College Level Bio Exam 3 - Evolution

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1. Explain why the ‘Misconceptions about evolutionary theory and processes’ given in Lecture 12 are misconceptions. (You should be able to do this before Exam 3, but you may not be able to do this after the first couple of evolution lectures)

• Evolution is a theory about the origin of life —> Evolution is the study of how life changes after origin, not where life comes from

• Evolution results in progress; organisms are always getting better thru evolution —> no because Nature Selection is a process, not a conscious decision maker. It has many different outcomes, such as a loss of certain traits.

• Individual organisms can evolve during a single lifespan —> They cannot evolve because genetic information is often fixed. Evolution is the process of change in a species overtime, so it would not be able to be measured in a singular individual.

• Humans are not currently evolving —> Evolution does not necessary stop, although humans do not evolve to the same degree as organisms in the wild

• Natural selection involves organisms trying to adapt —> no because adaptative traits occur through chance, like genetic mutations. Organisms are unable to generate traits just because they need it.

What is the Great Chain of Being?

All matter and life is arranged in a hierarchical structure planned and determined by god

Explain the important contributions to the development of evolutionary theory made by: Lamarck, Lyell, Malthus, & Charles Darwin.

• Lamark was the first person to propose that species could change overtime to become new species, believed they evolved thru inheritance of acquired characteristics and use and disuse

• Lyell was one of the first to believe the Earth was over 300 mill y/o, popularized uniformitarianism —> which argued that the actual age of earth allowed sufficient time for gradual change to occur in organisms.

• Malthus focused on human population growth and availability of resources, figuring out that population size is always greater than the amount of resources (creating competition)

• Charles Darwin defined evolution as descent with modification, proposed plausible mechanism to explain how descent with modification can occur, NS.

Explain the problems with Lamarck’s concept of how evolution occurs.

Lamark’s idea that evolution occurs when an organism begins to use an organ/feature more, it increases in efficiency or size over time.

Ex: Giraffee uses neck more often, causing it to grow more and its offspring would inherit the neck.

This is incorrect because traits acquired during an organism’s lifetime are not inherited by its offspring, as often this change only effects the phenotype rather than the actual genetic makeup that is to be passed down.

Explain the idea of Uniformitarianism and the role it played in shaping Darwin’s theory of evolution by natural selection.

Uniformitarianism is the belief that incremental changes created all of Earth’s geological features, the present is key to the past. Darwin recognized that if geological features could change overtime, so could life.

Explain what artificial selection is and the role it played in shaping Darwin’s theory of evolution by natural selection.

Artificial selection is humans consciously breeding for or against certain traits in organisms. Using AS, Darwin showed evolution and natural selection is possible, that maybe nature, like humans, could select for or against certain traits in a population.

Give examples of artificial selection.

The pigeons Darwin bred, or ancient carrots vs Modern carrots (or other fruits and veggies)

Did Darwin benefit from knowledge of Mendel’s work?

No

Define evolution (two definitions).

Darwin = descent with modification. Or the change of the genetic composition of a population over time.

What is the focus of evolutionary biology?

To understand how and why organisms change overtime, the history of life and the processes that lead to diversity in life

Explain the importance of Darwin’s Finches (the finches on the Galapagos Islands) in shaping Darwin’s theory of evolution by natural selection.

Darwin drew evidence from the finches, which had resembled the finches in mainland South America. Different species of different finches varied in beak size/shape, so Darwin thought these could have been modified from an original mainland ancestor, as if that ancestral finch colonized the island and diverged into different species.

What was Darwin’s major contribution to evolutionary thought

The proposition of a plausible mechanism to explain how evolution could occur —> NS

Describe natural selection, including the significance of the ‘struggle for existence’ and unequal reproduction

Natural selection is the process in which individuals with certain traits are more like than others to survive and reproduce because of those traits. The unequal reproduction occurs because of a struggle for existence, where there is a larger population than the amount of resources available, causing competition for resources and ability to survive.

Describe the 3 conditions/requirements necessary for natural selection to occur.

1. Variation: variation is needed for evolution, creating diff variants

2. Differential Reproductive success: certain diff variants need to have a higher chance at reproductive success

3. Heritability: the favorable trait needs to be heritable

Explain how the graphs presented in lecture (Galton/height & emu/femoral muscle) provide evidence for heritability and differential success respectively

• Height graph shows evidence for heritability because the graph showcases a positive correlation between the height of parents and the height of their children. Taller parents are more likely to produce taller children.

• Emu graph showcases differential reproductive success because the graph showcases a positive correlation between size of femoral muscle and the amount of children they have. Emus with larger sizes of femoral muscles are more likely to have more amounts of offspring

Explain the term ‘target of natural selection’

It is the heritable traits that, due to their effects on an organism’s survival and reproduction, become more or less common within a population over generations.

