NCERT · Class 12 · Biology · Principles of Inheritance and VariationIn a certain plant species, red flower color (R) is dominant over white flower color (r). If a homozygous red-flowered plant is crossed with a homozygous white-flowered plant, what will be the genotype and phenotype of the F1 generation? Further, if plants of the F1 generation are self-pollinated, calculate the expected phenotypic and genotypic ratios in the F2 generation using a Punnett square.

To determine the genotype and phenotype of the F1 and F2 generations, we apply Mendel's Law of Segregation and Dominance.

Step 1: Parents Identification

• Homozygous red-flowered plant genotype = $RR$
• Homozygous white-flowered plant genotype = $rr$

Step 2: Gamete Formation

• Plant $RR$ produces gametes containing allele $R$.
• Plant $rr$ produces gametes containing allele $r$.

Step 3: F1 Generation\nWhen these gametes fuse during fertilization, the genotype of all offspring in the F1 generation will be $Rr$.

• Phenotype of F1 generation: All plants will have red flowers because the allele for red color ($R$) is completely dominant over the allele for white color ($r$).

Step 4: F2 Generation (Self-pollination of F1)\nCross: $Rr \times Rr$

• Gametes produced by F1 plants: $R$ and $r$ (in equal proportion).

Punnett Square for F2 Generation:

Step 5: Ratios Calculation

• Genotypic Ratio:

  • $RR$ (Homozygous dominant) = 1
  • $Rr$ (Heterozygous) = 2
  • $rr$ (Homozygous recessive) = 1
  • Ratio = 1 : 2 : 1

• Phenotypic Ratio:

  • Red flowers ($RR$ and $Rr$) = 3
  • White flowers ($rr$) = 1
  • Ratio = 3 : 1