1.6 Genetic Mutations and Adaptability of Organisms

Natural Selection

Key to the theory of evolution by natural selection are new trait variations that arise spontaneously and make an organism more competitive in the struggle for survival. Following publication of Darwin's On the Origin of Species, in 1859, field stations were established where scientists could study the unique characteristics of organisms that had evolved to inhabit different environments. However, field observation could not explain the origin of variation or how new traits are inherited. The new sub-discipline of experimental evolution emerged at the turn of the 20th century with the goal to recreate evolution in controlled experiments with agricultural plants and animals. It soon became clear that mutations in genes are the source of variation and that Mendelian genetics offered a statistical method for analyzing the inheritance of new mutations. For centuries, farmers have chosen the animals they wanted to breed with each other. By selecting breeding pairs over many generations, farmers can be sure all of their animals have desired traits. Horses can be bred for strength, cows for milk production, and so on. This is the most widely used reproductive method in agriculture.

If you own a dog, it's likely he or she is a result of selective breeding. Dogs today are bred for traits that humans find desirable. These traits include herding ability, good temperament, size or appearance.

 

Photo source: Pip Breckon, Adrian Hill, Bev Carstensen.

Genetic Diversity and Adaptability

In sexual reproduction, offspring have unique combinations of genes (half from each parent). This creates variation in a population, because every individual is a little different from all the others.

Variation is very important to the survival of a species. The greater the diversity, the more likely it is that a species can adapt to change. Perhaps not all individuals will survive whatever change may occur, but at least some will! Why do some members of a species survive, but not others? In a way, the survivors have won a “genetic lottery.” Their genes happened to give them a lucky advantage that matched the conditions of change that occurred. Because they're still around to reproduce, their traits will be passed on to their offspring.

However, if a population gets too small, genetic diversity can be permanently lost. Read the Case Study on Cheetah, on the next page, for an example of this situation.

A Case Study in Genetic Diversity- The Cheetah

We'll use cheetahs as an example to help you understand the importance of genetic diversity in a population. The cheetah has been called the “poster child” for genetic diversity. After you read the following case study, you might see why.

Instructions

Read the Case Study, and then answer the questions that follow.

Image and article adapted from Genetic Diversity courtesy of Cheetah Conservation Fund 20,000 years ago, cheetahs lived in Africa, Asia, Europe and North America. About 10,000 years ago, all but one species of cheetah became extinct. This population decline forced close relatives to breed. As a result, the cheetah became genetically inbred. Inbred animals suffer from a lack of genetic diversity. As cheetah populations continue to decline, there is less and less genetic diversity in the species. Genes store inherited genetic information. Even though they may determine the same trait, each gene is different in every individual. By studying genetic diversity, scientists can figure out how animals in a population are related. This helps them predict how changes may affect the population. Cheetahs have much lower genetic diversity than other cats. This can cause lowered resistance to disease. Viruses that might affect one cheetah could be deadly to every cheetah. Other species are more diverse, so some individuals will naturally be more resistant to a virus. Since all cheetahs have a low genetic diversity, the virus could affect them all equally.

Genetically Modified Organisms (GMOs)

If you were to enter the Internet search term “GMO,” you would instantly find millions of sources of information. Try it now—how many results did you get? Debate continues about whether genetically modified foods should be labelled. You can imagine, for example, that an environmentalist would have different ideas about GMOs than a research company hoping to profit from selling them!

Genetically modified organisms contain altered genes. Their genes are altered on purpose with the goal of producing foods (mostly fruits and vegetables) with desirable traits.

One common way to produce a GMO is to use recombinant DNA technology. This means that DNA from two or more species are combined.

Adding foreign genes to plant DNA can improve crops in a number of ways:

• resistance to insects and disease

• improved flavour or appearance

• longer shelf life

• higher crop yields, allowing farmers to grow more food on less land.

Some concerns about GMOs are based on:

• health and safety

• economics

• ethics.

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