Evolution Test 2
- How does population genetics differ from “traditional” genetics?
- Traditional genetics is concerned with finding out the possible genotypes of the offspring. Population genetics is concerned with finding the shift is allele frequency.
- What is the CCR5 gene and what is a Δ32 allele?
- The CCR5 gene codes for a protein on the HIV virus that acts as an attachment area for connection to white blood cells. The Δ32 indicates that 32 base pairs have been deleted from the functional gene sequence making the protein dysfunctional. Individuals who have two copies of this mutation have a much smaller chance of contracting HIV.
What are the two Hardy-Weinberg conclusions and why are they both needed?
- The allele frequencies will not change generation after generation. This shows that no evolution will take place under these conditions.
- If the allele frequencies in a population are given by p and q, the genotype frequencies will be given by p2, 2pq, q2. We can find and track these frequencies in the population
- If either of these principles do not hold then the population is evolving
- What use is the Hardy-Weinberg Equilibrium Principle?
- Allele and phenotype frequencies do not change in an ideal situation.
- What are the 5 crucial assumptions of the Hardy-Weinberg Equilibrium Principle?
- There is no selection
- There is no mutation
- There is no migration
- There are no chance events
- Mating is random
- Describe the ADH study and explain its relevance.
- ADH is an enzyme used by fruit flies to break down ethanol. They found an ADHF and ADHS They separated the flies into two groups, one with normal food and one enriched with ethanol. The normal group showed no significant change in the allele and genotype frequency but the enriched group showed a significant shift toward ADHF. This shows that the ADHF gene showed a significant advantage in the experiment and the flies with this gene was more fit for the environment.
- Why won’t CCR5- Δ32 allele increase in frequency?
- There is no population that has a high frequency of the allele coupled with a high rate of HIV which is the only scenario in which evolution would take place and we would see a shift. In addition, many people with this allele are heterozygotes and still can contract the virus and die without reproducing.
- Describe what type of alleles Natural Selection works most strongly on and explain why?
- Alleles that can be obviously selected are better for natural selection such as when one allele causes a deformity. These are examples of dominant and recessive alleles
- How does Dawson’s experiment demonstrate the concept referred to in question 1?
- Dawson used flour beetles colonies that had only heterozygotes in it and allowed them to breed. Individuals with ll died and so over several generations, the allele frequency of the dominant allele rose.
- Differentiate between overdominance and underdominance and give an example of when overdominance can occur.
- Overdominance is when a lethal allele is combined with the normal allele creating a heterozygote which has a higher fitness than a homozygote. Under dominance is when the homo has a higher fitness that the hetero. Over dominance can occur when the hetero has a reproductive advantage.
- Explain how frequency-dependant selection works
- The variation selected for is the most common until that becomes to abundant and then it switches
- Describe the potency of Mutation as an evolutionary force and explain why?
- Without mutation, there would be no variation. This is the ultimate source of evolution. Often mutation can be a good thing as it leads to a better functioning protein or so on.
- What happens when mutation is combined with selection and how does cystic fibrosis exemplify this?
- When mutation occurs, the population can begin to select for which allele is most fit for the environment and then the population can start to evolve toward the better allele and all the while new mutations are being created. Cystic Fibrosis follows this pattern. Parents generally have fewer mutations than affected children.
Describe the basics of the banded water snake study and explain the concepts regarding migration and gene flow that are demonstrated.
Banded vs unbanded is determined by two alleles. Banded is dominant to unbanded. On islands, the unbanded snakes have a greater reproductive advantage because they blend in better with the rocks. There are still banded snakes on the islands because every year banded snakes move from the mainland to the island and bring with them copies of the banded allele. This changes the gene pool.
Compare the new, intermediate and old bladder campion populations and describe the basic principle that is demonstrated?
There is less variation in allele frequencies among populations of intermediate age than among young and old populations. Low diversity among intermediate populations probably reflects the homogenizing influence of the gene. Migration is the movement of alleles from population to population.
What is the cause of genetic drift and is it a form of evolution?
