Three independently assorting genes (A, B, and C) are known to control the following biochemical pathway that provides the basis for flower color in a hypothetical plant:

Three homozygous recessive mutations are also known, each of which interrupts a different one of these steps. Determine the phenotypic results in the F₁ and F₂ generations resulting from the P₁ crosses of true-breeding plants listed here:
colorless (aaBBCC) × green (AABBcc)

Verified step by step guidance

1. Identify the genotypes of the parent plants: one is colorless with genotype aaBBCC, and the other is green with genotype AABBcc. Each gene (A, B, C) controls a step in the pathway, and recessive homozygous mutations interrupt these steps.
2. Determine the F1 genotype by crossing the parents: since the parents are homozygous, the F1 offspring will be heterozygous at all loci where parents differ. The F1 genotype will be AaBbCc.
3. Analyze the F1 phenotype by considering the pathway and dominance: since A, B, and C are dominant alleles, the F1 plant will have all dominant alleles present, allowing the pathway to proceed fully to the speckled phenotype.
4. Set up the F2 generation by self-crossing the F1 plants (AaBbCc × AaBbCc). Use a Punnett square or the product rule to determine the genotypic ratios for each gene independently, as the genes assort independently.
5. Determine the phenotypic classes in the F2 by applying the pathway logic: for each genotype, check if the dominant allele is present at each gene to allow progression through the pathway steps (colorless → yellow → green → speckled). For example, if a plant is homozygous recessive at gene A (aa), it will be colorless regardless of B and C genotypes, and so on.

Key Concepts

Independent Assortment of Genes

Independent assortment refers to the principle that genes located on different chromosomes are inherited independently of each other. In this question, genes A, B, and C assort independently, meaning the alleles for each gene segregate without influencing the others, which affects the genotypic and phenotypic ratios in offspring.

Biochemical Pathway and Gene Function

The biochemical pathway shows a sequential process where each gene controls a step converting one pigment to another: A converts colorless to yellow, B converts yellow to green, and C converts green to speckled. Mutations in any gene block the pathway at that step, resulting in accumulation of the previous pigment and affecting flower color.

Genotypic and Phenotypic Ratios in Crosses

Understanding how to predict F1 and F2 generation phenotypes requires knowledge of Mendelian genetics, including how homozygous recessive mutations affect phenotype and how to use Punnett squares to determine offspring genotypes and phenotypes from given parental crosses.