Problem 12 - Biology

Question

According to the ABC model of floral organ development in Arabidopsis, the A gene is needed to specify sepals, the A and B genes to specify petals, the \(\mathrm{B}\) and \(\mathrm{C}\) genes to specify stamens, and the C gene to specify the pistil. If a mutation occurs in one of the B genes, rendering it inactive, the resulting flowers will consist of (a) sepals, petals, stamens, and pistils, (b) sepals, stamens, and pistils (c) petals, stamens, and pistils (d) sepals and pistils (e) petals and stamens

Step-by-Step Solution

Answer

The resulting flowers will consist of sepals and pistils (d).

Step 1: Understand the ABC Model

The ABC model is a theory that explains the development of floral organs through the interaction of three classes of genes: A, B, and C. Sepals are formed by the presence of A genes alone, petals by both A and B genes, stamens by both B and C genes, and pistils by C genes alone.

Step 2: Identify the Effects of a Mutation in Gene B

A mutation in the B genes means that any floral organ requiring B for its development would be affected. In this scenario, petals, which require both A and B, cannot form. Similarly, stamens, which need B and C, cannot form either.

Step 3: Determine the Remaining Floral Organs

With the B gene inactive, only the organs that do not require B can form. This leaves sepals, which require only A, and pistils, which are formed with C alone.

Step 4: Choose the Correct Option

According to the ABC model and the effect of the B gene mutation, the correct composition of the resulting flower is sepals and pistils only.

Key Concepts

Arabidopsis

Arabidopsis thaliana is a small flowering plant that's widely used in genetic and plant biology research. It's often considered a model organism due to its simplicity and the extensive genetic knowledge already available.
Its genome is completely sequenced, which means researchers can easily study the effects of gene mutations and observe changes.
This is particularly useful when investigating floral organ development such as sepals, petals, stamens, and pistils, which are all influenced by different genes within Arabidopsis.

Gene Mutation

Gene mutation refers to changes in the sequence of DNA in an organism's genome. In the context of the ABC model of floral development, mutations can highly impact the structure and appearance of the flower.
Different types of gene mutations exist, such as deletion, insertion, or substitution, and they can have a range of effects from benign to severe.
If a gene like the B gene in Arabidopsis is mutated, it can lead to the absence or alteration of floral structures that depend on that gene.
This is why understanding gene mutation is crucial for grasping how flowers develop and function.

Floral Organ Development

Floral organ development is a fascinating process guided by the interaction of specific genes. In the ABC model, three primary genes determine the identity of floral organs: A, B, and C.
Here's a quick breakdown of how each gene contributes:

• A gene: Specifies sepals
• A + B genes: Specify petals
• B + C genes: Specify stamens
• C gene: Specifies pistils

This gene interaction ensures that a flower develops all the necessary parts in the correct arrangement. If any of these gene interactions are disrupted by mutations, it can result in flowers missing some organs or having them in the wrong places.

Sepals and Pistils Formation

Sepals and pistils are two key components of a flower, each with distinct roles. Sepals are the outermost parts and usually serve as protection when the flower is in bud form.
In Arabidopsis, sepals develop due to the activation of the A gene alone. Pistils, on the other hand, are the female reproductive parts responsible for seed development.
The C gene is solely responsible for the formation of pistils.
In cases where there is a mutation in the B gene, which affects petals and stamens, the formation of sepals and pistils continues, as they do not rely on the B gene. Understanding this process helps in grasping how gene interactions result in the overall architecture of the flower.