A random process where certain alleles are selected for causing variations in allele frequency.
What three patterns does genetic drift produce?
Every population has a unique pattern of allele frequency that starts out wild and then settles down.
Drift has a larger effect on smaller populations
Can produce change in allele frequency even in large populations
What two outcomes do the wandering of allele frequencies produce?
The alleles will drift to extinction or fixation
If the allele frequency of a small population is A1 0.65 and A2 0.35, what is the probability that A2 will drift to fixation?
Explain the principles being depicted in Fig. 7.21
This figure depicts substitution when a mutation over takes the population and the new allele is substituted for the old one. It is the fixation of a new mutation
Which are more common, silent or replacement substitutions, and why?
Silent mutations are more common because they do not change the sequence therefore they are not destroyed and so they accumulate in a population much faster than replacement ones.
Differentiate between the Neutral Theory of Molecular Evolution and the Nearly Neutral model.
The Neutral theory states that the fate of new alleles is determined by drift and not natural selection for alleles that have little effect on the allele. The nearly neutral model says that rates of sequence change correlates with absolute time.
Why is the Neutral Theory so valuable
It can be used as a basis because it states that change occurs without natural selection.
Define codon bias and hitchhiking
Codon bias suggests that some synonymous mutations are not selectively mutual, codon usage is highly non-random, You'll want fast working and frequently needed mutations, then the codon can matter and be selected for. Hitchhiking, with strong positive selection acting on a particular amino acid change, as a favorable mutation increases in frequency, neutral or even slightly deleterious mutations closely linked to the favored site will increase in frequency along with the beneficial locus. The linked mutations are swept along by selection and can "hitchhike" to fixation.
What is the most common form of nonrandom mating, and how does it violate Hardy-Weinberg?
Inbreeding violates Weinberg because it does not have as large and diverse of a gene pool
How can inbreeding affect populations and what are some real-life implications?
It will reduce the heterozygote population and will cause common mutations to come together
Define Extinction Vortex
As population size decreases, there is more drift and inbreeding. The whole population will start to decline and will eventually die out
What are the potential costs of sexual reproduction?
- Sexual reproduction is very costly. The organism may spend a lot of energy searching for the mate which also takes a lot of time. This may leave you out in the open and then have a higher change of being preyed upon.
Why does asexual reproduction give a twofold reproductive edge.
- Asexual reproduction produces twice as many individuals
How common is this asexual reproduction?
- Not very common because males give help and provide variation that an asexual organism does not get which means that in the long run, asexual females really produce less offspring
- What is Muller’s Ratchet, and how does it relate to Genetic Load?
- Muller’s Ratchet indicates that in an asexual reproducing group, the group with the least amount of mutations is the most fit but by genetic drift, the most fit group is lost and so the next group with the least mutations becomes the most fit. As this continues, the population as a whole declines in fitness. The burden of accumulating mutations is called genetic load.
- Under what type of environment is sexual reproduction advantageous and why?
- Sexual reproduction is most beneficial in an environment that is missing advantageous genotypes and in an environment that is changing. Segregation and recombination in sexual selection coupled with selection is how a population evolves into a better more fit group.
. What is the connection between Parental Investment and Sexual Dimorphism?
Some genders play a larger role in raising or producing young and therefore need additional traits to successfully reproduce such as the female hollyhock weevil who need a longer snout to drill holes into the tree to lay eggs. Females use much more energy reproducing than males.
Differentiate between intrasexual and intersexual selection.
Intrasexual is when one gender fights and the other gender mates with the winner. Intersexual is when one gender chooses a mate with the best display.
. What data supports the premise that male iguana body size is not explained by natural selection?
Male iguanas that are larger get more mates is sexual selection not natural selection
What evidence did the fruit fly experiment produce that documented sperm competition?
Males whose genes were at risk of not being passed on produced larger ejaculates. They also have barbed horns on their penises that scoop out sperm from other males
Why do female lions sometimes spontaneously abort?
If a new coalition of males comes into a pride, they will kill any cubs they are not related to so the female will abort and remate so that her cubs have a better chance of surviving.
