Suppose a flower had normal expression of genes A and C and expression of gene B in all four whorls. Based on the ABC hypothesis, what would be the structure of that flower, starting at the outermost whorl? a. carpel-petal-petal-carpel b. petal-petal-stamen-stamen c. sepal-carpel-carpel-sepal d. sepal-sepal-carpel-carpel

Verified step by step guidance

1. Understand the ABC hypothesis: This hypothesis explains the role of three classes of genes (A, B, and C) in determining the identity of floral organs in the four concentric whorls of a flower. Gene A affects the sepals, gene B affects the petals, and gene C affects the carpels. Gene A functions in whorls 1 and 2, gene B in whorls 2 and 3, and gene C in whorls 3 and 4.
2. Analyze gene expression in the given flower: The flower expresses gene A and C normally, but gene B is expressed in all four whorls. This abnormal expression of gene B alters the typical floral structure.
3. Determine the effect of gene B expression in all whorls: Normally, gene B is only active in the second and third whorls, contributing to the formation of petals and stamens. However, in this scenario, the presence of gene B in all whorls suggests that its influence might override the effects of genes A and C in their respective whorls.
4. Predict the floral structure: Since gene B promotes petal formation in the second whorl and stamen formation in the third whorl, its expression in all whorls could potentially convert all whorls into petal and stamen structures. The first and second whorls might develop as petals, and the third and fourth as stamens.
5. Select the correct answer: Based on the analysis, the structure of the flower would be 'petal-petal-stamen-stamen', which corresponds to option b.

Key Concepts

ABC Hypothesis

The ABC hypothesis is a model that explains the genetic control of flower development. It posits that three classes of genes, labeled A, B, and C, interact in specific combinations to determine the identity of floral organs. Gene A is responsible for sepal formation, gene B for petal and stamen formation, and gene C for carpel formation. The expression of these genes in different whorls of the flower dictates the type of floral structures that will develop.

Whorls in Flower Structure

Flowers are typically organized into four concentric circles called whorls, each of which can develop into different floral organs. The outermost whorl is usually composed of sepals, followed by petals, stamens, and finally carpels at the center. Understanding the arrangement and function of these whorls is crucial for predicting the structure of a flower based on gene expression patterns.

Gene Expression Patterns

Gene expression patterns refer to the specific activation or suppression of genes in different parts of an organism. In the context of the ABC hypothesis, the expression of genes A, B, and C in various whorls determines which floral organs will form. For example, if gene B is expressed in all whorls, it suggests that petals and stamens will be present, influencing the overall structure of the flower.