test 4

Select ALL statements that correctly describe the mechanisms of microevolutionary change.

- A population's allele frequencies are always influenced to some degree by genetic drift. - Both mutations and gene flow can be important sources of new genetic diversity within a population. - Gene flow can cause rapid microevolutionary change. - Artificial selection can lead to traits that are harmful for an individual's ability to survive and reproduce. - Microevolutionary changes due to sexual selection are the result of heritable differences in mate preference and ability to compete for a mate

Select ALL statements that correctly explain why natural selection leads to organisms that are far from perfectly suited to their environment. - Adaptations are not necessarily beneficial under a wide range of environmental conditions. - Natural selection is limited by the genetic variation in a population. -Some adaptations are not heritable. - Natural selection can favor traits that decrease an individual's fitness in their current environment

- Adaptations are not necessarily beneficial under a wide range of environmental conditions. - Natural selection is limited by the genetic variation in a population. ***Limited genetic variation (i.e. the absence of particular heritable traits in a population) and fitness trade-offs (an inability to "maximize" everything) are among the factors that prevent natural selection from leading to perfect organisms. Another is that environmental conditions can change, either because the conditions in the area where a population lives changes or because individuals move to a different area where the environmental conditions are different.

Select ALL statements that correctly describe evolutionary change. - Evolution can change the allele frequencies in a population, but cannot alter an individual's allele frequencies. - Evolutionary change can act on traits that are not influenced by genes. - All mechanisms of evolutionary change increase the frequency of beneficial traits within a population. - The distributions of heritable phenotypes in a population can be affected by multiple mechanisms of evolution at the same time. - Heritable traits that are not beneficial for individuals in a population will eventually be eliminated by the mechanisms of evolutionary change.

- Evolution can change the allele frequencies in a population, but cannot alter an individual's allele frequencies. - The distributions of heritable phenotypes in a population can be affected by multiple mechanisms of evolution at the same time.

Which of the following explains how evolutionary change affects the allele frequencies and trait distributions in populations? T- he distribution of all traits within a population can be altered by evolutionary change, but the frequencies of some alleles cannot. - The frequencies of alleles within a population can be altered by evolutionary change, but the trait distributions cannot. - Evolutionary change alters either the allele frequencies or distribution of traits in a population, but cannot affect both at the same time. - Evolutionary change alters the frequencies of alleles within a population, which can be observed as changes in the distribution of traits.

- Evolutionary change alters the frequencies of alleles within a population, which can be observed as changes in the distribution of traits.

Which of the following correctly describe(s) evolutionary change? - Evolutionary change can only affect the distributions of traits that can be passed from generation to generation (heritable). - Evolutionary change cannot occur in a population in a single generation. - Evolutionary change can only alter the distributions of traits that improve an individual's ability to survive and reproduce.

- Evolutionary change can only affect the distributions of traits that can be passed from generation to generation (heritable).

Which of the scenarios below, if any, illustrate artificial selection?

- Farmers allow only certain turkeys to mate, and farm-raised turkeys have more white meat and grow faster than turkeys that live in the wild. ****Artificial selection is a change in allele frequencies due to humans choosing individuals with certain genetically determined traits as the parents of the next generation. Directly modifying genes and effects due to changing environmental conditions (by humans or as a result of natural causes) are NOT examples of artificial selection.

Select ALL statements that correctly describe genetic drift. - Genetic drift can affect the allele frequencies of populations that are also influenced by other mechanisms of microevolution. - Genetic drift can only alter the allele frequencies of small populations. - Genetic drift can cause evolutionary change in a single generation. - Genetic drift typically decreases genetic variation in populations where it significantly alters allele frequencies.

- Genetic drift can affect the allele frequencies of populations that are also influenced by other mechanisms of microevolution. - Genetic drift can cause evolutionary change in a single generation. - Genetic drift typically decreases genetic variation in populations where it significantly alters allele frequencies. ***Genetic drift is change due to random sampling of alleles. One scenario in which genetic drift can significantly alter allele frequencies within a population is a bottleneck - an event that leads to a significant decrease in the size of a population. An easy way to visualize this is to imagine a big jar of jelly beans with 50 different flavors (alleles) and many jelly beans of each flavor. If you grab a small handful (e.g. 12 jelly beans), the frequency of each flavor in your handful will be very different from the frequencies in the jar. Scenarios such as bottlenecks can cause significant change in the allele frequencies of a population in a single generation. Though small populations are more likely to be significantly affected by genetic drift, ALL populations are affected at ALL times to some degree simply due to random fertilization. Any populations' allele frequencies can be affected by multiple mechanisms of microevolutionary change at once (and most are). In populations where genetic drift causes significant change in allele frequencies (e.g. bottlenecks, small populations), the number of different alleles in the population is most likely to decrease. Fewer different alleles means that there is less genetic variation in the population.

When assessing microevolutionary changes, why is it important to consider both trait distributions and allele frequencies?

- The distribution of a particular heritable trait within a population could change without an alteration in allele frequencies. - Genetic differences (e.g. different alleles) do not always result in trait differences. - Some differences in traits are not due to genetic differences. **The relationship between an organism's genotype (combination of alleles) and its phenotype (combination of physical and functional traits) is complex. Some genetic differences do not lead to differences in traits. For example, two alleles could have different DNA sequences but result in the same polypeptide due to the redundancy of the genetic code. Additionally, most traits can also be influenced by the environment. This leads to differences in traits between individuals that are NOT heritable. Finally, the same allele frequency can lead to different trait frequencies (like the mouse population we used as an example in class). Therefore, it is possible for the distribution of a particular trait to change in a population WITHOUT changing the allele frequency. The reverse is also true - changes in allele frequencies may not affect phenotype frequencies.

In the context of evolution, genetic variation is important because - it gives individual organisms the ability to undergo evolutionary change during their lifetime. - it allows an individual to pass on only the most beneficial alleles to its offspring.it - provides a source of allele variation that may be beneficial if the environmental conditions change. - ensures that some individuals in a population will have the traits they need to survive.

- provides a source of allele variation that may be beneficial if the environmental conditions change. *** Mutations are an important source of new alleles in a population. In sexually reproducing organisms, variation introduced by crossing over, independent alignment of chromosomes, and random fertilization can also lead to new allele combinations that may affect phenotype frequencies. Although genetic variation introduced by mutations can be (and frequently is) harmful, some mutations introduce new alleles that are beneficial in the current or future environment. Individuals CANNOT evolve, and which alleles are passed on to the offspring of an individual is entirely random. Asexually reproducing organisms pass on ALL of their alleles. In sexually reproducing organisms, which alleles are passed on is due to the behavior of chromosomes in meiosis and random fertilization.

Which of the following correctly describe(s) adaptations?

A trait that is an adaptation may cease to be an adaptation if the environment changes *** Adaptations are traits that improve an individual's evolutionary fitness - their ability to pass their alleles on to the next generation. Survival is ONLY beneficial if it allows an individual to reproduce more and thus have more offspring. Whether or not a trait is an adaptation depends on the particular set of environmental conditions; if the conditions change, traits that increased an organism's fitness in the initial environmental conditions may no longer be beneficial. The terms "more adapted" and "less adapted" are not valid - evolution does not and cannot have a goal.