Define the term adaptation. Which mechanism of evolution causes adaptation

Adaptation is a heritable trait that improves an organism’s fitness and ability to survive, only occurs with NS

Explain the Medium Ground Finch example in detail. Explain how this illustrates adaptation and how it satisfies the requirements/criteria necessary for natural selection

Medium Ground Finches suffered long droughts that reduced the number of small seeds available to them. 85% died. Puncture vine plants survived, to which larger beaked birds had an easier time cracking the seeds in comparison to the smaller beaked individuals. This caused smaller beaked birds to die at higher rates, showcasing adaptation because the larger beak is an advantageous trait that increased the larger beaked birds fitness in comparison to the smaller beaks.

It has the conditions of NS because there is variety of beak sizes, and diff success since larger beaks were more likely to reproduce, and heritability as the beak size was heritable.

Explain why a variant of a trait that is favored by natural selection in a particular environment at a particular time may not be favored in other environments or at other times (illustrated by Medium Ground Finch)

Not everywhere in the world has the same exact environmental factors, meaning that certain traits that are more adaptive in colder weather such as thicker fur, are not adaptive in hotter environments, or adaptive traits that match fur color dark rock environments are not adaptive in lighter colored environments.

With the Medium Ground Finch, beak size consistently fluctuates as the environment alternates between periods of drought and wet periods.

Describe the 3 patterns of natural selection – directional selection, stabilizing selection, & disruptive selection. Give an example to illustrate each pattern

• Directional selection: NS favors individuals at one end of the phenotypic range —> ex: darker colored moths in soot of England’s industrial revolution

• Stabilizing selection: NS favors intermediate variants by acting against extreme phenotypes —> ex: robins lay 4 eggs cuz larger clutches may result in malnourished chicks while smaller clutches may result in no viable offspring.

• Disruptive selection: When NS favors both extremes of the phenotypic range over intermediate —> ex: African seedcrackers, large beaks are good at cracking hard seeds while small beaks are good for handling soft seeds, medium sized beaks are not efficient at either.

How does the rock pocket mouse example illustrate natural selection and adaptation

They showcase NS and adaptation because lighter colored mice are able to blend into sandy environments while darker mice are able to blend into darker rock, allowing for both of them to avoid visual predators and thus increases their fitness and ability to survive (adaptation). With NS, there is variation in fur, and diff success in respective environments, and heritability with the traits.

Define the term population. Why do we say that evolution occurs in populations and not in individuals

Population is a group of individuals of the same species living in the same geographical location at the same time, therefore being able to interbreed. We say it occurs in populations and not individuals because it occurs in populations overtime, acting on individuals and their certain traits. The effects of NS are only observable in populations over periods of time because it is based on the gene pool of them, which many individuals contribute to.

What does the term allele frequency mean? In a situation with a gene with two alleles, how do you calculate allele frequencies if you know the number of individuals that have each genotype

Allele frequency is the amount of times a certain allele appears in population’s gene pool. You can calculate it like proportions.

Define the term gene pool

Gene pool is the total of all genes in a population, all alleles carried by all individuals in a population at a certain time.

Describe the 4 forces (or 4 mechanisms) of evolution

1. Mutations: random changes in DNA sequencing

2. NS: process in which certain individuals with a certain inheritable trait are more likely to reproduce and survive than others

3. Genetic Drift: chance events causing changes in allele frequencies

4. Gene flow: movement of alleles in and out of a population due to movement of individuals or gametes.

Describe how each of the 4 forces of evolution affects genetic variation in a population

They all change allele frequency. Mutations are the ultimate source of new alleles, NS favors certain alleles, Genetic drift is when chance events change allele frequencies, and gene flow causes movement of gametes or individuals’s alleles in and out of a population, causing genetic variation in each population while making them more similar to each other.

Why is mutation considered a mechanism of evolution? Why is mutation so important in evolution

It is the ultimate source of new alleles, causing genetic variation which is needed in evolution.

Explain the term genetic drift. How does genetic drift affect genetic variation in a population

Genetic drift is when chance events that have nothing to do with adaptability change allele frequency in a population. It is more effective in smaller populations, and affects genetic variation because some alleles can go into fixation or disappear completely.

Are the effects of genetic drift greatest in small or large populations

Smaller

What is the fixation of an allele? How does genetic drift affect fixation

Alleles that go into fixation have the allele frequency of one. Genetic drift can make this possible by chance, leading to random alleles going into fixation as genetic variation is decreased.

How is it that genetic drift is a random process but the effects of genetic drift are predictable

It is statically predictable since since it causes less genetic variation and is more pronounced in smaller populations

Explain the term gene flow

It is the movement of alleles in and out of a population due to the movement of individuals and/or their gametes

How does gene flow relate to adaptation

Gene flow can introduce new alleles to a population with 2 diff outcomes. One where it can aid in adaptation or it can slow down adaptation. It also increases genetic diversity, something required for NS which can result in adaptations.