. Under what conditions does male to male competition work?
When the male cannot monopolize the females.
What are four possible explanations for female choosiness?
They may get better genes
They may have better chance of getting resources
Have a predetermined sensory bias
They may choose a mate arbitrarily
What major problem with the theory of evolution is just recently being addressed?
There is not much evidence of populations actually evolving in the wild over a long period of time.
In light of recent research, in what ways were Darwin’s predictions incorrect (this is address in both chapters 1 and 3)?
That evolution is a slow process that cannot be seen in a lifetime.
Why is Daphne Major and ideal study site?
It is an isolated area where the species cannot not easily breed and create new species. It is isolated enough that you can pinpoint the action which caused the change. Life is also harsh on this island and it faces many droughts yet the species on the island persist
Why is the Grant’s study a disaster for ornithology?
The study has such great conditions that it will be hard to create a study that will surpass the contributions that the Grant’s have made. No one will ever live up to it
Why are Darwin’s finches an ideal group of species to study?
They are from various islands with similar conditions yet all producing different species. They are also contained within the island.
What were Darwin’s first impressions of the Galapagos finches?
In the several weeks on the island, Darwin barely mentions the birds. He only says that they were comfortable around humans and just walked around hunting for seeds. He did not think they were very important.
Who originally coined the term “Natural Selection?”
Why did Darwin raise pigeons and then spend many pages discussing them in the Origin of Species?
He wanted to see natural selection firsthand. He knew that his methods of collecting the finches could come under scrutiny so he wanted to have other examples. These creatures were easily relatable and the only place that Darwin had actually seen the process work and he believed that others could see the process here too.
What are the scientific names of the small, medium and large ground finches.
Large: Geospiza magnirostris
Medium: Geospiza fortis
Small: Geospiza fuliginosa
What do blurry areas represent?
A blur refers to areas where the “tree” is growing very fast. This indicates an area where evolution is taking place rapidly.
Why did Darwin think that evolution would be slow on a small island like Daphne Major?
The population was too small.
Why did Darwin say that “nature is blind to the beak of the finch?”
Natural selection is supposed to scrutinize the slightest variation in nature but Darwin saw little change in the finch beaks over the five weeks he was there.
What does the term Hybrid Swarms mean?
Percy Lowe said this because he believed the different variation to not be different species because the variations are meaningless.
Upon reviewing his data, what did Lack discover about two species coexistence?
Species with similar beaks did not live on the same island and when they did, there was a larger difference between the two beaks than anywhere else the species existed.
What is the struggle index and what is learned from it?
The struggle index was a rating of different seeds based on their size and hardness. They were able to determine which finch was eating which seed and what struggle index the finch was eating based on the beak.
All nature is at war and the struggle very often falls on whom?
The egg and seed.
Competition is not only the clash of horns or tooth and claw, it is also what?
A silent battle where the finches just try hard to find enough seeds and when they do they just eat it.
“The smallest grain in the balance” refers to what?
The beak that can crack the largest nut is only fractions of millimeters. A small difference can mean living or dying.
Explain the relationship between Caltrop and the finches.
Where there are more finches, the Caltrop plants produce less seeds and more spines because they have a better chance at protecting their seeds.
What is the loose end that Boag wanted to tie up with his egg-switching study.
It is possible that beak size is influence by environmental factors. If a bord with a big beak can gain resources better, then it is possible that a bird with a big beak can produce more energy for a bird and its beak will grow larger despite the genes because it had a better diet.
What do we learn from the Chamaesyce plant?
Plants can affect the organisms such as this one did by depositing a sticky substance that pulled the feather off of the birds head and exposed it to the sun and death
Why was Boag so discouraged during the drought of 77?
He would measure many birds but only fractions of their offspring were able to be measured. There were so many birds that died.
What is the difference between natural selection and evolution?
Natural Selection is something that can lead to evolution but is not by itself, evolution. Natural selection takes place within a generation but evolution is across several generations.
What did Trevor Price’s analysis accomplish?
