Test crosses Transitional Reasoning Download PDF

Questions

1. 1.

   A botanist studies a plant species in which purple flower color ($P$) is completely dominant over white flower color ($p$). To determine whether an unknown purple-flowered plant is homozygous or heterozygous, the botanist carries out a test cross with a white-flowered plant. The cross produces 82 purple-flowered and 78 white-flowered offspring. Based on this evidence, which statement correctly identifies the genotype of the unknown parent and predicts the phenotypic outcome if that parent had instead been homozygous dominant?

   • A) The parent genotype was $PP$; if it had been homozygous dominant, all offspring would have displayed white flowers.
   • B) The parent genotype was $Pp$; if it had been homozygous dominant, all offspring would have displayed purple flowers.
   • C) The parent genotype was $Pp$; if it had been homozygous dominant, a 1:1 ratio of purple to white flowers would have occurred.
   • D) The parent genotype was $pp$; if it had been homozygous dominant, a 3:1 ratio of purple to white flowers would have occurred.