I need them answered ASAP, thank you in advance!!!!!! Problem Set 8 Addendum : 1

Question

I need them answered ASAP, thank you in advance!!!!!!

         Problem Set 8 Addendum:

1.      There is one more topic in population genetics that I wanted to touch on, but did not get a chance to cover in lecture. We did discuss why genetic drift is of concern in zoo populations due to small population size. Related phenomena are when a natural population goes through a population bottleneck (a reduction of population size due to a severe natural event (flood, fire, severe storm) or due to human activity (habitat destruction, hunting to near extinction) or a founder effect (i.e. a small founder population derived from a larger mainland population is established on an island). See Campbell p. 493. In such events the chance survivors or chance founders (not based on better traits, just chance) represent very small numbers of individuals and in such cases the effects of drift can be very strong.

            Elephant seals are a good example of the effect of a population bottleneck on the level of genetic variation in the population. In the 1890s hunting reduced the northern elephant seal population from thousands of individuals to 20 individuals. Under a hunting ban the population increased and now numbers about 30,000. In a sample of 24 protein coding genes in the present-day population , only three loci were polymorphic. The level of polymorphism was much higher in the southern elephant seal population, that was not reduced to very low population size. In the northern population, the population size has increased, but the level of genetic variation has not. The northern and southern elephant seals are different species and separated geographically, so migration between the northern and southern populations cannot replenish genetic variation in the northern elephant seals. What is the only force that can replenish genetic variation in the Northern elephant seal population? Why hasn’t this force been able to replenish genetic variation in >100 years? Answer: the only force of evolution that can replenish genetic variation in the population is mutation. Mutations rates are so low that it will take thousands of generations for mutation to replenish genetic variation in the northern elephant seal population. A similar example is discussed in Campbell (pp.493-494).

            Problem Set 9           

            Use your lecture notes, lecture slides, and Campbell text to answer the questions below.

1.      Use class notes and Campbell’s section on Hierarchical Classification (pp. 552-553) to answer the following. Explain the Linnaean system of classification used to organize biological diversity. This system of classification is a hierarchical system. What does that mean? Define a Genus. What is a Family, and why would members of several genera be placed in the same family? You could answer the same for higher level groups up the taxonomic hierarchy. How do biosystematists (biologists who classify organisms, also sometimes called “taxonomists”) decide where to place a newly described species within the hierarchy? Answer: a systematist who is an expert in a particular group (a Family of beetles for example) analyzes the phenotypic and genetic similarity of the new species to existing known species in the Family to decide in which Genus to place the new species).

   2.      Explain how species are defined under the Biological Species Concept (BSC) (see class notes and Campbell pp. 505-508).   Reproductive isolation is an important part of the BSC. What is meant by reproductive isolation of two species? Note that the test of the BCS is that two species must be reproductively isolated in Nature. Horses and donkeys can mate and produce a hybrid mule offspring that is sterile. Why are horses and donkeys considered different species under the BSC? How do the different diploid numbers in the two species help explain hybrid sterility? (Note that to produce a mule horses and donkeys are forced to mate by humans and this only occurs under domestication, not in nature).

3.       Explain in general terms geological theory of uniformitarianism originally proposed by Hutton and later supported by Lyell.   Why did this theory suggest that the age of the earth was many millions of years? Lyell was a contemporary and friend of Darwin.

            S18: We did not discuss the theory of uniformitarianism this year, but geologists before and during Darwin’s time had proposed that the earth was far older than the 6,000 year age accepted by biblical creationists of the time (and accepted by most of the scientific “establishment”). Briefly, the geological theory of Uniformitarianism proposed that the monumental geological formations that we observe on earth today (the Grand Canyon for example) were produced over extremely long periods of time by the same slow gradual geological processes (erosion, deposition of sediments, volcanism) that we see operating around us today. Based on his observations and calculations Lyell (a geologist and friend of Darwin) estimated that the earth was more that 300 million years old. Today geologists using modern methods estimate the age of the earth at approximately 4.6 billion years. Darwin was strongly influenced by Lyell’s writings on uniformitarianism and used the idea of slow gradual change over long periods of geologic time in his explanation of how complex adaptations form from originally simple forms. The idea of uniformitarianism was also important because it provided the time scale necessary for process of evolution to produce the diversity of life that we observe around us and in the fossil record.

