Mendel&Gene_Mendelian_genetics_part1

Mendel and Genetics Overview

  • Heredity: Transmission of traits from one generation to the next.

  • Gregor Mendel: Published the theory of "Particulate Inheritance" in 1865; ignored initially, rediscovered in 1902.

Historical Context

  • Before Mendel: Concept of Blending Inheritance where traits mix evenly (e.g., red and white horses produce roan).

Mendel's Model Organism

  • Garden Pea (Pisum sativum): A hermaphroditic plant with both male and female reproductive organs.

Fertilization Techniques

  • Self-fertilization: Female organs receive pollen from the same plant.

  • Cross-fertilization:

    • Pollen is collected from one plant and transferred to the female organ of another plant, whose male organs have been removed.

Mendel's Experiments & Generations

  • P Generation: True-breeding parents (e.g., purple and white flowers).

  • F1 Generation: All offspring display the dominant trait (purple flowers).

  • F2 Generation: Resulting ratio of traits:

    • 3/4 purple flowers

    • 1/4 white flowers

Key Concepts in Mendelian Genetics

  • Each plant has two hereditary factors (alleles): dominant (P) and recessive (p).

  • Only one allele from each parent is passed to the offspring.

  • Dominance hierarchy:

    • Dominant allele leads to purple flowers (presence of P).

    • Recessive allele leads to white flowers (absence of P).

Punnett Square Analysis

  • Monohybrid Cross: Examines inheritance of one trait.

    • Example: PP (purple) x pp (white) results in 100% Pp (purple).

  • In F2 generation:

    • Genotype ratio: 1 PP : 2 Pp : 1 pp

    • Phenotype ratio: 3 purple : 1 white.

Mendel's Monohybrid Crosses

  • Investigated traits like seed shape:

    • Dominant: Round (R)

    • Recessive: Wrinkled (r)

  • Phenotype Ratio: 3 round : 1 wrinkled.

  • Genotype Ratio: 1 RR : 2 Rr : 1 rr.

Further Applications of Mendel's Laws

  • Law of Segregation:

    • Genes exist in alternative versions called alleles.

    • Each organism inherits two alleles, one from each parent.

    • If the alleles differ, the dominant allele dictates the organism's appearance.

Testcross Definition

  • A testcross involves mating an individual of unknown genotype with a homozygous recessive individual. This reveals whether the unknown genotype carries a recessive allele.