of Dominance:

  • Dominant traits mask recessive traits in the F1 generation.

• Law of Segregation:

  • Alleles for each trait separate during gamete formation.

Genes and Alleles

• Genes: Factors that determine traits, located on chromosomes.

• Alleles: Different forms of a gene (e.g., T for tallness, t for shortness).

• Genotype: Organism's genetic makeup (TT, Tt, tt).

• Phenotype: Physical appearance based on genotype.

Independent Assortment

• Law of Independent Assortment:

  • Genes for different traits are inherited independently of each other, leading to genetic variation.

Dihybrid Cross

• Example of Dihybrid Cross: Mendel crossed round yellow seeds (RRYY) with wrinkled green seeds (rryy).

  • F1 Results: All offspring had round yellow seeds.

  • F2 Results: Observed 9:3:3:1 ratio of phenotypes (round yellow : round green : wrinkled yellow : wrinkled green).

Chromosomal Basis of Inheritance

• Homologous Chromosomes: Each pair consists of one chromosome from each parent.

• Diploid (2n) and Haploid (n):

  • Body cells have two sets of chromosomes (diploid).

  • Gametes (sperm and eggs) have one set (haploid).

Meiosis and Gamete Formation

• Meiosis: Process that reduces chromosome number by half, producing haploid gametes.

  • Meiosis I: Reduction from diploid to haploid.

  • Meiosis II: Separation of sister chromatids, resulting in 4 haploid cells.

Conclusion on Sexual Reproduction

• Definition: The fusion of haploid sex cells (sperm and egg) resulting in a diploid zygote after fertilization.

(Note: Include diagrams of Punnett Squares and various crosses where relevant to enhance understanding.)