   4.      Why do you think Darwin became so interested in plant and animal breeding and did artificial selection experiments with pigeons (see class notes and Campbell fig. 22.9)?   Outline the Components of Darwin's Theory of Evolution by Natural Selection, and how the components interact to bring about evolutionary change (Use the components outlined in the Lecture Slides shown in class, but it is also useful to read Campbell on Artificial Selection, Natural Selection, and Adaptation pp. 472-474). Be sure to explain the meaning of Reproductive Excess and how it would produce a Struggle for Existence. What is the Reproductive Fitness of a phenotype and underlying genotype (same definition we used in population genetics)? In artificial selection the plant or animal breeder decides which phenotypes in the population are permitted to breed (i.e. have higher fitness than those phenotypes that the breeder does not permit to breed). What determines why certain phenotypes have higher fitness than other phenotypes in Natural Selection? Explain why there must be genetic variation for a trait in a population for natural selection to increase the frequency of favorable phenotypes in the population over time (refer back to our discussion of this idea in quantitative genetics).

   5.      Explain how the Components of Natural Selection you outlined above can be applied to the Grant’s work on the evolution of beak size in their study population of the medium ground finch on the Galapagos. What was the evidence that genetic variance affecting phenotypic variance of beak size existed in the population? What change in the environment altered the fitnesses of different phenotypes during the drought? Why would the conditions during the drought have intensified the struggle for existence among individuals with different phenotypes? What is the evidence that individuals with larger beak had a fitness advantage over individuals with smaller beak? (see Lecture slides)

   6.      Natural Selection operates at the level of the phenotype. Use the finch example above to illustrate how selection operating on phenotypes can result in a change of the genetic composition of a population over time. Assume that phenotypic variation in beak size has an underlying additive genetic basis (recall your answer to question 5 in the Quantitative Genetics Exercise).

   7.      When is a specific phenotype for a trait in a population considered an adaptation? Why would larger beak size be considered an adaptation in the finch population. What was Darwin’s general explanation for how complex adaptations evolve? Use the example of the evolution of the complex eye of the squid to illustrate. How did Darwin use the eyes of different living mollusk species to support his hypothesis (see lecture slides, Campbell pp.545-546, and Fig. 25.28? See Fig. 25.7 in Campbell that illustrates the gradual changes in skull, jaw and tooth morphology over a period of 120 million years (!) in the evolution of mammals from synapsids documented in the fossil record.

   8.      Read the section in Campbell Key Features of Natural Selection on p. 474. and class notes to explain why “individuals do not evolve, populations evolve over time”.

   8.      What is the role of random mutation in the Two-Step Process of Adaptive Evolution? What is the role of the non-random force of Natural Selection?

   9.      Give one possible reason why Natural Selection can’t be expected to produce the best imaginable adaptation (optimal phenotype) in a population? Use the example of sickle-cell trait as an adaptation to malaria to illustrate. Another reason why Natural Selection can’t be expected to produce the optimal phenotype in a population is that the environment is constantly changing (so the theoretically optimal phenotype is also constantly changing).

Explanation / Answer

Ans 1) The Linnaean system of classification was something that was defined by Carolus Linnaeus who also defined humans in 1758. It is the system of classifying and naming the organisms based on their hierarchy. He proposed that there are three broad categories called as kingdoms based on hierarchy which are animals, plants and minerals. This was the oldest and most primitive form of classification. The genus is a rank in the biological classification which is above species and below the family. The genus contains one or more species. Family is one of the major taxonomic ranks and families can be divided into sub-families which are intermediate ranks that is above the genus. The members of the several genera can be placed in same family and the members can be placed in the same family due to their close resemblance and similarity. Systematist is a scientist who is involved in study of the living organisms and helps in the study of the diversification of the living forms that include both past and present. They help in visualizing the living things and connect the path of evolution through evolutionary tree.

Ans 2) Species are a group of the living organisms that form a part of the taxonomic classification and it is below the genus. It is infact the lowest in the nomenclature. Reproductive Isolation is collection of evolutionary mechanism along with the behavior and physiological process that prevents members of different species to produce offspring together. Even if they produce the offspring, it is sterile. The horses and donkeys are considered different species under BSC as the mating between the two produces mule which is sterile and hence cannot be of same species. There is reproductive isolation observed and seen in both.

Ans 3) The theory of uniformitarianism in ecology states that the geological processes on the Earth acted in same manner and intensity in the past as they do during the present time. However, due this and such uniformity, the geological changes occurred. This stated that there have been uniform processes of change and that led to all the geological differences. The theory suggest that age of Earth is millions of years old as the changes have taken in very uniform way which takes a lot of time.

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