A one-gene cross in pea plants
"A one-gene cross in pea plants" is a free, interactive Class 12 Biology simulation for NEET, built on the lesson "Inheritance of one gene: dominance and segregation" in Principles of Inheritance and Variation. A true-breeding tall plant (TT) × a dwarf plant (tt). Each parent puts one allele into each gamete; every box is one way the gametes can meet. Try other parents. Law of segregation: the two alleles of a gene separate when gametes form, so each gamete carries only one. Crossing with the homozygous recessive (a test cross) reads out an unknown genotype directly from the offspring.
From the lesson Inheritance of one gene: dominance and segregation in Principles of Inheritance and Variation. Change the values and watch what happens.
The idea behind it
NCERT § "Inheritance of One Gene"
- In a monohybrid cross of tall with dwarf pea, all F₁ plants were tall. Self-pollinating F₁ gave F₂ plants in a 3 tall : 1 dwarf ratio, and the dwarf plants were as dwarf as the original parent, with no blending.
- Mendel said a stable 'factor' passes each character from parent to offspring; these factors are now called genes. Alternative forms of one gene are alleles, such as T and t.
- A plant with two identical alleles (TT or tt) is homozygous; one with two different alleles (Tt) is heterozygous. Tt is a hybrid that looks tall, so genotype and phenotype are not the same thing.
- The F₂ genotypic ratio is 1 TT : 2 Tt : 1 tt, while the phenotypic ratio is 3 tall : 1 dwarf. The Punnett square, drawn by Reginald C. Punnett, is used to work these out.
- A test cross crosses an organism of unknown genotype showing the dominant trait with the recessive parent. A 1:1 result shows it was heterozygous; all-dominant offspring show it was homozygous.
- Law of dominance: characters are controlled by paired factors, and in a dissimilar pair one factor is expressed (dominant) while the other is masked (recessive). It explains why only one parental form shows in F₁ and both show in F₂.
- Law of segregation: the two alleles of a pair do not blend; they separate during gamete formation so each gamete gets only one of them. A homozygote makes one kind of gamete, a heterozygote two kinds in equal numbers.
Questions
2 answers
- What does the "A one-gene cross in pea plants" simulation show?
- A true-breeding tall plant (TT) × a dwarf plant (tt). Each parent puts one allele into each gamete; every box is one way the gametes can meet. Try other parents.
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Inheritance of one gene: dominance and segregation" in Principles of Inheritance and Variation (Class 12 Biology).
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