Problem 10 - Biology Today and Tomorrow with Physiology

Question

Banana plants produce seedless fruit because they are ___. a. triploid b. monocots c. propagated by grafting d. treated with colchicine.

Step-by-Step Solution

Answer

a. triploid

Step 1: Understanding the Question

The question asks why banana plants produce seedless fruit, presenting four choices: triploid, monocots, propagated by grafting, and treated with colchicine.

Step 2: Analyze Each Option

Let's analyze each option: - **Triploid**: A triploid organism possesses three sets of chromosomes, which often results in infertility or seedlessness, as seen with bananas. - **Monocots**: This term refers to one of the major groupings of flowering plants based on their seed structure, and not directly related to seedlessness. - **Propagated by grafting**: This is a method of plant propagation, not directly causing the absence of seeds. - **Treated with colchicine**: Colchicine is a chemical used to double chromosome numbers, leading to polyploidy, but it is not the direct reason for seedlessness in bananas.

Step 3: Eliminate Incorrect Options

By the analysis: - **Monocots** is eliminated because it refers to a group of plants rather than seedlessness. - **Propagated by grafting** is not a direct cause for seedlessness. - **Treated with colchicine** is related to polyploidy but not the direct reason specific to bananas.

Step 4: Confirm the Correct Answer

The best explanation for seedless bananas is that they are **triploid**. Triploid plants typically cannot produce viable seeds because the odd number of chromosome sets interrupts normal meiosis, leading to seedlessness.

Key Concepts

Polyploidy in Plants

Polyploidy refers to a condition where an organism possesses more than two complete sets of chromosomes. This phenomenon is particularly common in plants and can result from various processes, such as the fusion of unreduced gametes or the application of certain chemicals, like colchicine, which can cause chromosome doubling.
Polyploid plants can be categorized as:

• **Autopolyploids**: These arise from chromosome duplication within a single species, resulting in multiple homologous chromosome sets.
• **Allopolyploids**: These result from hybridization between different species, combining the chromosome sets from each parent.

Polyploidy often leads to significant changes in the plant's traits. These include increased size, enhanced stress resistance, and sometimes sterility, especially in odd ploidy levels, like triploidy. Polyploidy plays a crucial role in plant evolution and agriculture, offering a means to create new species with desirable characteristics.

Seedless Fruit

Seedless fruit, like those found in bananas and watermelons, is often a result of polyploidy. Specifically, triploid plants, which contain three sets of chromosomes, are typically sterile because they cannot undergo normal meiosis. This sterility prevents the production of viable seeds, resulting in seedless fruit.
There are several ways farmers can produce seedless fruits:

• **Breeding**: By crossing diploid (2n) and tetraploid (4n) plants, triploid (3n) offspring can be created, yielding seedless fruit.
• **Chemical Treatment**: Substances like colchicine are used to induce polyploidy, although this is not the typical method for bananas.

Seedless fruits are often preferred by consumers for convenience and taste. They are also commercially beneficial as they can enhance the market appeal of fruits.

Chromosome Sets in Plants

Chromosomes are structures within cells that contain DNA, the blueprint for plant development and functioning. The number of chromosome sets can drastically affect a plant's characteristics and reproductive ability.
Key terms include:

• **Haploid (n)**: A single set of chromosomes, typically found in gametes.
• **Diploid (2n)**: Two sets of chromosomes, one from each parent, which is the typical state for most plants.
• **Polyploid (3n, 4n, etc.)**: More than two sets of chromosomes, often resulting in modified traits and functionalities.

Having an odd number of chromosome sets, like in triploids, poses challenges during meiosis, which usually requires pairing of homologous chromosomes. This results in incomplete or irregular division, often leading to sterility and seedlessness. Therefore, understanding the chromosome sets is crucial in plant breeding and the agricultural sector for developing plants with specific desired traits.