Ant 101 Lecture 2 note on Mendelian Genetics

Key Concepts of Mendelian Genetics

  • Genetics

    • Study of heredity.
    • Understands how traits are passed from parents to offspring.

  • Foundations of Inheritance

    • Principles derived from the work of Gregor Mendel in the 19th century, especially regarding genes, chromosomes, and meiosis.

  • Mendel’s Experiments

    • Conducted from 1856-1866 with over 30,000 pea plants.
    • Investigated discontinuous traits to refute the idea of blending inheritance, where traits are thought to blend in offspring.
    • Discontinuous traits maintain distinct inheritance patterns.

Mendel's Methodology

  • Self-Fertilization of Pea Plants

    • Pea plants reproduce by self-fertilization, allowing consistent offspring display.
    • Hybridization involved cross-fertilization between different plants, creating distinct parent (P), filial (F1), and subsequent generations (F2, F3).

  • Generational Analysis

    • P Generation: Parental generation involved in the initial cross.
    • F1 Generation: Offspring from P generation hybrids.
    • F2 Generation: Offspring resulting from F1 self-fertilization.
    • Notable characteristic ratios emerge during these generations.

Key Traits Analyzed by Mendel

  • Traits Mendel studied:
    • Plant height
    • Seed texture
    • Seed color
    • Flower color (e.g., white vs. violet)
    • Pea pod size
    • Pea pod color
    • Flower position

Mendel's Findings on Flower Color

  • In flower coloration experiments:

    • All offspring from white flowers were white (homozygous).
    • All offspring from violet flowers were violet, showcasing dominance of the violet trait.
    • Hybrid F1 generation: all violet, indicating dominant trait expression.
    • F2 generation: display of 75% violet and 25% white flowers.

  • Dominant and Recessive Traits

    • Dominant Traits: Expressed in hybrids (e.g., violet).
    • Recessive Traits: Hidden in hybrids (e.g., white) and reappear in F2 generation.

Genetic Terminology

  • Alleles: Different versions of a gene.
  • Genotype: Genetic makeup (e.g. TT, Tt, tt).
  • Phenotype: Observable characteristics (e.g. tall or short).
  • Homozygous: Identical alleles for a trait (TT or tt).
  • Heterozygous: Different alleles for a trait (Tt).

Laws of Inheritance (Mendel's Laws)

  • Law of Segregation: Genes segregate equally into gametes, allowing for predictable offspring traits based on parental genotypes.
  • Law of Independent Assortment: Genes adhere to independent sorting into gametes, enabling varied allele combinations without influence from other genes.
  • Law of Dominance: Dominant traits are expressed in the presence of recessive alleles; recessive traits are only visible in homozygous recessive individuals.

Sex-Linked Traits

  • X-Linked Traits: Found on the X chromosome, leading to unique inheritance patterns between genders (e.g., color blindness, hemophilia). These traits often exhibit different frequencies in males and females due to the presence of one X chromosome in males.

Human Discontinuous Traits

  • Examples include albinism (recessive) and color blindness (X-linked).
  • Traits such as freckles and hair color illustrate Mendelian inheritance patterns where recessive traits can re-emerge in the population.