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.