Question

 

 

         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.

 

 

 

Answer 1

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.