Download Module 5 Homework Assignment

Module 5 Homework Assignment
BIO130: Fundamentals of Biology
Bobbi Randall
Karen Everett
26 March 2010
2010-06-1727250-BIO130-M5HW-BRandall.doc
Homework Assignment 5
BIO 130: Fundamentals of Biology
1. Describe the biological meaning of the word evolution.
Evolution is a change in the frequency of genetically determined characteristics within a
population over time. This change could be what is considered a minor change in allele
frequency or a microevolution. The change could also be on a larger scale where larger changes
are made over a period of time to create a new species, or macroevolution.
2. Why has Lamarck’s theory been rejected?
Lamarck’s theory was rejected because it was based on acquired characteristics or traits
obtained over an organism’s life and are not genetically determined. Acquired characteristics are
not transmitted to offspring making them impossible to pass on.
3. List five assumptions about the nature of living things that support the concept of
evolution by natural selection.
1. All organisms produce more offspring than can survive, 2. No two organisms are exactly
alike, 3. Among organisms, there is a constant struggle for survival, 4. Individuals that possess
favorable characteristics for their environment have a higher rate of survival and produce more
offspring, 5. Favorable characteristics become more common in the species, and unfavorable
characteristics are lost.
4. List three factors that can lead to changed gene frequencies from one generation to the
next.
1. Population is a factor that can lead to changed gene frequencies from one generation to the
next, 2. Mutation is another factor that can lead to changed gene frequency from one generation
to the next, 3. Migration is another factor that can lead to changed gene frequencies from one
generation to the next.
5. Why is each of the following important for an understanding of evolution: mutation,
migration, sexual reproduction, selective agents, and population size?
Mutation is important for understanding of evolution because mutations bring about allele
change which introduces new gene frequencies. Migration is important for an understanding of
evolution because migrating species can come in contact and mate with other varieties of their
species and introduce new alleles through sexual reproduction. Sexual reproduction is important
to understand for evolution because species are able to select partners with different allele
frequencies which introduce different gene frequencies. Selective agents are important to
understand evolution because they are used to select which parts of the species is going to live or
die or basically have the traits that will provide for success of the species. Population size is
important for understanding evolution because the larger the population, the more diverse the
gene pool will be. With smaller population sizes, you only have the genes available to reproduce
and keep the species alive.
6. How is the concept of gene flow related to the species concept?
The species concept is an attempt to define groups of organisms that are reproductively isolated
and, therefore, constitute a distinct unit of evolution. Some species are completely isolated from
other, closely related species and do fit the definition well; some have occasional exchanges of
genetic material between species and do not fit the definition as well; and some groups
interbreed so much that they must be considered distinct populations of the same species (Enger,
Homework Assignment 5
BIO 130: Fundamentals of Biology
2008). The above passage describes the species concept while the following passage describes
the gene flow concept. One way to find out if two populations belong to the same species is to
think about gene flow, the movement of genes from one generation to the next as a result of
reproduction or from one region to another by migration. Two or more populations that
demonstrate gene flow among them constitute a single species. On the other hand, two or more
populations that do not have gene flow through reproduction, when given the opportunity, are
generally considered to be different species (Enger, 2008). My understanding of this question is
this, both concepts deal with population distance and lack of migration. The best example of
these concepts are the description of the horse, donkey and resulting mule and how horses and
donkeys do not breed together in the wild but can be bred in captivity.
7. How does speciation differ from the formation of subspecies?
Speciation is the process of generating new species. When evolutionary biologists look at the
evolutionary history of living things, they see that new species have arisen continuously for as
long as life has been on Earth (Enger, 2008). Within a population, genetic material is repackaged
into new individuals from one generation to the next. Often, there is very little adding or
subtracting of genetic material from a local population of organisms, and a widely distributed
species consists of a number of more or less separate groups, known as subspecies(or breeds,
varieties, strains, or races). All of these terms are used to describe various forms of organisms
that are all members of the same species (Enger, 2008). Based on these two definitions,
speciation differs from the formation of subspecies by speciation being the creation of a whole
new species whereas subspecies is just an adapted genetically similar subspecies.
8. Describe three kinds of reproductive isolating mechanisms that prevent interbreeding
between different species.
Habitat preferences, or ecological isolating mechanisms, occur when two species do not have the
opportunity to interbreed because they typically live in different ecological settings. For
example, in central Mexico, two species of robin-sized birds, called towhees, live in the same
general region. However, the collared towhee lives on the mountainsides in the pine forest,
whereas the spotted towhee is found at lower elevations in oak forests. Geography presents no
barriers to these birds. They are capable of flying to each other’s habitats, but they do not.
Therefore, they are reproductively isolated because of the habitats they prefer. Similarly, areas
with wet soil have different species of plants than nearby areas with drier soils (Enger, 2008).
Seasonal isolating mechanisms(differences in the time of year at which reproduction takes place)
are effective genetic isolating mechanisms. Some plants flower only in the spring, whereas other
species that are closely related flower in midsummer or fall; therefore, the two species are not
very likely to pollinate one another. Among insects, there are examples of similar spacing of the
reproductive periods of closely related species, so that they do not overlap (Enger, 2008).
Hybrid inviability, or infertility mechanisms, prevent the offspring of two different species from
continuing to reproduce. This can occur in three ways: (a)the embryos of such a mating may not
develop properly and die; (b)if offspring are produced, they die before they can reproduce; or (c)
such hybrids may be sterile or have greatly reduced fertility (Enger, 2008).
Homework Assignment 5
BIO 130: Fundamentals of Biology
9. Give an example of seasonal isolating mechanisms, habitat preference, and behavioral
isolating mechanisms.
Seasonal Isolating Mechanisms: Some plants flower only in the spring, whereas other species
that are closely related flower in midsummer or fall; therefore, the two species are not very likely
to pollinate one another (Enger, 2008).
Habitat Preference: in central Mexico, two species of robin-sized birds, called towhees, live in
the same general region. However, the collared towhee lives on the mountainsides in the pine
forest, whereas the spotted towhee is found at lower elevations in oak forests (Enger, 2008).
Behavioral Isolating Mechanisms: groups of male prairie chickens gather on meadows shortly
before dawn in the early summer and begin their dances. The air sacs on both sides of the neck
are inflated, so that the brightly colored skin is exposed. Their feet move up and down very
rapidly and their wings are spread out and quiver slightly. This combination of sight and sound is
attractive to females. When the females arrive, the males compete for the opportunity to mate
with them (Enger, 2008).
10. Why is it difficult to determine the evolutionary history of a species?
It is difficult to determine the evolutionary history of a species because of divergent evolution
factors, extinction, adaptive radiation, and convergent evolution. All of these factors play a role
in a species evolutionary background making it difficult to determine the evolutionary history
(Enger, 2008).