Monohybrid & Dihybrid Cross Simulator
An interactive Punnett square generator built on Mendel's Law of Segregation and Law of Independent Assortment. Set up parental genotypes, generate the cross, and read off genotypic and phenotypic ratios instantly.
1 · Set Up the Cross
2 · Punnett Square
3 · Genotypic & Phenotypic Ratios
Genotypic Ratio
Phenotypic Ratio
Study of Monohybrid Cross Using Punnett Square
Demonstrating Mendel's Law of Segregation through the F₂ generation
1Aim
To study a monohybrid cross using a Punnett square and determine the expected genotypic and phenotypic ratios in the F₂ generation.
2Principle
A monohybrid cross is a genetic cross involving the inheritance of one pair of contrasting characters. According to Mendel's principle of segregation, the two alleles of a gene separate during gamete formation, so that each gamete receives only one allele.
For example, consider plant height:
- T = Tall (dominant)
- t = Dwarf (recessive)
A cross between two heterozygous individuals is:
The resulting F₂ generation gives:
- Genotypic ratio = 1 TT : 2 Tt : 1 tt
- Phenotypic ratio = 3 Tall : 1 Dwarf
Thus, the monohybrid cross demonstrates Mendel's Law of Segregation.
3Materials Required
- Genetics practical chart / model
- Punnett square chart or worksheet
- Pencil and ruler
- Practical record book
- Computer / mobile or genetics simulation software, if available
4Genetic Symbols
| Symbol | Meaning |
|---|---|
| T | Dominant allele for tallness |
| t | Recessive allele for dwarfness |
| TT | Homozygous dominant |
| Tt | Heterozygous |
| tt | Homozygous recessive |
5Procedure
Step 1: Select the parental characters
Consider Tall (T) as dominant and dwarf (t) as recessive.
Step 2: Write the parental cross
The pure-breeding parental cross is:
Step 3: Determine the gametes
- The TT parent produces only T gametes.
- The tt parent produces only t gametes.
Step 4: Determine the F₁ generation
All offspring receive one T allele from each parent:
Therefore: F₁ = 100% Tt (Tall)
Step 5: Self-cross the F₁ generation
Cross the F₁ individuals:
Each parent produces two types of gametes: T and t
Step 6: Construct the Punnett Square
| × | T | t |
|---|---|---|
| T | TT | Tt |
| t | Tt | tt |
6Observation
The four possible offspring combinations are:
- TT – Tall
- Tt – Tall
- Tt – Tall
- tt – Dwarf
Genotypic Ratio
Phenotypic Ratio
Observation Table
| Genotype | Number of Combinations | Phenotype |
|---|---|---|
| TT | 1 | Tall |
| Tt | 2 | Tall |
| tt | 1 | Dwarf |
| Total | 4 | — |
7Result
The monohybrid cross Tt × Tt produces an expected:
- Genotypic ratio = 1 : 2 : 1
- Phenotypic ratio = 3 : 1
The result demonstrates Mendel's Law of Segregation.
8Precautions
- Correctly identify dominant and recessive alleles.
- Use uppercase letters for dominant alleles and lowercase letters for recessive alleles.
- Determine the gametes before constructing the Punnett square.
- Do not confuse genotype with phenotype.
- Count all possible offspring combinations before calculating the ratio.
- Remember that the 3:1 ratio is an expected theoretical ratio; actual biological observations may vary.
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