Introduction to Genetics and Mendel's Laws

Introduction to Genetics

• Genetics is the study of heredity
• Heredity is the passing of traits from parents to offspring
• Genetics studies how traits are passed
• The field of genetics is built around DNA molecules
• DNA molecules hold the genetic information for an organism
• A gene is a specific section of a DNA molecule that instructs cells to perform certain tasks
• A diagram shows human, cells, nucleus, chromosomes, and DNA.

Gregor Mendel

• Gregor Johann Mendel was an Austrian botanist, teacher, and Augustinian prelate.
• Mendel studied the inheritance of traits in pea plants.
• His genetic experiments with pea plants took eight years (1856-1863).
• He published his results in 1865.
• During this time, Mendel grew over 10,000 pea plants, meticulously tracking offspring traits.
• Mendel's experimental garden was located in the Czech Republic.
• Mendel is considered the Father of Genetics.
• He developed the laws of inheritance:
  • Law of Segregation
  • Law of Independent Assortment
  • Law of Dominance.

Pea Plant Experiments

• Peas (Pisum sativum) are suitable for genetic studies because:
  • They can be grown in a small area
  • They produce pure plants when self-pollinated across generations
  • They have many offspring
  • They can be artificially cross-pollinated

Reproduction in Flowering Plants

• Pollen contains sperm, produced by the stamen.
• The ovary contains eggs, inside the flower
• Pollen carries sperm to the ovules for fertilization.
• Self-fertilisation occurs in the same flower.
• Cross-fertilisation occurs between flowers.

Pea Plant Traits

• Table of traits studied by Mendel:
  • Seed shape (smooth/wrinkled)
  • Seed color (yellow/green)
  • Pod shape (inflated/wrinkled)
  • Pod color (green/yellow)
  • Flower color (purple/white)
  • Flower position (on stem/at tip)
  • Stem length (tall/dwarf).

DNA, Chromosomes, and Genes

• Mendel's work predated the discovery of DNA and chromosomes
• He stated that physical traits were inherited as "particles"

Genetic Terminology

• Allele: a specific variation of a gene (e.g., blue eyes, green eyes, blood type A, brown skin). Organisms have two alleles for each gene
• Trait: a physical characteristic that can be passed from parent to offspring (e.g., eye color, hair color, height).
• Dominant Allele: a trait that is expressed / show off in an organism. Represented by a capital letter. (example, black hair)
• Recessive Allele: a trait that is masked/ hidden by a dominant trait represented by a lowercase letter. (example, brown hair)
• Homozygous Alleles (PURE): a pair of alleles that produce a characteristic that is the same (e.g. BB or bb).
• Homozygous Dominant (BB): A genotype where both alleles are dominant
• Homozygous Recessive (bb): A genotype where both alleles are recessive
• Heterozygous (Bb): A genotype where one allele is dominant and the other is recessive.
• Genotype: the genetic make-up of an organism (e.g., Bb, BB, bb). This contributes to the organism's phenotype.
• Phenotype: the physical feature resulting from a genotype (e.g., Bb = black hair, BB = black hair, bb = brown hair)

Punnett Square

• A square diagram to predict genotypes of breeding experiments or crosses.

• Used by biologists to determine offspring genotype probability.

• (Example) Genotype & Phenotype in flowers.

  • R= Red flower
  • r = Yellow flower
  • RR= Red
  • Rr = Red
  • rr = Yellow