Direct Answer
Gregor Johann Mendel (the Father of Modern Genetics) formulated the fundamental principles of biological heredity in 1865 based on his hybridization experiments with garden pea plants (*Pisum sativum*):
1. First Law: Law of Dominance
2. Second Law: Law of Segregation (Purity of Gametes)
3. Third Law: Law of Independent Assortment
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Detailed Breakdown of the Three Laws
#### 1. Law of Dominance
- Statement: When two homozygous individuals with contrasting characters (e.g., pure tall $TT$ and pure dwarf $tt$) are crossed, only one character appears in the first filial ($F_1$) generation. This expressed trait is Dominant, while the unexpressed suppressed trait is Recessive.
- Example: Crossing pure Tall ($TT$) with pure Dwarf ($tt$) produces $100\%$ Tall ($Tt$) offspring in $F_1$.
#### 2. Law of Segregation (Purity of Gametes)
- Statement: The two alleles of a gene pair do not blend or contaminate each other; during the formation of gametes (meiosis), the paired alleles separate (segregate) randomly so that each gamete carries only one allele.
- Monohybrid Cross Ratios ($F_2$ Generation):
- Phenotypic Ratio: $\mathbf{3 : 1}$ (3 Tall : 1 Dwarf)
- Genotypic Ratio: $\mathbf{1 : 2 : 1}$ ($1\ TT : 2\ Tt : 1\ tt$)
#### 3. Law of Independent Assortment
- Statement: When two pairs of contrasting traits are combined in a hybrid (dihybrid cross), the segregation of alleles of one gene pair is completely independent of the segregation of alleles of the other gene pair during gamete formation.
- Dihybrid Cross Ratios ($F_2$ Generation - Round/Yellow vs Wrinkled/Green):
- Phenotypic Ratio: $\mathbf{9 : 3 : 3 : 1}$
- 9 Round Yellow ($R_{-}Y_{-}$)
- 3 Round Green ($R_{-}yy$)
- 3 Wrinkled Yellow ($rrY_{-}$)
- 1 Wrinkled Green ($rryy$)
