Chapter 16 & 17
Review Questions
List 5 Pre-Zygotic Barriers (Isolation Mechanisms) and give an example for each
Temporal – When two populations become separated by time. This may be cause by
breeding at different times. Ex. Similar orchids that live in jungle release pollen
only on a single day and the days are different so they can’t pollinate one another
Geographic – When two populations become separated by physical change on the
earth. This separation may be caused by a change in geologic features such as the
formation of mountains, canyons, rivers, or glaciers. Ex. Albert and Kaibab Squirrels
that live on opposite sides of the Grand Canyon.
Behavioral – When two populations are separated due to their different behaviors, such
as mating song or dance, or attraction to different colors. Ex. Eastern and Western
Meadowlarks use different songs to attract a mate.
FROM ACTIVITY:
Mechanical – When two populations have different structures necessary for mating.
Ex. Male damselflies can’t grasp and hold the females of another species.
Gametic Isolation – The gametes of two populations cannot interact. Ex. The sperm
of sea urchins are unable to attach to the eggs of another species
List 2 Post –Zygotic Barriers (Isolation Mechanisms) and give an example for each
Hybrid Sterility – When two populations can interbreed to produce offspring, but the
offspring are sterile and cannot reproduce. Ex. Horses and donkeys mate to
produce the sterile mule.
Hybrid Inviability – When two populations can interbreed to produce offspring, but
these offspring do not live for very long, or do not develop to reproductive age. Ex.
Different species of frogs mate but the zygotes don’t survive to hatch.
What is a Polygenic Trait? Give an example and how is it graphed?
A polygenic trait is a trait that has two or more genes that produce it. They may be
found on different chromosomes. Many phenotypes are produced. An example is skin
color and the graph resembles a bell curve.
How is a single gene trait graphed? Give an example.
A single gene trait is graphed using a bar graph. An example of a single gene trait is
blood type. Single gene traits tend to have 1-4 phenotypes.
Define Directional, Disruptive, and Stabilizing Selection. What does the graph look like
for each.
Directional Selection is where one end of the bell curve exhibits greater fitness so the
graph shifts toward that end.
Stabilizing Selection is where the individuals in the middle range have greater fitness
than the individuals at the ends. The bell curve narrows by reducing both ends of the
curve.
Disruptive Selection is where the two ends show greater fitness than the individuals in
the middle (intermediate type). The result is the bell curve dipping in the middle.
What is Genetic Drift? Define Genetic Bottleneck & founder effect. Include examples in
your definition.
Genetic Drift is the random change in allele frequency. This can be caused by a
genetic bottleneck where the population is reduced and a few individuals survive.
These individuals do not contain all the alleles that were found in the original population.
This has happened to the cheetah where man has decimated the population. The
founder effect is where a small number of individuals are isolated and reproduce. This
may eliminate some alleles and other alleles like the polydactyl gene in the Amish
population become more frequent.
What are the five Agents of Change?
Mutation is an alteration in DNA and is the ultimate source of variation.
Gene Flow is the movement of alleles from one population to another. This occurs
when individuals move between populations.
Genetic Drift is the random alteration of allele frequency in a population. This readily
occurs during a bottleneck or founder effect.
Non-Random Mating occurs when one member of a population is not equally likely to
mate with any other member of the population.
Natural Selection is where some members will be more successful in mating and
reproduction.
What are the five conditions necessary for Genetic Equilibrium (Hardy-Weinberg)?
a. The population is very large.
b. The population is isolated (no migration of individuals, or alleles, into or out of the
population).
c. Mutations do not alter the gene pool.
d. Mating is random.
e. All individuals are equal in reproductive success (no natural selection).
What types of elements are used to determine the age of mineral deposits (rocks)?
Elements with radioactive isotopes are used to determine the age of mineral deposits.
These include elements like Potassium-40 (non-living) or Carbon-14 (once living
things).
Define half-life.
Half-life is the length of time required for half the radioactive atoms in a sample to
decay.
Describe how a fossil is formed.
A fossil may be formed when an organism dies and then is immediately covered with
sediment. If conditions are right the remains remain intact and free from decay
organisms. Over time more sediment is built up over the organism. While this is
occurring other minerals are turning it into rock.
Describe how the modern atmosphere formed.
The modern atmosphere began to be formed when cyanobacteria became capable of
photosynthesis. They released oxygen into the oceans where it first bonded to most of
the iron dissolved in the water. It then saturated the water and began to be released
into the atmosphere. Over time enough oxygen made it into the upper atmosphere
where it is able to form ozone to filter out most of the harmful UV radiation.
What is an Era and how is it divided. Give an example.
Geologists have created 4 eras to generally describe events that happen during that
time period. They are divided into periods that give a little more detail to events
occurring during that specific period of time. For example the Mesozoic Era has 3
periods: Triassic, Jurassic, and Cretaceous.
Cenozoic Era – Age of Mammals
Mesozoic – Age of Dinosaurs
Paleozoic – Age of Fishes
PreCambrian – First signs of life
Explain mass extinction and give two examples. When did they occur?
Mass extinctions occur when over 75% of living organisms go extinct in a geologically
short period of time (A few thousand to a few hundred thousand years). A mass
extinction occurred about 245 million years ago. This was the end of the Permian
period of the Paleozoic Era and ended the Paleozoic Era and ushered in the Mesozoic
Era. Another occurred about 65 million years ago with a meteor impact on the Yucatan
Peninsula that ended the Mesozoic Era and started the Cenozoic Era.
Compare and contrast relative dating and radioactive dating.
Relative dating can determine the age of a fossil with respect to another rock or fossil
(that is, older or younger) and is performed by comparing the depth of a fossil’s source
stratum to the position of a reference fossil or rock. The age is imprecise
Radioactive dating can determine the age of a fossil in years and is performed by
determining the relative amounts of a radioactive isotope and nonradioactive isotope in
a specimen. It is difficult and expensive to perform.
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b