How does gene flow change the genetic makeup of a population (i.e., change the gene pool of a population) & thereby cause it to evolve

It can add diversity to a population by introducing new alleles to its gene pool, making it easier for NS to take place.

In terms of introducing new alleles to a population, how does gene flow differ from mutation

Mutations create new alleles while gene flow introduces already existing alleles to other populations

Does gene flow tend to make the gene pools of two populations more similar to one another or more different? Why

Makes them more similar to one another because now after gene flow occurs, they have alleles in common within their gene pool, making them more genetically similar to each other.

Use the example of the water snakes in Lake Erie to explain how gene flow and natural selection can sometimes act as opposing forces

The mainland snakes that are patterned are favored by NS, while island snakes that are plain are favored by NS. So, NS on the island actively gets rid of the pattern skin allele, but gene flow from mainland continuously reintroduces it, canceling out NS.

Be able to explain the benefits (and any tradeoffs) of the human adaptations discussed in class: big brains, loss of body hair, light or dark skin tone, bipedalism (less info given for this trait), & lactase persistence. Why did natural selection favor these traits in humans? Describe the evolutionary history of these adaptations as outlined in class (if we went over it), including the environmental factors that favored these traits

• Big brains: developed most during changing climates during history, larger size made it easier for higher level thinking, info storage, but trade offs are longer developmental time, and harder to give birth (bigger heads)

• Loss of body hair: makes it easier for humans to be active during the day, allows for sweating, hair only on scalp keeps brain cool to prevent overheating and decrease in function

• Bipdealism: More energy efficient, less sun exposure, free hands

• Skin tone: Dark is protective against high UVR environments to prevent folate which is necessary in DNA production from being damaged. Light skin is protective against low UVR, to allow more vitamin d3 to be absorbed for immunity and absorption of Ca to prevent rickets

• Lactase persistence: evolved in dairying populations due to culture practicing

Explain the genetic mechanism that underlies the lactase persistence phenotype

Lactase persistence is dominant, meaning only 1 high activity allele is needed to produce enough lactase

How did mutation, culture, and natural selection interact in the evolution of the lactase persistence phenotype

Lactase persistence is more common in traditionally pastoralist cultures, mutations that caused lactase persistence are favored byNS in these cultures, LP individuals in dairying culture could take advantage of a new protein source and water source. LP is unlikely to have occurred more frequently in any population but it was mainly favored by NS in a particular culture context.

What is the difference between elevation and latitude

Latitude is position of a place N or S of the equator, elevation is height above sea level

How have Tibetans adapted to high elevation environments (you don’t need to know details for this example)? How is this different from acclimating to high elevation

They have the EPAS1 gene that allows them to process O2 diff and survive lower O2 levels that can pose serious health risks for most others. This is diff from acclimating because it is temporary, by producing extra red blood cells, while Tibetans have a permanent gene that allows for them to get enough O2, showcasing adaptation.

Define the term sexual selection

A form of NS in which individuals with certain traits are more likely than other individuals to to obtain mates

Explain why traits that are favored by sexual selection are not necessarily beneficial to an organism’s survival. Give an actual example to illustrate this

There are trade offs to being attractive or adaptative, especially since larger and more elaborate displays or calls are attractive and make them stand out to their mates, which also make them stand out to predators.
For example: Tungara frogs vocalize to attract females, adding chucks to their voice to make it more complex. While this brings attention of females, it makes them more visible to bats that use echolocation.

Explain the example of ptarmigans and their plumage

Their traits favored by sexual selection are not necessarily beneficial to their survival because in the winter their white plumage helps them blend in with their environment, but the males have red on their eyes to stand out to their female counterparts, which in turn makes them stand out to predators as well.

Explain the example of Tungara frogs and their vocalizations.

Tungara frogs vocalize to attract females, adding chucks to their voice to make it more complex. While this brings attention of females, it makes them more visible to bats that use echolocation.

Be able to describe and recognize the types of traits that tend to be favored by sexual selection: colorful ornaments, complex mating signals

Mates with the largest, most colorful ornaments, or most complex mating signals are often attractive to females.

Explain the 'good genes' hypothesis

It is difficult to maintain elaborate ornaments or to perform complex signals/displays well or accuratelt. These are a sign of ‘good genes’ (ex: no inherited genetic diseases, etc). It is an indirect way to assess the genetic condition of a potential mate and assess non-genetic health problems cuz its too difficult to fake.

Explain the term convergent evolution. Provide a few examples of convergent evolution (be familiar with examples of convergence given in class)

It is where different species and/or populations develop similar traits independent to one another.

