Natural Selection - AP Biology

Balancing selection is a type of natural selection that maintains genetic variation in a population, making it the opposite of purifying selection. Examples of balancing selection include heterozygote selection, in which there is adaptive value for heterozygotes of an allele.

Natural selection is defined as survival and reproduction based on a specific phenotype. Phenotypes that increase reproductive fitness are “selected for” on different levels. Natural selection can take place on different levels of biological organization including gene, individual, and group levels.

Frequency-dependent selection is a type of natural selection in which the fitness of a phenotype depends on frequency. This includes positive frequency-dependent selection—fitness of a phenotype increases when it is common—and negative frequency-dependent selection—fitness of a phenotype decreases when it is common.

Darwin described his theory as "descent with modification," meaning that offspring inherit their genetic material from their parents, but with slight modifications. Darwin proposed that those slight modifications which provided a fitness benefit (made it more likely that an organism would reproduce) were more likely to be passed on.

Homeostasis is the tendency of the body to maintain stable, constant states. Homeostasis is often mediated by negative feedback systems, which prevent the measure from getting too high or too low. Regulation of body temperature within a narrow range would be an example of homeostatic regulation. Other examples include blood glucose concentration and blood calcium concentration.

Metabolism refers to the chemical processes of the body. These processes can help maintain homeostasis, but are not directly responsible for body regulation.

The r-selection strategy for reproduction is typically seen in environments that are very volatile and unpredicatable. It has a variety of characteristics including high brood sizes with a high mortality rate, and fast maturation with very little parental assistance. Low brood sizes are typically seen in the k-selection strategy for reproduction.

While natural selection is often described as "survival of the fittest," this explanation is not completely accurate. It paints the picture that the most fit individual lives the longest, when the real premise is that the individual with the most benefical combination of genes suited to the current environment reproduces more, thus passing on more genetic information to the next generation.

Biological fitness is directly related to the ability of an organism to survive and produce future progeny. There are a lot of factors that will play into an organism's fitness, especially in a harsh place like the tundra. Small size can be beneficial, as smaller animals require less food and can survive better in harsh environments, but large size can be beneficial to help preserve body heat. The color of an animal will help it to hide from predators; many tundra animals are white to help them blend in to the snow. Thermoregulation is extremely important in a cold environment; endotherms are able to regulate their own internal temperature, and will survive better than exotherms, which would be affected by the cold temperature of the air. Finally, fur and feathers help to trap body heat close to the skin and would enhance the fitness of animals in a cold environment.

Size, color, mode of thermoregulation, and fur all impact an animal's ability to survive in the tundra. Nocturnal activity, however, would not necessarily be favored over diurnal activity, as there is no clear advantage of one over the other in this specific environment.

With regard to evolution and natural selection, fitness refers only to the ability of an organism to contribute to the next generation of its species. In other words, if an organism has a large number of viable offspring, its fitness is high, regardless of other factors like strength, size, and longevity.

Of these answer choices, the only organism with an above-average number of healthy, surviving offspring is the prairie dog. The mule and the dog have below-average fitness because they cannot give birth. The turtle also has below-average fitness because it produces an unusually low number of healthy offspring. The human male has average to below-average fitness; certain traits made him choose not to produce offspring, though he may have been able to produce numerous offspring.

Innate behavior is known as inflexible behavior, in which learning plays no role in the behavior. Communicating, courtship, and decision making all rely on learned behavior from the environment.

The most biologically fit organism is one that produces the most fertile offspring. Lifespan can correlate to the number of offspring produced, but is not a direct factor in determining fitness.

Since the organism that lives 36 years produced the most offspring (6), it is the most biologically fit.

In evolutionary terms, “fitness” refers to the reproductive success or reproductive potential of an organism—its contribution to its species' gene pool.

Batesian mimicry involves a harmless species mimicking an unpalatable or harmful species, such as the butterfly in the example. Mullerian mimicry involves two unpalatable or harmful species resembling each other. This also helps predators learn which types of species to avoid. Cryptic coloration is more simply known as camouflage. Aposematic coloration is warning coloration, such as bright colors on poisonous tree frogs or venomous snakes.

According to Darwin's theory, the survival and reproduction of individuals is not random. Survival and reproduction is tied to the variations among individuals. Those with the most favorable variations are more fit; therefore, they are naturally selected.

A sharp decrease in population size caused by environmental or human impact is known as the bottleneck effect, where the bottlenecking occurs in the relative population diversity. This is mainly due to the fact that the individuals who survived rarely represent the genetic makeup of the initial population as a whole. The effect size is a statistical measurement of the strength of a phenomenon, which can be applied in the study of population dynamics, but is not a type of genetic drift. Artificial selection is the deliberate selection of mating preferences by humans in order to alter the proportion of traits in the offspring. However, this type of selection is not caused by a dramatic event, nor does it result in a severe decrease in population size. The founder effect does pertain to small populations but specifically on how genetic variation is lost in a small population that comes from a larger population due to misrepresentation.

In order for natural selection to take place, members of a population must have different biological fitnesses (a measure of how likely it is that an individual will pass on its genes through reproduction). Different biological fitnesses are a result of different phenotypes. Organisms with phenotypes better suited to their environments will have a higher fitness.

Natural selection does not require sexual dimorphism or competition between populations. Adaptation to environmental niches can result from natural selection over time.

Selection pressures is the correct answer here. A selection pressure is any factor that affects fertility or mortality, or anything that can cause a population to change genetically.

Initially, the population of bacteria was composed of mostly bacteria vulnerable to methicillin and a small number of resistant bacteria. Treatment with methicillin destroyed all of the vulnerable bacteria. leaving only the resistant alive to reproduce. Over time, the resistant bacteria became the majority.

Although it's possible a new patient could have introduced the first resistant bacteria, it's unlikely to have occurred in such a short time frame.

It's also unlikely the bacteria possessed the ability to resist the bacteria from the start, as methicillin treatment wouldn't have worked on any of them.

Bacteria do not possess a mechanism by which they can build up immunity to antibiotics over time.

This would be equivalent to the number of “grandchildren” produced by the organism. Biological fitness is defined by how capable the organism is of increasing the frequency of its own alleles. While individuals that consume more food grow larger, or have more mates than other members of their species are clearly thriving in their environment, which does not always mean that they produce more offspring. Also, it is possible that an organism could produce a large number of offspring that are infertile, which would ultimately not increase the frequency of its alleles. Therefore, the best determination of an organism’s fitness is the production of offspring that are themselves able to successfully produce offspring.