Question

What is a homeotic mutant? a. an individual with a structure located in the wrong place b. an individual with an abnormal head-to-tail axis c. an individual that is missing segments d. An individual with double the normal number of structures

Short answer

a. an individual with a structure located in the wrong place

Step-by-step solution

Definition of Homeotic Mutant

A homeotic mutant is an individual organism with abnormalities in the expression of homeotic genes, leading to altered body plans or structures. The correct option should describe an organism where the usual body structures are misplaced or replaced.

Analyzing the Options

We will now analyze the options given and find the one that correctly describes a homeotic mutant. a. An individual with a structure located in the wrong place b. An individual with an abnormal head-to-tail axis c. An individual that is missing segments d. An individual with double the normal number of structures

Selecting the Correct Option

The correct answer is Option A, as it describes an organism with a structure located in the wrong place, which is a characteristic of homeotic mutants. The other options may describe an organism with developmental abnormalities, but not specifically a homeotic mutant.

Key concepts

Homeotic Genes

Homeotic genes are an essential group of genes that determine the anatomical structures that will arise in a specific part of an organism during embryonic development. Think of them as master control genes—they tell cells what they should become as an organism develops from a single cell into a complex being with multiple different tissues and organs.

When homeotic genes are functioning normally, they ensure that proper structures grow where they are supposed to, like making sure that legs develop in the correct segment of an organism, or that antennae grow on the head rather than on the tail. However, when there is a mutation in one of these genes, it can lead to dramatic and sometimes bizarre shape changes, resulting in what are known as homeotic mutants.

An example of homeotic genes at work can be found in the fruit fly Drosophila melanogaster, where the Antennapedia complex is responsible for specifying the identity of the segments that make up the fly's head and thorax. A mutation in these genes can cause, for instance, a leg to grow where an antenna should be.

Genetic Mutation

A genetic mutation refers to a change in the sequence of nucleotides in DNA. This can occur due to copying errors during cell division, exposure to radiation, certain chemicals, or viruses, or can be inherited from a parent. Mutations can be beneficial, neutral, or harmful to an organism.

A mutation that occurs in the homeotic genes can be particularly impactful, as it disrupts the normal development plan of the organism. These mutations can be categorized into different types:

• Point mutations: a single nucleotide change.
• Insertions and deletions: addition or loss of nucleotides in the DNA sequence.
• Frameshift mutations: insertions or deletions that change the 'reading frame' of the gene.
• Chromosomal mutations: larger changes that affect whole sections of a chromosome or entire chromosomes.

Whether a mutation will manifest as a noticeable trait or have subtle effects depends on its nature and the gene affected. In developmental biology, studying mutations in homeotic genes has been profoundly important for understanding how complex organisms are built from a simple set of instructions.

Developmental Biology

Developmental biology is the study of how organisms grow and develop from fertilization to adulthood. This branch of biology seeks to understand how a complex organism arises from a relatively simple, single-celled zygote. The development process encompasses cell division, differentiation where cells become specialized for specific functions, morphogenesis (the process that gives rise to the shape of an organism), and growth.

Homeotic genes play a pivotal role in this grand orchestration. They provide the molecular cues that guide the developmental process, ensuring that each part of an organism is made at the right time and place. Understanding how these genes work and how they can be modified by genetic mutation is key to deciphering the complexity of life.

In light of many heritable diseases or birth defects, developmental biology not only aims at answering fundamental questions about life but also holds potential for therapeutic advances. For instance, by comprehending how homeotic gene mutations lead to structural misplacements in homeotic mutants, researchers can develop strategies to correct or compensate for these defects.