Describe natural selection and give an example of natural selection at work in a population.

1. The process in which genes flow from one population to another. The beak size of Darwin’s finches changing as the availability of different-sized seeds changes.
2. The process in which genes flow from one population to another. The founder effect occurring among humans immigrating to a new country.
3. The process in which better-adapted organisms are able to survive and reproduce; The beak size of Darwin’s finches changing as the availability of different-sized seeds changes.
4. The process in which better-adapted organisms are able to survive and reproduce; The founder effect occurring among humans immigrating to a new country.

1. You would expect 300 homozygous dominant blue flowers, 300 heterozygous blue flowers, and 200 homozygous recessive red flowers.
2. You would expect 200 homozygous dominant blue flowers, 400 heterozygous blue flowers, and 200 homozygous recessive red flowers.
3. You would expect 100 homozygous dominant red flowers, 100 heterozygous red flowers, and 600 homozygous recessive blue flowers.
4. You would expect 14 homozygous dominant red flowers, 186 heterozygous blue flowers, and 600 homozygous recessive blue flowers.

1. New traits appear through gene mutations or through genetic drift. In order to reach a steady, high frequency in the population, there must be many mutagens, such as UV radiation, in the environment to produce many mutations.
2. New traits appear through gene mutations or through genetic drift. In order to reach a steady, high frequency in the population, there must be a consistent source of immigrant individuals with the allele.
3. New traits appear through gene mutations or through evolution. In order to reach a steady, high frequency in the population, the allele must code for a favorable adaptation.
4. New traits appear through gene mutations or through gene flow. In order to reach a steady, high frequency in the population, the trait associated with the gene must be favored by either natural or sexual selection.

1. Population variation is a description of the diversity of different forms of life. An example of population variation would be the different forms and functions of prokaryotes versus eukaryotes.
2. Population variation is the geographic distribution of different phenotypes in a population. An example of population variation would be the fact that warm-blooded mammals that live near the poles tend to be larger than their southern counterparts to conserve heat.
3. Population variation is the distribution of phenotypes in a population. An example of population variation would be the many different fur colors and patterns found in domestic dogs.
4. Population variation is the distribution of genotypes in a population. An example of population variation would be Mendel’s pea plants that were homozygous dominant, heterozygous and homozygous recessive for various traits.

1. A breeder would not allow close relatives to mate because inbreeding increases the likelihood of fatal mutations in offspring.
2. A breeder would not allow close relatives to mate because inbreeding prevents gene flow which can bring new, successful genes into the population.
3. A breeder would not allow close relatives to mate because inbreeding causes diversifying selection, which dilutes the breeder’s desired genes in the population.
4. A breeder would not allow close relatives to mate because inbreeding can bring together deleterious recessive mutations that can cause abnormalities and susceptibility to disease.

1. The founder effect is an event that isolates part of a population, generating an allele frequency which is not typical of the original population. An example of the founder effect is the Amish population. The Amish population was established from about 200 German immigrants. Individuals of this founding population carried gene mutations that cause inherited disorders such as Ellis-van Creveld syndrome. This form of dwarfism is found in a large concentration in the Amish population today because the immigrants that established the population had a high concentration of the disorder in a very small population.
2. The founder effect is an event that kills off a significant proportion of a population, generating an allele frequency which is not typical of the original population. An example of the founder effect is the Northern elephant seal. At one point, hunting of these seals had reduced their numbers to less than 50 individuals. The population has since rebounded, but still contains less genetic variation than the related Southern elephant seal due to the loss of some alleles.
3. The founder effect is when only a few males within a population are selected by females to reproduce, generating an allele frequency which is different from the original population. An example of the founder effect is the reproductive pattern of mountain gorillas. Mountain gorillas tend to have a single dominant male, the silverback, who gets the vast majority of the matings in the population. This leads to the next generation expressing mainly genes from the silverback and very few genes from the other males, changing the genetic structure of the population.
4. The founder effect occurs when the selective pressure on a trait varies depending on the alleles expressed within the population, generating varying allele frequencies based on the genetic makeup of the original population. An example of the founder effect is the cyclical dominance of three throat-color patterns in side-blotched lizards.

Explain what a cline is and identify an example.

1. A cline is a type of geographic variation that is seen in populations of a given species that vary gradually across an ecological gradient. For example, endothermic animals tend to have larger bodies in the cooler climates closer to Earth’s poles, allowing them to better conserve heat.
2. A cline is a change in ecological conditions over a geographic distance. For example, a latitudinal cline is the decrease in temperature towards Earth’s poles, and an altitudinal cline is the decrease in temperature with increase in altitude.
3. A cline is the specific set of traits in a population of a given species that have been influenced by the local environment. For example, a population of warm-blooded animals that lived in a cooler climate closer to the North Pole would have larger bodies, allowing them to better conserve heat.
4. A cline is the specific set of ecological conditions in a geographic region. For example, towards the North Pole it is cold and there is little precipitation. This will influence the traits of the organisms that live there.

The large alpha male elephant seal is constantly fending off the advances of medium-sized males. Small males are then able to sneak copulation with females and successfully pass on their genes. What is this an example of? Explain.

1. This is an example of sexual selection. The females are selecting the small males over the large male.
2. This is an example of genetic drift. Because there are so many medium-sized males to compete with the large alpha male, the small males are able to mate and cause the gene pool to shift towards smaller individuals.
3. This is an example of positive frequency-dependent selection, which is selection that favors phenotypes that are either common or rare. The sneaky males (rare) are favored in this case.
4. This is an eample of directional selection. Because only the smallest males are mating, the next generation will have a higher proportion of alleles for small size, making the seals smaller over time.

Explain why there is no perfect organism despite natural selection.

1. because natural selection works on a geographic level
2. because natural selection works in a random manner like mutations
3. because of limitations due to a population’s existing variation in genes
4. because natural selection is limited to sexual dimorphism