Question

Which of the following characteristics would not qualify an animal as a model organism? a. It has rapid development. b. It has a small adult size. c. It has a rapid life cycle. d. It has unique genes and unusual cells. e. It is easy to raise in the laboratory.

Short answer

Characteristic d: It has unique genes and unusual cells.

Step-by-step solution

Understanding the Concept of a Model Organism

Model organisms are species that are extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are chosen for their ease of maintenance in a laboratory setting, genetic tractability, and a fast life cycle.

Analyzing the Given Characteristics

Characteristics a, b, c, and e all enhance the practicality and applicability of an organism for laboratory study. These characteristics allow for rapid generation of data and the ability to maintain a manageable population for study.

Identifying the Non-Qualifying Characteristic

Characteristic d, having unique genes and unusual cells, would not qualify an animal as a good model organism. Model organisms typically have genetic and cellular features that are representative of a larger group of organisms. Unique genes and unusual cells would make it difficult for research on the model organism to be broadly applicable to other species.

Key concepts

Genetic Tractability

One of the hallmark traits of a model organism is its genetic tractability. This refers to the ability of researchers to easily manipulate an organism's genetic makeup to study gene function, interaction, and expression patterns.

In practice, genetic tractability means that the organism's genome is well-mapped, and tools such as CRISPR or gene knockouts are readily applicable. For example, the fruit fly, Drosophila melanogaster, has been a favourite amongst geneticists, largely due to its relatively simple genetic structure and the ease with which genes can be modified.

Enhancing the power of genetic modification, many of these model organisms have short generation times, enabling scientists to observe the effects of genetic changes over multiple generations in a short period. This is crucial for studies involving evolutionary biology or genetics, where observing the inheritance of traits is of interest.

Additionally, genetic tractability in model organisms extends to the ability to create transgenic lines—organisms that carry a gene from a different species. This has wide applications in medicine, agriculture, and basic science.

Laboratory Study Organisms

Model organisms must also be conducive to laboratory life. This requires them to have certain characteristics that facilitate their maintenance and breeding under controlled conditions. These include rapid development and a quick life cycle, which enable scientists to work through experimental cycles swiftly, and a small adult size, which allows for the management of large populations in limited space.

The laboratory environment itself must be amenable to the needs of these organisms, providing appropriate conditions for their growth and reproduction. Nutrient-rich growth mediums for microbes, temperature-controlled environments for temperature-sensitive organisms like the roundworm Caenorhabditis elegans, and plenty of space for organisms like mice, that exhibit complex behaviors, are all examples of laboratory adaptations for different model organisms.

A critical aspect of these laboratory study organisms is the consistency and uniformity of the conditions provided, ensuring that any observed biological variations are due to genetic differences or experimental manipulations and not environmental variability.

Biological Research Models

Lastly, model organisms serve as biological research models because they provide insights that are applicable to other organisms, especially humans. This is possible because of the concept of biological universality, which posits that fundamental processes like cell division, genetic inheritance, and metabolism are conserved across diverse forms of life.

As such, a model organism must have genetic and cellular systems analogous to those found in more complex organisms. Therefore, despite the versatility and convenience of model organisms, if their genes and cells are too unique, as in option 'd' of the exercise, they become less valuable as comparative models.

An exemplary biological model is the laboratory mouse, Mus musculus, which shares a significant amount of its genetic makeup with humans, making it exceptionally valuable for studying human diseases. The discoveries made in mice have often translated directly into understanding human biology, demonstrating the power of these biological research models in advancing science and medicine.