In the datura plant, purple flower color is controlled by a dominant allele P. White flowers are found in plants homozygous for the recessive allele p. Suppose that a purple-flowered datura plant with an unknown genotype is self-fertilized and that its progeny are 28 purple-flowered plants and 10 white-flowered plants.

If one of the purple-flowered progeny plants is selected at random and self-fertilized, what is the probability it will breed true?

Key Concepts

Dominant and Recessive Alleles

In genetics, alleles are different forms of a gene. A dominant allele, such as P in the datura plant, masks the effect of a recessive allele (p). This means that if at least one dominant allele is present, the dominant trait (purple flowers) will be expressed. Conversely, the recessive trait (white flowers) is only expressed when an organism is homozygous for the recessive allele (pp).

Genotype and Phenotype

The genotype refers to the genetic makeup of an organism, while the phenotype is the observable physical or biochemical characteristics. In this case, the purple-flowered datura plant could have a genotype of either homozygous dominant (PP) or heterozygous (Pp). Understanding the relationship between genotype and phenotype is crucial for predicting the traits of offspring in genetic crosses.

Punnett Square and Probability

A Punnett square is a tool used to predict the genotypes of offspring from a genetic cross. By analyzing the genotypes of the parent plants, one can calculate the probability of obtaining a specific phenotype in the progeny. In this scenario, determining the probability that a randomly selected purple-flowered progeny will breed true (PP) involves understanding the ratios of the genotypes produced from the self-fertilization of the purple-flowered parent.