Mendel's Experiments with Pea Plants

• Mendal, Mater ka poudha means "Mendel, pea plants"

Gregor Mendel

• Gregor Mendel was an Austrian monk and scientist
• He is known as the "father of modern genetics"
• Mendel lived from 1822 to 1884
• He conducted his landmark experiments on pea plants (Pisum sativum) in the monastery garden
• Mendel's work established the fundamental principles of heredity

Mendel's Experiments

• Mendel chose pea plants because they had distinct, easily observable traits
• The traits he studied included:
  • Seed shape (round or wrinkled)
  • Seed color (yellow or green)
  • Flower color (purple or white)
  • Pod shape (inflated or constricted)
  • Pod color (green or yellow)
  • Stem length (tall or dwarf)
  • Flower position (axial or terminal)
• Mendel used controlled breeding experiments by cross-pollinating plants with different traits
• He meticulously recorded the traits of the parent plants and their offspring

Mendel's Laws

• From his experiments, Mendel formulated three fundamental principles of inheritance
  • The Law of Segregation
  • The Law of Independent Assortment
  • The Law of Dominance

Law of Segregation

• States that each individual has two factors (alleles) for each trait
• These alleles segregate (separate) during the formation of gametes (sex cells)
• Each gamete carries only one allele for each trait
• During fertilization, the offspring receives one allele from each parent, restoring the pair
• The alleles combine randomly in each offspring

Law of Independent Assortment

• States that the alleles of different genes assort independently of one another during gamete formation
• This means that the inheritance of one trait (e.g., seed color) does not affect the inheritance of another trait (e.g., seed shape)
• Independent assortment occurs when genes are located on different chromosomes

Law of Dominance

• States that when an individual has two different alleles for a trait, one allele will be dominant and the other will be recessive
• The dominant allele masks the expression of the recessive allele
• The trait determined by the dominant allele will be the one that is expressed in the phenotype (observable characteristics)
• The recessive trait will only be expressed if the individual has two copies of the recessive allele

Genotype and Phenotype

• Genotype refers to the genetic makeup of an individual, i.e., the combination of alleles they possess
• Phenotype refers to the observable characteristics of an individual, which are determined by the genotype
• The genotype will contribute to the phenotype, with the dominant allele, if present, being expressed

Homozygous and Heterozygous

• Homozygous refers to having two identical alleles for a trait (e.g., AA or aa)
• Heterozygous refers to having two different alleles for a trait (e.g., Aa)
• Homozygous dominant refers to having two copies of the dominant allele (AA)
• Homozygous recessive refers to having two copies of the recessive allele (aa)

Punnett Squares

• Used to predict the genotypes and phenotypes of offspring from a genetic cross
• A Punnett square is a diagram that shows all possible combinations of alleles from the parents
• Each square in the Punnett square represents a possible genotype of an offspring

Monohybrid Cross

• A cross between individuals that are heterozygous for one trait (e.g., Aa x Aa)
• The phenotypic ratio of the offspring in a monohybrid cross is typically 3:1 (dominant : recessive)

Dihybrid Cross

• A cross between individuals that are heterozygous for two traits (e.g., AaBb x AaBb)
• The phenotypic ratio of the offspring in a dihybrid cross is typically 9:3:3:1

Significance of Mendel's Work

• Mendel's work laid the foundation for the field of genetics
• He demonstrated that traits are inherited in a predictable manner
• His laws of inheritance are still used today to understand how genes are passed from parents to offspring
• Mendel's work was initially overlooked, but it was rediscovered in the early 1900s
• It revolutionized the understanding of biology