He learned which traits were actually selected for after the drought and which ones just followed along. He learned that bigger body size and a deeper beak were the traits that were selected for.
Why did selection favor both older large birds and younger small birds?
Older large birds and younger small birds are able to collect the nuts that they need. Juvenile young birds do not have fully formed jaws so they are not as strong. They need more food but have to hunt for small seeds so they are at a disadvantage
How does sexual selection differ from natural selection?
Sexual selection is less harsh than natural selection. Death vs. no mate.
. Under what circumstances is sexual selection greatest?
When there is a largely skewed sex ratio.
If females select for black plumage, why are there any brown birds?
There must also be an advantage to being brown. Brown birds are not ready to mate and so they may get into less fights with other males
. Describe the basics of Endler’s guppy experiments.
Guppy males have spots that help them camouflage in the river bed and they have seven predators. He collected the fish and counted the spots and the number of predators. He learned that the more predators, the smaller and fainter the spots. Why they all do not have the best camouflage is because to mate you need to stand out.
. Describe (don’t just name) the details of the two selection
pressures acting on the
Natural selection: The more gaudy, the higher chance of being eaten
Sexual selection: The more gaudy, the better chance of being noticed by a mate.
What is the inherent danger in courting?
You must expend a lot of energy and you might not even get chosen or get eaten
What major changes occurred in finch mating behavior during the rainy season off 1982?
Females were becoming polygamous, producing several large clutches. Young finches some even under three months were also producing clutches. Because of the rain, some birds abandoned their nests.
What caused the selection flip following the rains of 1982.
The season was very rainy so most cactus plants were not able to produce seeds. Large finches with large beaks started dying out because they had little food while there was plenty of small seeds.
Why did Smith not see any sparrow evolution on Mandarte?
He was comparing the generations at birth and at death, not year by year.
What is a Darwin?
A percentage change in the length of some characteristic. One percent in one million years=1 darwin
What do the lessons learned on Daphne Major and Mandarte teach us about the fossil record?
In real situations, we can see many Darwins of change but the fossil record shows natural selection taking place very slowly. The closer you look, the more natural selection you can see taking place but if you take a broad view it will appear slower. The fossil record is not complete enough to get a good picture.
- Why did the Grants originally believe hybrids would be at a disadvantage on the island?
- They believed that they would be less fit and be weeded out by natural selection because of it.
Which species of finches often interbred
- Fortis, fuliginosa, scandens
In what way were the hybrids the fittest finches on the island?
- They were able to produce large clutches year after year when others were dying and their clutches led to many fledglings.
- Change in variation is what?
- Why was the power of natural selection difficult to accept?
- There were not many hard facts and people still believed that it could not be seen in a lifetime.
- What did Darwin, and the Grants, do to test his theory?
- They soaked seeds in salt water to see if they would stay afloat. Then they calculated to see how many seeds of plants that were not indigenous to the island washed up on the shores.
- How do migrants fit into this picture?
- There are sometimes migrants who fly to a new island. They can stay and breed and create new populations of species on that island.
- How was Dolphs adaptive landscape useful in studying the finches?
- New species have to adapt to the landscape. Running the simulation allowed them to predict the evolution on the different islands. It identified the best fit prototype of the birds.
- How do the carpenter bees effect the finches' diet?
- Where there are bees, they compete for the flower nectar. Finches on islands with bees drink only 5% nectar while islands without bees drink 20%
- What is adaptive radiation?
- When a group forms new variations to fit into available niches.
- Explain the difference between Character Displacement and Competitive Exclusion.
- Character displacement happens most often when they are apart but competitive exclusion happens when they are together but need to move farther apart.
- What are the two barriers spoken of in this chapter?
- Sexual selection and physical barriers of the island
- Why is mate discrimination important?
- If you choose a poor mate, then your offspring will struggle to survive.
- What was the lesson learned from the cactus finches on Genovesa?
- Birds with different songs were mating with birds of different songs. The drought had divided the two species further which included mating, food choice, and type of offspring.