When you look at a population of animals you may notice some variations or differences between individuals of the same species. Perhaps some are larger than others or there are differences in their coloration. These variations serve as the basis for natural selection where beneficial traits in a population that positively affect survival and reproduction will be preserved. For example, animals that can more easily camouflage with their environment evade predators and pass on their genes more often than those that do not. This camouflage coloration is a phenotype, defined as the visual expression of a trait. A genotype refers to the set of genes responsible for a phenotype. Therefore, due to natural selection certain genotypes are maintained over time, while less favorable variations disappear and this drives the evolution of populations.
We humans have studied this process and taken advantage of naturally occurring variations to purposely evolve plants and animals to farm or keep as companions. This process is known as artificial selection, the propagation and domestication of plants and animals for favorable traits. Let's look at dogs for example. Thousands of years ago, humans started selectively breeding pairs of wolves for traits like docility, protection and hunting prowess along with appearance. We continued this selective breeding over countless generations and this has culminated in scores of modern dog breeds, including the Great Dane and Chihuahua, which in turn are both very different in appearance and character to their ancestor, the wolf.
We have also implemented artificial selection in plants. Brassica oleracea was once a large, leafy plant, but it has been artificially selected in different ways to produce many common vegetables we eat today, including kale, cabbage, cauliflower and even kohlrabi. Another species in the same family, Brassica napus, is commonly known as the oilseed rape plant because of the abundant oil sequestered in its seeds, which are excellent for cooking or fuel production.
In this lab, you will artificially select traits from individual oil seed rape plants to produce two lines displaying different levels of a trait, hairiness.
At the end of this lab, students should know...
What is natural selection?
Natural selection describes the process where variations in traits differentially affect survival and reproductive success between individuals in natural settings.
What is required for natural selection to occur?
For natural selection to occur, phenotypes in a population must be variable, heritable, and result in variation in fitness of organisms.
How does natural selection lead to evolution?
Populations of a species contain genetic variations that are passed down among generations. These differences allow certain individuals to fare better in survival and/or reproduction.
What is artificial selection?
By adapting the concept of natural selection, humans have created a variety of domesticated plants and animals by selecting favorable traits.
How have we benefited from artificial selection?
Many of the crops and domesticated animals we keep today are an outcome of artificial selection. Artificial selection has enabled us to produce crops and animals more efficiently.
- Observing Artificial Selection in Plants
- Two weeks before beginning the pollination experiments, collect a sufficient amount of small pots with a drainage hole in the bottom of each pot.
- Fill each pot about halfway with moist potting soil. NOTE: It is recommended to use a minimum of 50 plants for generation one. It is standard practice to list the species name and date of planting on each individual pot, although this is not necessary to label the generation one plants.
- Add a fertilizer pellet to the surface of the soil and then add more soil to the pot, enough to cover the pellet.
- Use a dissecting probe to make a shallow ¼ inch depression in the surface of the soil.
- Then, touch a toothpick tip to a glue stick. Use the sticky end of the toothpick to pick up one of the Brassica seeds and place the seed into the depression in the soil. NOTE: The dissecting probe can be used to knock the seed off the toothpick as needed.
- Lightly cover the seed with a thin later of soil. Then, repeat steps 3 – 6 for each pot.
- Place the pots in a brightly lit area, such as near a south-facing window or under a grow light. NOTE: Ensure the light is uniformly distributed across the group of plans. If this is not possible, rotate the plants every few days to ensure equal exposure.
- Water the plants with a plastic dropper until a small amount drains out of the pot. Do this as frequently as necessary to keep the soil moist.
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