Download 2-16-16 Types of Selection Work

1.
Types of Natural Selection
Natural Selection is the basis of evolution. Describe the steps that lead to natural selection in an
environment.
a.
b.
c.
d.
e.
2.
One of the steps that leads to natural selection (and one that should’ve been listed in your response to #1) is
that there is genetic variation. There are 2 major factors that lead to this genetic variation that are listed
below. Explain how each ALWAYS results in genetic variation.
a. Mutations (Explain how this is the only factor that creates completely new, unique genotypes)
b.
Sexual reproduction (Explain how each of the following aspects of sexual reproduction lead to
variation (although they do not create new alleles).
i. Crossing over
ii. Segregation of homologous chromosomes
iii. Independent assortment of homologous chromosomes
iv. Random fertilization
3.
In question #2 you explained how genetic variation is created. Now, explain the 5 processes that causes
evolution to happen. (Note to remember when answering this question: Evolution is simply a change in
allele frequency in a gene pool. Or in other words, evolution is simply 1 genetic variation being favored
over another). Hint: The 5 things that can cause evolution to happen will be the OPPOSITE of the 5
rules for Hardy-Weinberg Equilibrium. This should make sense because Hardy-Weinberg
Equilibrium is when a population’s gene pool is not changing while evolution is when a gene pool is
changing.
a.
b.
c.
d.
4.



e.
Natural selection can affect a population in many ways. For each of the following types of natural selection,
tell what range of phenotype is selected AGAINST?
Directional
Disruptive
Stabilizing
5.

For each of the following types of natural selection, tell what range of phenotypes are seen in a population
AFTER the selection has occurred? (Hint: For each of these types of selection, you will choose one of the
following to indicate what the population’s phenotype looks like AFTER evolution: 1) The majority of the
population shows the “normal” phenotype, 2) The majority of the population shows only one of the
extreme ends of the phenotypic range, or 3) The majority of the population demonstrates both ends of the
phenotypic range but very few show the “normal” phenotype)
Directional

Disruptive

Stabilizing
6.
Draw a diagram showing the original population, the new population, and the section of the phenotypic
range that was being chosen against for each of the following types of selection.
Directional
a)
b) Disruptive
c)
Stabilizing
For the situations described in questions 7-15 tell whether each of them are directional, disruptive, or
stabilizing selection.
7.
People that have lived in higher altitudes (i.e. Colorado) have a greater lung capacity than the average U.S.
citizen. __________________________________________
8. The teeth of modern humans are smaller than ancestral humans because our diet has become less coarse
(not as tough) over the last few million years. ________________________________
9. Charles Darwin observed many different species of Finches on the Galapagos Islands. On each of these
different islands, Darwin noticed that the Finch species had very different beaks. There were no “average”
sized beaks; rather, they were each specialized for the food on their particular island.
_____________________________________________
10. There is a very high incidence of infant mortality for very heavy as well as very light babies. ____
____________________________
11. Coho salmon are either very large or very small due to the fact that these respective sizes both pose
reproductive benefits. There are very few “normal” sized coho salmon. ______________
_______________________________
12. In ancient humans, very small men might not be very attractive to women because they can't defend their
family as well but large men might have a more difficult time finding enough food. Very large men would
tend to be slower and have less endurance. ________________________
13. Giraffes fight for their mates by swinging their long necks and hitting each other with their heads. This has
caused their neck to become longer over time because giraffes with longer necks can swing their necks
faster (and thus win the fights for the mate). ________________________
14. Remember the incidence of peppered moths. White moths had previously been more reproductively
successful due to the fact that they blend in with the lichen on the trees. With the recent rise in pollution,
the black moths now have more reproductive success because they blend in with trees blackened from
pollution. _________________________________________
15. Dog breeding could be considered disruptive selection because breeders intentionally breed dogs that show
extreme phenotypes. Even so, the fact that this form of selection is not natural (it is caused by humans
forcing it to happen) means that it is actually what kind of selection?
________________________________________________