Ex: Humans with lactase persistence. Independent mutations caused lactase persistence in diff populations

Explain how the rock pocket mouse example illustrates convergent evolution

The dark fur evolved independently in each population as they adapted to dark lava rock, not because they came from a common ancestor. It was a independent mutation that occurred by chance in the populations at diff locations.

Explain how the lactase persistence condition in humans illustrates convergent evolution

Humans with lactase persistence. Independent mutations caused lactase persistence in diff populations

Explain how light skin in Europeans and in northern Asians illustrates convergent evolution

Europeans and Northern Asians lived in similar UVR level environments, where it was low and ran the risk of a lack of vitamin d3 production or lack of Ca absorption. So they both ended up with the trait of lighter skin not because they came from a common ancestor, but because their environments had the same demands.

Explain why traits that evolve due to convergent evolution are usually adaptations

They are usually adaptations because convergent evolution means when diff species or populations face similar problems in their environment and evolve similar traits that improve fitness, the exact definition of an adaptation.

Describe the difference between homologous traits and analogous traits. Give actual examples to support your description

Homologous traits come from divergent evolution, where the traits have similar internal structure but maybe different functions, coming from a common ancestor. —> ex: human arm, bat wing, and whale flipper, they all have different functions but similar internal structure inherited from a common vertebrae ancestor.

Analogous traits come from convergent evolution, where traits evolve independently from each other but have similar functions, with most often different internal structures. —> ex: bird wing and fruit fly wing, they both have same functions but diff internal structure because they developed these traits due to demands from their environments that required for them to both fly.

What is the Biological Species Concept

Species are groups of interbreeding natural populations that are reproductively isolated from other such groups

Define the term reproductive isolation

The inability of different species to interbreed successfully and produce viable, fertile offspring. It cuts off gene flow, allowing for populations to diverge.

Why is reproductive isolation necessary for two populations to become two different species

It is necessary because gene flow is cut off, the way populations are able to maintain genetically similar. When cut off, populations will continue to breed, slowly developing genetic and phenotypic differences from diverging and not consistently sharing alleles in the gene pool.

Define the term speciation

Process in which new species form when a group within the species develop unique characteristics from the rest of the species. When gene flow is cut off, populations evolve independently of each other, developing 2 diff gene pools.

What are prezygotic barriers and postzygotic barriers to reproduction

• pre: biological features that prevent interbreeding with other species, prevents formation of zygote.

• post: reproductive barriers that prevents hybrid zygotes by 2 diff species from developing into viable, fertile adults

What are the four types of prezygotic barrier? Give examples of each (you should know the examples from class)

• Habitat isolation: Oak titmice live in oak woodlands, juniper titmice live in juniper woodlands

• Temporal: American toads mate in early summer, Fowler’s toads mate in late summer

• Mechanical: damselfly penises are a certain shape

• Behavioral: Mice are attracted to urine of their own species, songbirds use different mating calls and only respond to the calls of their own species.

What are the two types of postzygotic barrier? Give examples of each (you should know the examples from class)

• hybrid sterility: mule is viable but sterile cuz donkey has 62 chromosomes while horse has 64, so mule has 63=sterile

• hybrid inviability: crossing of a sheep and a goat do not survive

Define the term allopatry

geographical isolation, preventing gene flow between populations and thus allowing for species to diverge

Describe two ways that a population could become allopatric

1. Geographical barrier arises in an existing population

2. Part of a population colonizes new area isolated from original population

Why does allopatry facilitate different populations becoming different species? I.e., what is so important about allopatry?

Allopatry prevents gene flow between populations, allowing them to diverge independently and accumulate diff genetic and phenotypic adaptations over time. The genetic isolation develops reproductive barriers, eventually making separate species.

What are the three steps of the allopatric speciation model

1. populations isolated in diff areas evolve differences

2. differences become great enough to cause reproductive isolation (they affect mate choice)

3. when populations come back into geographical contact, they no longer interbreed

Does allopatry on its own cause speciation?

No, allopatry cuts off gene flow between populations, providing context within which reproductive barriers are most likely to evolve between populations.

Explain the examples that we used in class to illustrate allopatric speciation

The formation of the grand canyon created two geographically isolated (allopatric) populations of the antelope squirrel on the N and S sides of the canyon. Harris’ antelope squirrel vs white-tailed antelope squirrel.

Explain how the Drosophila experiment illustrates allopatric speciation

Flies from one population were split into 2 separate populations with different food sources. After many generations, flies raised on starch digested it better while flies raised on maltose digested maltose better, leading to evolution into “distinct species” that have different abilities.

Why have humans never split into multiple species

Humans are highly mobile, having interbred across vast geographical regions making it harder for us to be isolated. Also humans have a relatively small amount of genetic variation compared to other species.