BIOLOGY 325H
NAME _______
KEY
_________________
Exam 1
Spring 2008
Page 1
1.
[15 pts.] A. Georges Cuvier showed that deeper strata of rock had creatures that differed
more from present day creatures than shallower strata.
How does this evidence support
evolution?
Since deeper strata are usually older than shallower strata (newer sediment is
deposited on older sediment), the fact that creatures in deeper/older strata are less
similar to present day creatures than creatures found in shallower/younger strata
supports the idea that organisms have evolved over time gradually changing until they
became the species we see today.
B. Explain how evolution by natural selection takes place, and do it in purely mechanistic
terms.
Do not use any language that suggests any intentionality in the process.
A population must have genetically based variation (heritable variation) for some trait.
Then because there are limited resources available in the environment, e.g., food,
nesting sites, water, nutrients, etc., and because organisms nearly always produce
more offspring than the environment can support, the offspring that have the best
phenotype for the environment in which they live are more likely to survive to adulthood
and may also produce more offspring.
Thus in the next generation, the genes that
produced the favored traits in the previous generation will increase in frequency in the
population due to those individuals having more offspring relative to the individuals with
the phenotypes that survived and reproduced at a lower rate.
C. Why is it necessary to distinguish sexual selection from natural selection?
Sexual selection differs from natural selection because it affects the traits of one sex
more than the other, e.g., secondary sexual characteristics such as color in many
species of male birds.
In addition, sexual selection and natural selection can
sometimes act in opposite directions, such as the example of the tail feathers in the
widow birds.
Sexual selection favored longer feathers, whereas natural selection
favored shorter feathers.
2
. [15 pts.] Yucca is a succulent plant native to Texas, and entomologist Carmen Elytra
studies a beetle species that lives on this plant. Yucca beetles with a homozygous recessive
yy
genotype are green in color, while the genotypes
YY
and
Yy
result in a blue color. Carmen
observes that the green beetles are 5 times more likely to be eaten by birds when located
on blue yucca, and that blue beetles are 5 times more likely to be eaten by birds when
located on green yucca.
Carmen releases equal numbers of green and blue beetles in two experimental gardens: one
garden contains only green yucca; the other garden contains only blue yucca.
A. Assume natural selection is the only factor
that affects allele frequency in these two
populations. Describe the expected change(s) in the frequency of the
Y
and
y
alleles over
subsequent generations in each of the two gardens.
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- Spring '08
- Staff
- Genetics, Evolution, BIOLOGY 325H Exam, yucca garden
-
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